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Nanodiamond-Rich Layer Across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP

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A major cosmic-impact event has been proposed at the onset of the Younger Dryas (YD) cooling episode at ≈12,800 ± 150 years before present, forming the YD Boundary (YDB) layer, distributed over >50 million km2 on four continents. In 24 dated stratigraphic sections in 10 countries of the Northern Hemisphere, the YDB layer contains a clearly defined abundance peak in nanodiamonds (NDs), a major cosmic-impact proxy. Observed ND polytypes include cubic diamonds, lonsdaleite-like crystals, and diamond-like carbon nanoparticles, called n-diamond and i-carbon. The ND abundances in bulk YDB sediments ranged up to ≈500 ppb (mean: 200 ppb) and that in carbon spherules up to ≈3700 ppb (mean: ≈750 ppb); 138 of 205 sediment samples (67%) contained no detectable NDs. Isotopic evidence indicates that YDB NDs were produced from terrestrial carbon, as with other impact diamonds, and were not derived from the impactor itself. The YDB layer is also marked by abundance peaks in other impact-related proxies, including cosmic-impact spherules, carbon spherules (some containing NDs), iridium, osmium, platinum, charcoal, aciniform carbon (soot), and high-temperature melt-glass. This contribution reviews the debate about the presence, abundance, and origin of the concentration peak in YDB NDs. We describe an updated protocol for the extraction and concentration of NDs from sediment, carbon spherules, and ice, and we describe the basis for identification and classification of YDB ND polytypes, using nine analytical approaches. The large body of evidence now obtained about YDB NDs is strongly consistent with an origin by cosmic impact at ≈12,800 cal BP and is inconsistent with formation of YDB NDs by natural terrestrial processes, including wildfires, anthropogenesis, and/or influx of cosmic dust.
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[The Journal of Geology, 2014, volume 122, p. 475–506] !2014 by The University of Chicago.
All rights reserved. 0022-1376/2014/12205-0001$15.00. DOI: 10.1086/677046
475
ARTICLES
Nanodiamond-Rich Layer across Three Continents Consistent with
Major Cosmic Impact at 12,800 Cal BP
Charles R. Kinzie,
1,
*Shane S. Que Hee,
2
Adrienne Stich,
1
Kevin A. Tague,
1
Chris Mercer,
3
Joshua J. Razink,
4
Douglas J. Kennett,
5
Paul S. DeCarli,
6,
Ted E. B unch,
7
James H. Wittke,
7
Isabel Israde-Alca´ntara,
8
James L. Bischoff,
9
Albert C. Goodyear,
10
Kenneth B. Tankersley,
11
David R. Kimbel,
12
Brendan J. Culleton,
5
Jon M. Erlandson,
13
Thomas W. Stafford,
14
Johan B. Kloosterman,
15
Andrew M. T. Moore,
16
Richard B. Firestone,
17
J. E. Aura Tortosa,
18
J. F. Jorda´Pardo,
19
Allen West,
20,
James P. Kennett,
21
and Wendy S. Wolbach
1
ABSTRACT
A major cosmic-impact event has been proposed at the onset of the Younger Dryas (YD) cooling episode at 12,800 "
150 years before present, forming the YD Boundary (YDB) layer, distributed over 150 million km
2
on four continents.
In 24 dated stratigraphic sections in 10 countries of the Northern Hemisphere, the YDB layer contains a clearly
defined abundance peak in nanodiamonds (NDs), a major cosmic-impact proxy. Observed ND polytypes include cubic
diamonds, lonsdaleite-like crystals, and diamond-like carbon nanoparticles, called n-diamond and i-carbon. The ND
abundances in bulk YDB sediments ranged up to 500 ppb (mean: 200 ppb) and that in carbon spherules up to 3700
ppb (mean: 750 ppb); 138 of 205 sediment samples (67%) contained no detectable NDs. Isotopic evidence indicates
that YDB NDs were produced from terrestrial carbon, as with other impact diamonds, and were not derived from
the impactor itself. The YDB layer is also marked by abundance peaks in other impact-related proxies, including
cosmic-impact spherules, carbon spherules (some containing NDs), iridium, osmium, platinum, charcoal, aciniform
carbon (soot), and high-temperature melt-glass. This contribution reviews the debate about the presence, abundance,
and origin of the concentration peak in YDB NDs. We describe an updated protocol for the extractionand concentration
of NDs from sediment, carbon spherules, and ice, and we describe the basis for identification and classification of
YDB ND polytypes, using nine analytical approaches. The large body of evidence now obtained about YDB NDs is
strongly consistent with an origin by cosmic impact at 12,800 cal BP and is inconsistent with formation of YDB
NDs by natural terrestrial processes, including wildfires, anthropogenesis, and/or influx of cosmic dust.
Online enhancements: appendixes.
Introduction
The Younger Dryas (YD) impact hypothesis pro-
poses that a major cosmic-impact event occurred
at the Younger Dryas Boundary (YDB) 10,900 "145
radiocarbon years before present (RCYBP), a time
corresponding to the onset of the YD cooling re-
corded in Greenland Ice Sheet cores and other se-
Manuscript received May 19, 2013; accepted April 18, 2014;
electronically published August 26, 2014.
* The authors’ affiliations can be found at the end of the
article.
Deceased.
Author for correspondence;e-mail:allen7633@aol.com.
quences (Firestone et al. 2007). The published
IntCal radiocarbon curve has recently been revised
(Reimer et al. 2013) and provides a calibrated age
for this radiocarbon date of 12,830 "130 cal BP
at 1 standard deviation (j). This differs from earlier
calibrated ages for the YDB of 12,900 "100 cal BP,
used by Firestone et al. (2007), and 12,800 "150
cal BP, more recently used by Wittke et al. (2013).
Because this latest adjustment represents a differ-
ence of only 30 yr, we continue to use an age of
12,800 "150 cal BP for the YDB. We emphasize
that, although the calendar calibration has
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476 C . R . K I N Z I E E T A L .
changed, the radiocarbon age has remained the
same.
The proposed impact deposited the YDB layer,
which contains many cosmic-impact proxies, in-
cluding magnetic and glassy impact spherules, irid-
ium, fullerenes, carbon spherules, glass-like car-
bon, charcoal, and aciniform carbon, a form of soot
(Firestone et al. 2007; Wittke et al. 2013). In North
America and the Middle East, Bunch et al. (2012)
identified YDB melt-glass that formed at high tem-
peratures (1730#to 12200#C), as also reported by
three independent groups, Mahaney et al. (2010) in
South America and Fayek et al. (2012) and Wu et
al. (2013) in North America. This study focuses
solely on nanodiamonds (NDs), and so, for inde-
pendent discussions of other proxies, see Haynes et
al. (2010) and Paquay et al. (2009), who found no
evidence for the platinum-group elements iridium
or osmium. Alternately, Wu et al. (2013) found large
YDB anomalies in osmium, as discussed below.
Also, in a Greenland ice core, Petaev et al. (2013)
found a large YDB abundance peak in the platinum-
group element platinum. Surovell et al. (2009)
found no YDB peaks in magnetic spherules,
whereas LeCompte et al. (2012) found large, well-
defined YDB spherule peaks at sites common to
the study by Surovell et al. Also, critical overviews
of the YDB hypothesis are presented in Pinter et
al. (2011) and Boslough et al. (2012).
Recently, the YDB cosmic impact was indepen-
dently confirmed by Petaev et al. (2013), who re-
ported compelling evidence from a well-dated
Greenland Ice Core Project (GISP2) ice core exhib-
iting a sharp abundance peak in platinum precisely
at the YD onset (12,877 "3.4 cal BP). Those au-
thors’ mass-balance calculations indicate that the
platinum peak resulted from a major cosmic-
impact event by an impactor estimated to be at
least 1 km in diameter. Similarly, Wittke et al.
(2013) estimated that the tonnage of YDB ejecta
(spherules and melt-glass) is comparable to that
ejected from the 10.5-km-wide Bosumtwi Crater,
likely produced by a 1-km-wide impactor. The
GISP2 platinum peak is coeval with the abrupt on-
set (1.5 yr) of the atmospheric changes that mark
the YD climatic episode in the North Greenland
Ice Core Project (NGRIP) ice core at 12,896 cal BP
(Steffensen et al. 2008). The discovery of such an
unequivocal impact proxy at the YD onset in the
Greenland record was predicted by the YDB impact
hypothesis when it was initially introduced (Fire-
stone et al. 2007).
The comprehensive impact proxy assemblage in
the YDB layer also includes NDs and diamond-like
carbon, which were discovered within carbon
spherules, glass-like carbon, and bulk sediment.
The polymorphs of carbon extracted from bulk sed-
iment and carbon spherules include cubic NDs and
hexagonal lonsdaleite-like crystals as well as
unique carbon allotropes, called n-diamonds and i-
carbon (details in table D1; apps. A–D available on-
line). These latter two types of nanocrystals, almost
as hard as cubic NDs, are frequently used in thin,
polycrystalline films for industrial applications re-
quiring hardness and abrasion resistance (Wen et
al. 2007). Ongoing investigations have been ex-
amining whether these polymorphs are simply cu-
bic diamonds with atomic substitution of carbon
by hydrogen or other elements (Wen et al. 2011) or
are new forms of diamond-like carbon (Hu et al.
2012). Regardless, the nanoparticles in question
form under exotic temperatures and pressures not
present naturally at the Earth’s surface or lower
atmosphere but similar to conditions related to cos-
mic impact (Wen et al. 2007) and are unlike other
forms of carbon typically found naturally on Earth.
For simplicity, we refer to all forms as NDs, even
though n-diamonds and i-carbon may actually be
only diamond-like. YDB NDs were most likely
formed from terrestrial carbon, based on their car-
bon isotopic composition (Tian et al. 2011; Israde-
Alca´ntara et al. 2012b), and are similar to NDs
formed during the cosmic impact at the Creta-
ceous-Paleogene boundary (K-Pg, formerly referred
to as the K-T; Gilmour et al. 1992).
The YDB carbon spherules that contain NDs are
morphologically and compositionally similar to
younger carbon spherules first reported in near-sur-
face forest soils of Europe by Ro¨sler et al. (2005),
who first suggested an impact-related origin of the
particles. Later, some of the same authors (Yang et
al. 2008) stated, “Whether this would have occurred
during or before any impact is still unclear fornow”
(p. 943). Carbon spherules have been proven to form
in cosmic-impact events, as shown by the discovery
of a !1100-yr-old meteorite crater in Alberta, Can-
ada (Newman and Herd 2013). Some carbon spher-
ules are fused to fragments of the meteorite, indi-
cating that they formed upon impact. Their
morphology includes an exterior shell around a
highly vesicular interior, identical to YDB spher-
ules and carbon spherules found in Europe. Carbon
spherules have also been reported from experi-
ments using hypervelocity impacts into carbon-
rich substrates, duplicating cosmic-impact condi-
tions (Heymann et al. 2006). Furthermore, carbon
spherules containing NDs have been demonstrated
to form from tree sap under laboratory conditions
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 477
that duplicate the temperature, pressure, and redox
values within an impact fireball (Israde-Alca´ntara
et al. 2012b).
Following the identification of NDs by Kennett
et al. (2009a, 2009b), Daulton et al. (2010) at-
tempted to replicate that discovery at two well-
known archaeological sites, Murray Springs, Ari-
zona, and Arlington Canyon, California. Daulton
et al. (2010) found no YDB NDs and concluded that
their findings cast doubt on the presence of YDB
NDs, although they pointed out that YDB NDs
might “occur inhomogeneously and only in some
of the YD-boundary carbons and hence are not ob-
served in our study” (p. 16046). Daulton et al. (2010)
also noted that other minerals, including nano-
crystalline copper and copper oxide, could be mis-
identified as several of the proposed diamond poly-
types, because of crystallographic similarities
between copper and diamond.
Later, an independent YDB study by Tian et al.
(2011) confirmed the discovery of cubic YDB NDs
at Lommel, Belgium, in the charcoal-rich YDB
layer in the upper part of a layer that is known
regionally as the Usselo Horizon. The intersection
between the Usselo layer and regional overlying
cover sands has been long recognized as represent-
ing the onset of the YD climate change (Van Geel
et al. 1989). At Lommel, cubic NDs were embedded
in carbon particles but with no other ND polytypes,
and no NDs were observed above or below the YDB
layer. As with previous studies, the authors did not
examine bulk sediment for NDs. Tian et al. (2011)
concluded that the NDs alone did not represent
indisputable evidence for a cosmic impact, but they
did not exclude one.
Israde-Alca´ntara et al. (2012b)usedmultiplean-
alytical techniques to demonstrate that the YDB
NDs from Lake Cuitzeo, Mexico, are cubic NDs,
n-diamonds, i-carbon, and lonsdaleite-like crystals.
Israde-Alca´ntara et al. (2012b) also identified sev-
eral problems and limitations of the study by Daul-
ton et al. (2010), who reported an absence of YDB
NDs in carbon spherules at Murray Springs and
Arlington Canyon. First, Daulton et al. (2010)
searched for and failed to find NDs within carbon
spherules at Murray Springs, but neither Firestone
et al. (2007) nor Kennett et al. (2009a) reported find-
ing carbon spherules at that site, making the related
absence of NDs unsurprising. Our investigations
showed that carbon spherules are most common in
regions having conifer trees at 12,800 cal BP, not
in scrubby grasslands, as existed at Murray Springs
at that time (Haynes and Huckell 2007). Second, at
both sites Daulton et al. (2010) searched for NDs
in charcoal, which has never been reported by any
workers to contain NDs. Third, Daulton et al.
(2010) did not examine bulk sediment, the only
source of NDs at Murray Springs reported by Ken-
nett et al. (2009a).
Kennett et al. (2009b)reportedNDsincarbon
spherules at Arlington Canyon, California; Daulton
et al. (2010) found no NDs there either, but there
was a major flaw in their sample acquisition. The
same coauthors of Daulton et al. (2010) claimed, in
Pinter et al. (2011, p. 254), to have acquired their
samples from a location “identical or closely prox-
imal to the location” examined by Kennett et al.
(2009a). Contradicting that statement, Wittke et al.
(2013) noted that the Universal Transverse Mer-
cator coordinates of their sampling sites show con-
clusively that their purported continuous sequence
was actually collected as four separate discontin-
uous sections, separated by up to 7000 m horizon-
tally from the sampling location of Kennett et al.
(2009a, 2009b). Therefore, Scott et al. (2010) did not
sample the YDB at the location studied by Kennett
et al. (2009a)anddidnotacquireadated,contin-
uous profile across the YDB at any Arlington
Canyon location. These mislocated sediment sam-
ples collected by Scott et al. (2010) were subse-
quently used in several different studies by the
same group of authors (Daulton et al. 2010; Scott
et al. 2010; Pinter et al. 2011). Their incorrect strat-
igraphic locations apply to all those investigations,
explaining their inability to detect YDB NDs, cos-
mic-impact spherules, and ND-rich carbon spher-
ules at Arlington Canyon.
Daulton (2012) also questioned the identification
of lonsdaleite (hexagonal diamond), suggesting that
some particles exhibited in Kennett et al. (2009b)
appear to be graphene-graphane aggregates. Van
Hoesel et al. (2012), Madden et al. (2012), and Be-
ment et al. (2014) also reported finding graphene-
graphane clusters with diffraction patterns similar
to those of lonsdaleite. Boslough et al. (2012) sug-
gested that some of the reported lonsdaleite from
Lake Cuitzeo might instead be other minerals. We
discuss these points below in “Identification of
Lonsdaleite-Like Crystals.”
Daulton (2012) and Boslough et al. (2012) ques-
tioned whether YDB NDs are robust cosmic-impact
markers. However, cubic NDs are widely accepted
to have formed during the K-Pg impact event and
were not found in sediment before or after the event
(Carlisle and Braman 1991; Gilmour et al. 1992;
Hough et al. 1997, 1999). Those NDs are found at
six coeval sites across North America: two in Colo-
rado and one each in Mexico, Montana, and Al-
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478 C . R . K I N Z I E E T A L .
berta, Canada. The K-Pg NDs were reported to
range in size from 1 nm to 30 mm, whereas YDB
NDs are smaller, spanning a narrower range of 1
to 2.9 mm, perhaps because that older impact was
larger and more energetic than the YDB event.
Van Hoesel et al. (2012) observed cubic NDs
within particles of glass-like carbon at the Geldrop-
Aalsterhut site in the Netherlands. The NDs were
found in a few-centimeter-thick, charcoal-rich in-
terval at the upper boundary of the Usselo layer,
the top of which is widely accepted as representing
the onset of the YD cooling episode (Van Geel et
al. 1989). They reported NDs only in glass-like car-
bon in the bottom 1 cm of that interval and did not
examine bulk sediment for the presence of NDs.
Recently, Bement et al. (2014) discovered an
abundance peak in YDB n-diamonds (190 ppm) at
Bull Creek, Oklahoma, independently confirming
the discovery there of YDB NDs (100 ppb) by Ken-
nett et al. (2009a). They did not observe cubic NDs,
as Kennett et al. (2009a)did,andneithergroupob-
served lonsdaleite at Bull Creek. In addition, Be-
ment et al. (2014) observed an ND abundance peak
of similar amplitude to their YDB peak in two con-
tiguous samples of late Holocene surface sediments
(0–10 and 10–20 cm below surface). They suggested
that this younger ND peak may have been produced
by a nearby cosmic-impact event within the past
several thousand years. This discovery may corre-
late with that of Courty et al. (2008), who discov-
ered melt-glass and spherules at widely distributed
sites in Syria, Spain, and Peru, localities separated
by up to 13,000 km, as evidence for a 4000-yr-old
Northern Hemispheric impact event. Bement et al.
(2014) concluded from sedimentological evidence
that the peak ND accumulations in the YDB and
younger strata did not result from changes in cli-
mate, deposition rates, lag deposits, or human site
usage. Their results refute the hypothesis that the
NDs simply resulted from cosmic influx that de-
posited them as a lag deposit at the YDB over an
extended interval of time (Haynes et al. 2010; Pin-
ter et al. 2011; Boslough et al. 2012). Instead, Be-
ment et al. (2014) concluded the evidence is con-
sistent only with cosmic-impact events.
In summary, abundant NDs within or near the
YDB layer have been reported by four independent
groups (Redmond and Tankersley 2011; Tian et al.
2011; van Hoesel et al. 2012; Bement et al. 2014).
In addition, NDs have been reported independently
in three conference presentations (at Indian Creek,
MT, by Baker et al. 2008; at Newtonville, NJ, by
Demitroff et al. 2009; and at Bull Creek, OK, by
Madden et al. 2012). These investigations indepen-
dently confirm the presence of an ND abundance
peak in the YDB layer, which has also been shown
to be associated with a diversity of other cosmic-
impact proxies. Research continues into the spe-
cific origin of the various YDB ND polytypes and
the presence of lonsdaleite.
Material and Methods
We now present a comprehensive summary of the
chemical processing methods that we used to ex-
tract and isolate NDs from terrestrial bulk sedi-
ments and glacial ice. This is followed by details
of the characterization, identification, and inter-
pretation of YDB NDs. The protocol here super-
sedes previous published versions for extracting
YDB NDs (Kennett et al. 2009a, 2009b; Kurbatov
et al. 2010; Israde-Alca´ntara et al. 2012b). Further
details are in appendix A.
Our protocol was adapted by one of us (S. S. Que
Hee) from the extraction procedure developed by
Huss and Lewis (1995), who used it to isolate pre-
solar NDs from meteorites. We found that the max-
imum yield of all types of NDs occurred after the
ammonium hydroxide extraction step and that sub-
sequent oxidation with perchloric acid destroyed
many crystals of n-diamonds and i-carbon and, pos-
sibly, some of the lonsdaleite-like crystals. This
was an advantage when analyzing cubic NDs but
amajordisadvantagefortheotherallotropes,which
were no longer present. Although the extraction
process remains difficult, exacting, and labor-
intensive, we have successfully extracted NDs
from hundreds of samples in or adjacent to the YDB
layer on three continents and in the Greenland Ice
Sheet, along with samples from the K-Pg impact,
Sudbury Crater, and the Tunguska airburst. Six in-
dependent groups have successfully used this pro-
tocol or a version of it (Baker et al. 2008; Demitroff
et al. 2009; Redmond and Tankersley 2011; Tian et
al. 2011; van Hoesel et al. 2012; Bement et al. 2014).
Preparing Sediment and Ice. From each sedimen-
tary sample collected, 500–1000 g of thoroughly
mixed dry bulk sediment was processed through a
clean, ultrasonicated !38-mmscreentoconcentrate
the fine, ND-bearing fraction. A minimum of 20–
150 g of the !38-mmfractionwasusedforextraction
of NDs, whereas the 138-mm-size fraction was not
used. Water was removed from bulk ice core sam-
ples by freeze-drying or by melting and evaporation
before chemical processing. This method extracts
unattached NDs within the sediment as well as any
NDs that may be contained inside any melt-glass
or small mineral aggregates. Great care was taken
to eliminate contamination by industrial cubic
NDs, and any such contamination is highly un-
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 479
likely, as indicated by the fact that NDs always
peak in the same layer that contains other markers.
Peaks of similar magnitude have never been found
outside the YDB layers.
Materials and Equipment. All solutions were pre-
pared with corresponding TraceMetal or Electron-
ics-grade chemicals and concentrated acids or ba-
ses. A detailed list of standard instrumentation and
equipment appears in appendix A.
Extraction and Purification. As many operations
as possible were performed at room temperature,
because temperatures above 200#C can cause non-
cubic types of NDs to gradually convert to other
forms of carbon, such as graphite. Also, adequate
rinsing and centrifugation are crucial for successful
purification of the ND-rich residues.
The YDB NDs contain surface carboxyl groups
(–COOH) formed in situ either during ND forma-
tion or during diagenesis while buried for 12,800
yr. These carboxyl groups are a key part of the ex-
traction process, because they allow the NDs to go
into suspension in basic solution, thus separating
from the non-ND minerals. However, these car-
boxyl groups are also subject to decarboxylation un-
der strongly acidic conditions and/or at elevated
temperatures. Therefore, it is vitally important to
extract any NDs into room-temperature basic so-
lution (pH 17) while they still contain the maxi-
mum density of carboxyl groups on their surfaces.
After the samples were pulverized and massed,
therefore, the first chemical step was extraction of
NDs, using room-temperature 0.1 M NaOH. Once
NDs were separated from the remaining sediment,
they were consolidated in solution acidified to a
pH of !2 with 9 M HCl.
Next, acidic dichromate oxidation (K
2
Cr
2
O
7
and
H
2
SO
4
) was used to remove the remaining intrac-
table organic components that might adhere to
NDs. Following dichromate oxidation, samples
were diluted with deionized water to lower solu-
tion density and were centrifuged. Supernatants
were discarded, and residues were rinsed repeatedly
with 0.1 M HCl. Some YDB residues were visible,
but most were detectable only by light microscope.
For non-YDB samples, often there were no residues
visible with a light microscope.
At this point, most non-ND minerals were either
left behind during basic extraction or oxidized by
the acidic dichromate. Any remaining silicates
were digested with 10 M HF/1 M HCl, and after
rinsing, samples were treated with 9 M HCl to de-
stroy fluorides. If necessary, the acidic dichromate
and hydrofluoric acid steps were repeated. Finally,
the samples were dried and weighed. The typical
result was a very small amount of whitish-gray res-
idue that contained amorphous carbon and, if pres-
ent, an assemblage of several types of NDs (cubic,
n-diamonds, i-carbon, and lonsdaleite-like crys-
tals). This was the last step performed if we chose
to examine all types of NDs.
If we chose to investigate only the cubic NDs,
an additional step was added to destroy the n-dia-
monds, i-carbon, and possibly lonsdaleite, thus
making it easier to identify the cubic NDs. To ac-
complish this, we added concentrated perchloric
acid (HClO
4
,70%),heatedthemixture,andthen
allowed the perchloric acid to evaporate to dryness.
After that, samples were rinsed several times with
0.1 M HCl and centrifuged. Once dried, the ex-
tracted ND residues were ready for further analysis.
The acid extraction process commonly yielded very
little residue that was nearly invisible to the naked
eye inside the centrifuge tubes and often was de-
tectable only by light microscope. For non-YDB
samples, there were typically no residues visible
even with a light microscope.
Early Developmental Studies. To test this protocol
at the HF step, we used synthetic cubic NDs from
PlasmaChem (PL-D-G-1g; avg. cluster size 4 nm;
NDs usually 2nm)ataconcentrationcorrespond-
ing to 1000 ppm in 10 g of sediment. When the
nitric acid was substituted for HCl, the HF/HNO
3
digestion step allowed recovery of 70%–80% by
weight. The soluble phase contained 20%–30% of
NDs by weight, and HCl acid-washing conditions
resulted in quantitative recoveries in the solid res-
idue at each such step. The recovery of spiked cu-
bics up to the perchloric acid step varied between
70% and 80% in these preliminary experiments.
The major step responsible for the variation was
the flocculation step.
To determine the efficacy of the perchloric acid
extraction step, we conducted severalexperiments.
When 10 mg of synthetic cubic NDs was subjected
to the perchloric acid processing step, 81% "5%
was recovered by weight as unaltered cubic NDs.
Transmission electron microscopy (TEM) con-
firmed the presence or absence of NDs in all these
experiments, which confirmed that extraction of
NDs with this protocol has a high success rate.
NDs from Carbon Spherules and Amorphous
Carbon. The NDs were not extracted from carbon
spherules; instead, the spherules were crushed to
fine fragments and placed on a TEM grid, as de-
scribed in detail in appendix A. Tian et al. (2011)
and van Hoesel et al. (2012) reported YDB NDs in
flakes of amorphous carbon or glass-like carbon,
and our general protocol for carbon spherules also
applies to NDs within these other forms of carbon.
Preparation of TEM Grids for Analyzing NDs. Cur-
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480 C . R . K I N Z I E E T A L .
rently, we use 200- to 400-mesh TEM grids of gold
or molybdenum with ultrathin carbon film (3 nm
thick) over holey carbon. It is important to note
that because ultrathin films are approximately as
thick as the NDs and other nanoparticles, they
have the least effect on energy dispersive X-ray
spectrometry (EDS) and other measurements, mak-
ing their use essential for obtaining the best anal-
yses. We avoided films that have large open holes
(holey carbon) because the NDs are much smaller
than the holes.
Some earlier ND work (Kennett et al. 2009a,
2009b; Kurbatov et al. 2010) was conducted on cop-
per grids, which were discontinued because of the
similarity between the spacings of crystallographic
planes (d-spacings) of copper and some NDs (Daul-
ton et al. 2010). Those early samples on copper grids
were subsequently reanalyzed on gold or molyb-
denum grids and with additional analytical tech-
niques, such as EDS and energy-filtered TEM
(EFTEM) that can differentiate carbon from copper
particles. The results confirmed that the use of cop-
per grids, although suboptimal, did not lead to the
misidentification of YDB NDs. In addition, al-
though silicon films are preferable to carbon films
for investigating carbon objects, we have discon-
tinued their use because they are less stable under
ahigh-voltageelectronbeam.
To prepare a TEM grid, we first placed NDs into
suspension by pipetting just 1 or 2 drops of am-
monium hydroxide (NH
4
OH), ethyl alcohol, or
deionized water into the vial and stirring the ND-
rich mixture. Then we pipetted the drop onto the
grid and dried it. For further details of preparing
grids, see appendix A.
Experimental Methods: Electron Microscopy and
Spectroscopy. Sample residues were examined
with high-resolution TEM (HRTEM), scanning
TEM (STEM), electron energy-loss spectroscopy
(EELS), selected-area electron diffraction (SAD), and
EDS. To accomplish that, we used an FEI 300-kV
field emission gun Titan equipped with a Super
Twin objective lens, a spherical-aberration-image
corrector, an EDAX energy-dispersive spectrome-
ter, a high-angle annular dark field (HAADF) de-
tector, and a Tridiem Gatan imaging filter. For all
of the experiments, the instrument was operated at
300 kV. The TEM detectors were calibrated for ac-
curacy with commercial cubic diamond and gold
standards (Ted Pella #646). Fast Fourier Transform
(FFT) analyses of the HRTEM images and the anal-
yses of the EELS data were performed with Gatan
Digital Micrograph. Occasionally, JEOL 1200EX II
and JEOL TEM 1210 transmission electron micro-
scopes were operated at 80 kV to acquire images
with higher contrast and to investigate nanoparti-
cles that vaporized at temperatures generated by
the higher voltages of the Titan.
Difficulties in Identifying NDs. The extraction
process detailed in this contribution yields a resi-
due that contains amorphous carbon, resistant min-
erals, and NDs, when present, but there are tech-
nical difficulties in fully characterizing this
material. For example, the protocol does not re-
move minor amounts of non-ND crystals, includ-
ing quartz, rutile, and zircon. Typically, NDs rep-
resent !50% of the residue, and the remaining
non-ND residue can mask the NDs, thus making
them difficult to identify. In addition, there are in-
herent difficulties and uncertainties in correctly
identifying tiny crystals !2 nm in diameter. Fur-
thermore, multiple ND polytypes are often inter-
mixed, making differentiation of individual poly-
types difficult.
Quantification of NDs. Accurate quantification of
ND abundances in a sample is difficult, because
the volume of NDs present is typically minuscule
and the NDs are difficult to isolate from amorphous
carbon. We addressed this problem by adapting
methods used by various researchers to semiquan-
tify abundances of other kinds of particles, such as
aciniform carbon (a form of soot), charcoal, fora-
miniferal species, and various plant microfossils.
We developed an 11-point scale (0% to 100%) for
estimating the abundances of NDs at parts-per-bil-
lion to parts-per-million levels in both the ex-
tracted residues and carbon spherules (see “Quan-
tification of NDs” in app. A; fig. A1; app. C). The
abundance values presented here supersede previ-
ously published values.
Results and Discussion
Regional Setting. The YDB ejecta field contains
a variable assemblage of cosmic-impact markers,
including NDs, cosmic-impact spherules, carbon
spherules, and high-temperature melt-glass. The
field spans an area of 50 million km
2
across four
continents, with no known limits (Wittke et al.
2013). For this study, we investigated YDB NDs at
22 sites in 10 countries on three continents, and
independent researchers conducted six studies, for
atotalof24sites(g.1).Thirteensitesareinthe
United States, two in Canada, two in the Nether-
lands, and one each in the Greenland Ice Sheet
(Denmark), Belgium, Germany, Mexico, Spain, Sy-
ria, and the United Kingdom. These 24 sites occur
across a remarkably diverse range of geologic set-
tings, including polar ice, glacial till, mountain
lakes, caves, coastal canyons, desert dry washes,
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 481
and alluvial terraces, with altitudes varying from
near sea level to 11800 m. This wide diversity in-
dicates that geologic setting has no effect on the
presence of YDB NDs, as also concluded by Bement
et al. (2014). Details on site setting, geological in-
formation, and dating are in tables D2, D3. More
details for most sites are in Bunch et al. (2012) and
Wittke et al. (2013).
Dating and Age-Depth Models. We present new ra-
diocarbon dates for three sites (Lake Cuitzeo, Mex-
ico; Lingen, Germany; and Santa Maira, Spain), and
we have generated new age-depth models for Ar-
lington Canyon (fig. B1) and Lake Cuitzeo (figs. B2,
B3). We present ND data for 15 new sites, for which
site details, stratigraphic information, and dating
are provided in appendix B and tables D2, D3. Of
the 24 sites investigated, 18 (75%) have either di-
rect dates or age-depth models at sufficient chro-
nological resolution to confirm correlation with
the YDB. Three others have been indirectly dated
via lithologic and isotopic stratigraphy, archaeolog-
ical context, and age-depth modeling, and the re-
maining three sites lack dates directly from the
YDB but have consistent extrapolated ages based
on dated materials from near the boundary layer.
The dates for a few of these sites have been chal-
lenged. For example, Blaauw et al. (2012) ques-
tioned the age-depth model for the Lake Cuitzeo
sediment core in Israde-Alca´ntaraetal.(2012b) and
proposed that the YDB layer is up to 2000 yr older
than the modeled age. Israde-Alca´ntara et al.
(2012a) countered that the modeled age is the only
one consistent with palynological and climatolog-
ical records from this sequence and several sites
located in Central and South America. To further
test the age model, we acquired a new accelerator
mass spectrometry
14
C date (NOSAMS-71325:
10,550 "35 RCYBP, 12,897 "187 cal BP) on or-
ganic sedimentary carbon collected above the YDB
layer in a nearby exposed shoreline sediment se-
quence, lithologically correlated with the lake core.
This helps constrain the age of the ND-rich layer
and demonstrates that the model previously pub-
lished in Israde-Alca´ntara et al. (2012b) is correct
(table D3; figs. B2, B3).
Boslough et al. (2012) questioned the age deter-
mination for the YDB at the Gainey, Michigan, site,
on the basis of a modern date acquired for a YDB
carbon spherule. That date replicated a modern
date previously reported for the same stratum of
the Gainey sequence (Firestone 2009). Also, Ives
and Froese (2013) questioned the inferred YDB age
for carbon spherules at the Chobot site in Canada,
also on the basis of a young radiocarbon date from
Firestone (2009). Nevertheless, the archaeological
context argues against a modern age for these near-
surface layers. At both the Gainey and Chobot
sites, the inferred YDB layers contain glassy and
magnetic cosmic-impact spherules, as well as car-
bon spherules, each filled with millions of NDs (see
“TEM, SAD, and Scanning Electron Microscopy of
NDs in Carbon Spherules” below). This impact evi-
dence is associated with large numbers of tempo-
rally diagnostic, Clovis-era artifacts that are found
near the surface but date within a range of 13,250–
12,800 cal BP (Waters and Stafford 2007). Further-
more, the span of an OSL date (12,360 "1230 cal
BP) for the same Gainey layer includes the onset
of the YD at 12,800 cal BP and is not modern in
age. Thus, on the basis of available evidence, these
young radiocarbon dates do not accurately reflect
the age of the inferred YDB layers at these sites.
Firestone (2009) presented several possibilities to
explain these age discrepancies, and the most likely
is the effects of bioturbation. At some sites, we
observed distinctive root casts, formed from large
taproots of trees that penetrated the YDB layer after
the impact event occurred. After those roots de-
cayed or burned, the resulting cavity filled with
sediment containing younger charcoal and carbon
spherules that mixed with the older carbon mate-
rial. Because this is a common occurrence where
the YDB is shallow, radiocarbon dating is unreliable
for such sites and OSL dating is preferred (Bunch
et al. 2012), as indicated by the older OSL date for
the Gainey site. No matter the cause, the ages of
these two sites remain poorly constrained. Nev-
ertheless, 18 of the 24 sites with the same YDB
markers are well dated, suggesting that the YDB
layer is correctly identified at Gainey and Chobot
(table D3).
Later, van Hoesel et al. (2012, p. 7652) suggested
that NDs in the Netherlands at the Aalsterhut site
are “two centuries younger than the diamonds re-
ported by Kennett et al.” (2009b)andthereforeare
from an unrelated event. They concluded this on
the basis of an apparent age discrepancy between
the mean age of the ND-rich layer at their site and
mean age of the Arlington Canyon site in Califor-
nia. However, they overlooked the fact that the
date for the Aalsterhut site fully overlaps those for
many other YDB sites, including Murray Springs.
To test their hypothesis, we performed Bayesian
analysis (Bronk Ramsey 2009) and x
2
testing (Ward
and Wilson 1978) on the Arlington Canyon radio-
carbon dates. Both methods indicate that the Ar-
lington Canyon radiocarbon dates have nonnormal
distribution and thus are unsuitable for averaging
(fig. B1). Bayesian analysis is particularly useful in
detecting outlier dates (nonnormal distribution),
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482 C . R . K I N Z I E E T A L .
Figure 1. Map showing 24 sites containing Younger Dryas Boundary (YDB) nanodiamonds. The solid line defines
the current known limits of the YDB field of cosmic-impact proxies, spanning 50 million km
2
(Wittke et al. 2013),
including the study of Mahaney et al. (2010) in Venezuela (open circle). Numbered sites are from this study: (1) Lake
Cuitzeo, Mexico (Israde-Alca´ntara et al. 2012b); (2) Daisy Cave, California; (3) Arlington Canyon, California (Kennett
et al. 2009b); (4) Murray Springs, Arizona (Kennett et al. 2009a); (5) Lindenmeier, Colorado; (6) Bull Creek, Oklahoma
(Kennett et al. 2009a); (7) Blackville, South Carolina; (8) Topper, South Carolina (Kennett et al. 2009a); (9) Kimbel
Bay, North Carolina; (10) Newtonville, New Jersey; (11) Melrose, Pennsylvania; (12) Sheriden Cave, Ohio; (13) Gainey,
Michigan (Kennett et al. 2009a); (14) Chobot site, Alberta, Canada (Kennett et al. 2009a); (15) Lake Hind, Manitoba,
Canada (Kennett et al. 2009a); (16) Kangerlussuaq, Greenland (Kurbatov et al. 2010); (17) Watcombe Bottom, Isle of
Wight, United Kingdom; (18) Lommel, Belgium; (19) Ommen, Belgium; (20) Lingen, Germany; (21) Santa Maira,Spain;
(22) Abu Hureyra, Syria. In addition, independent researchers have reported NDs at six sites, indicated by letters,
four of which are in common: (a) Indian Creek, Montana (Baker et al. 2008); (b) Bull Creek, Oklahoma (Madden et
al. 2012; Bement et al. 2014); (c) Sheriden Cave, Ohio (Redmond and Tankersley 2011); (d) Newtonville, New Jersey
(Demitroff et al. 2009); (e) Lommel, Belgium (Tian et al. 2011); (f) Aalsterhut, Netherlands (van Hoesel et al. 2012).
A color version of this figure is available online.
including those that result from the old-wood ef-
fect, in which the date for charcoal or wood from
along-livedtreecanleadtotheerroneousconclu-
sion that the stratum in which the charcoal was
found is much older. Bayesian analysis rejected 14
of 16 Arlington Canyon dates as being outliers, con-
sistent with the observation that local tree species
have life spans of up to 1300 yr (see “Arlington
Canyon, California” in app. B). After adjusting for
the old-wood effect, OxCal modeled the YDB age
for Arlington Canyon as 12,748 "46 cal BP (OxCal,
ver. 4.2.3, IntCal-13; Bronk Ramsey 2009). This is
statistically identical to the modeled YDB date for
Aalsterhut of 12,746 "12 cal BP (10,870 "15
RCYBP; van Hoesel et al. 2012). These results con-
tradict the hypothesis that the ND-rich layer at
Aalsterhut is 200 yr younger than the ND-rich YDB
layer at Arlington Canyon. Furthermore, van
Hoesel et al. based their 200-yr difference on the
mean ages of the two sites, but the standard de-
viation must be considered, and using only mean
ages is inappropriate. We conclude that van Hoesel
et al. (2012) discovered the YDB layer at Aalsterhut.
Bayesian analysis shows that the ages of all 18 well-
dated YDB sites fall within 1 standard deviation of
the YDB layer at 12,800 "150 cal BP, including
Aalsterhut and Arlington Canyon (table D3). None
of those 18 sites is 200 yr older than Aalsterhut.
Van Hoesel et al. (2014) also questioned whether
the YDB proxies are synchronous with the onset of
the YD climatic episode, which is widely accepted
to have occurred abruptly. For example, in the
NGRIP ice core, Steffensen et al. (2008) found that
the YD onset occurred within a span of 1.5 yr, and
Brauer et al. (2008) reported a similar narrow span
of 1 yr in varved European lake records. The
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 483
Greenland Ice Core Chronology 2005 (GICC05;
Rasmussen et al. 2006) found the mean age of the
YD onset to be 12,896 "138 before 2000 AD (b2k;
13,034–12,758), and the GISP2 ice model (Meese et
al. 1997) placed it at 12,892 "260 b2k (13,152–
12,632). The YDB ages for 20 of 24 sites (83%) in
table D3 fall within the ice core age ranges for the
onset of the YD climatic episode, suggesting a close
relationship between the YDB and the YD onset.
Most importantly, a major peak in impact-related
platinum in the GISP2 ice core occurred precisely
at the onset of the YD climatic episode (Petaev et
al. 2013), strongly indicating that the YDB cosmic-
impact event and the onset of the YD episode are
synchronous.
The YDB hypothesis posits that only one impact
occurred, producing coeval, above-background
peaks in NDs, iridium (Firestone et al. 2007), plat-
inum (Petaev et al. 2013), osmium (Wu et al. 2013),
high-temperature melt-glass (1730#to 12200#C;
Bunch et al. 2012), and high-temperature magnetic
spherules (11500#C; Wittke et al. 2013). Others
have proposed various age models for deposition of
the YDB proxies. The first counterexplanation is
that YDB proxies resulted from multiple, unrelated,
natural mechanisms that coincidentally occurred
near 12,800 cal BP (Pinter et al. 2011; Boslough et
al. 2012; van Hoesel et al. 2014). To investigate that,
our group and others have measured marker abun-
dances in several stratigraphic profiles that span as
much as the past 30,000 yr. These proxies reached
maximum abundances only in the YDB layer and
are not known to peak individually or collectively
anywhere else in that span, making the YDB highly
unusual. In the second scenario, the YDB proxies
were deposited over several centuries, resulting
from multiple discrete cosmic-impact events.
However, current understanding of impact dynam-
ics cannot explain how such a scenario could occur
over such a span. In the third scenario, the YDB
proxies were deposited during a span of up to sev-
eral decades. Such a situation could occur if the
debris field of a fragmented comet or asteroid was
oblique to or wider than Earth’s diameter upon im-
pact. In such a case, some objects would have en-
countered Earth at an oblique angle and could have
assumed orbits that decayed over a few years to
decades, producing multiple smaller impacts (Faw-
cett and Boslough 2002; Petaev et al. 2013). The
fourth and most plausible scenario, the one most
consistent with our data, is that only one hemi-
spheric impact event occurred. This is supported
by the platinum record in GISP2, which forms a
single, brief, coherent abundance peak, the only one
within the 280-yr interval investigated.
Abundance and Stratigraphic Distribution of NDs.
Crystal morphologies vary from angular to rounded
and from monocrystalline to twinned, and ND di-
ameters average 3–4 nm (range: 1 nm–2.9 mm), with
most measuring between 1 and 20 nm, a typical
size for detonation-formed NDs (Wen et al. 2007).
The quantification method discussed above was
used to estimate abundances of NDs and revealed
concentrations in carbon spherules of 10–3680 ppb
(mean: 755 ppb) and in bulk sediment of 11–494
ppb (mean: 200 ppb). For carbon spherules, 111 of
153 samples investigated (73%) contained no de-
tectable NDs, and for sediment, 57 of 87 (66%) sam-
ples had no evident NDs, comparable to the null
results of Bement et al. (2014). Appendix A dis-
cusses quantification, figure 2 shows abundance
peaks in NDs, and table D4 lists the stratigraphic
abundances of NDs for 22 sites. Table D4 also lists
abundances of cosmic-impact spherules and melt-
glass for 16 sites; the other six sites have not yet
been examined for those proxies. All sites exhibit
sharp ND abundance peaks at the YDB, with very
few NDs in the strata above and below (fig. 2). For
some sites, the peaks are broader, with elevated
abundances of NDs in several contiguous samples.
These secondary peaks most likely result from bio-
turbation and wind-and-water action that redistrib-
uted the NDs upward and/or downward.
Identification and Taxonomy of YDB NDs
Overview. Unknown nanoparticles were inves-
tigated with multiple analytical techniques; a
nanoparticle was conclusively identified as an ND
if several basic properties were documented: first,
the nanoparticle is composed only of carbon; sec-
ond, it has a crystalline structure; and finally, the
d-spacings match those of an ND polytype. Al-
though it is unnecessary to use all of the analytical
procedures described below for every particle, at a
minimum, we used EDS to determine elemental
composition and HRTEM, SAD, and/or FFT to de-
termine crystalline structure for all nanoparticles
imaged in this contribution. These analyses were
strengthened by use of EELS and EFTEM to assist
with determining elemental compositions and to
investigate the interatomic bonding typical of car-
bon (sp
2
and/or sp
3
).
Electron Microscopy (TEM, HRTEM, and STEM).
The STEM mode (HAADF, dark field) was typically
used to investigate candidate nanoparticles, but the
quality of the images was often degraded by scat-
tering of electrons by the amorphous residue and
by contamination of the grid by vaporized carbon.
The TEM and HRTEM modes (bright field) typi-
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Figure 2. Abundances of nanodiamonds (NDs; ppb) for 22 Younger Dryas Boundary (YDB) stratigraphic sections
plotted by depth (cm below surface). Most of the six independent studies did not quantify NDs at or near the YDB
and are not represented here. Horizontal bands represent thicknesses of samples containing YDB proxies. Solid lines
represent ND abundances (ppb), shown on the X-axis. ND abundances were estimated with an 11-point semiquan-
tification scale of relative values ranging from 0% to 100% (see “Quantification of NDs”). CS pNDs extracted from
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 485
carbon spherules; SED pNDs from bulk sediment; “surface” indicates ground surface for eight sites; no NDs were
observed in these surface layers. Abundances for NDs, carbon spherules, and cosmic-impact spherules are listed in
table D4, available online. Data are from Kennett et al. (2009a, 2009b), Kurbatov et al. (2010), and Israde-Alca´ntara
et al. (2012b). A color version of this figure is available online.
cally produced clearer images of NDs located in
residue, thus strengthening analyses of crystallin-
ity and lattice spacings.
Figure 3 illustrates the typical progression nec-
essary to identify NDs. First, extracted material
from Murray Springs and Lake Cuitzeo produced
STEM images that show thousands of rounded-to-
subrounded, nanosized particles (fig. 3Aand 3B, re-
spectively). At this point, it was unknown whether
they were amorphous or crystalline. Next, an
HRTEM image (fig. 3C) revealed the crystalline
structure of NDs (“ND”), among a background of
amorphous carbon and strand-like carbon ribbons
(“CR”) that are commonly present in the diamond-
rich residue. Finally, an HRTEM image of a carbon
nanocrystal (fig. 3D)displayedlatticespacingsof
2.06 A
˚,consistentwith(111)planesforcubicdia-
mond (table D1), when viewed along the [110] zone
axis. Additional testing typically was performed on
these nanocrystals, as discussed below.
SAD and FFT of HRTEM. The SAD image from
Murray Springs (fig. 4A)displaysaringpatternof
collective d-spacings from multiple crystals, and in
this case, all eight visible reflections match those
of cubic NDs. Values for graphene and graphane are
similar to those for six of those reflections, but the
(400) and (551) reflections are not present in those
other crystals (table D1). Their absence in SAD pat-
terns for graphene and graphane makes those min-
erals easily detectable, thus eliminating the pos-
sibility of misidentification. By themselves, SAD
patterns are insufficient to identify NDs, and so
further investigations, such as those using HRTEM,
FFT, EDS, and EELS, were performed on thesenano-
particles to confirm that they are NDs and not
some other mineral. The FFT of an HRTEM image
of multiple nanocrystals (fig. 4B) shows three ring
reflections that match the SAD pattern for cubic
NDs. The FFT of an HRTEM image of a single
nanocrystal (fig. 4C)displays(111)-and(220)-type
spot reflections consistent with a single cubic di-
amond viewed along the [110] zone axis. Figures 5
and 6 show TEM, HRTEM, and SAD patterns for
NDs found in bulk sediment and carbon spherules
from sites on three continents. Results from 10
other sites are shown in figures C1–C6.
EDS. ASTEMimagefromLakeCuitzeo(g.7A)
shows a nanoparticle field with the specific area of
investigation boxed near the center. The SAD pat-
tern of that boxed area (fig. 7B)exhibitsdiffraction
rings characteristic of i-carbon. The EDS analysis
of the boxed area (fig. 7C)indicatedacarboncon-
centration of 198% as well as low amounts of ox-
ygen and a weak signal from the gold grid, but no
other elements. Because this analysisencompasses
nanocrystals, the grid film (3-nm thick), and sur-
rounding amorphous carbon, the elemental per-
centages for the nanoparticles are inexact but are
dominantly carbon. When other mineral grains
were encountered, e.g., quartz, rutile, and zircon,
they were easily identifiable with EDS. Another
STEM image (fig. 7D)showsaclusterofangular
synthetic cubic NDs (97% pure 4-nm clusters from
PlasmaChem) with no observable amorphous car-
bon; the box indicates the region being analyzed.
An SAD pattern (fig. 7E)exhibitsdiffractionrings,
indicating that the nanoparticles are cubic NDs,
with no diffraction rings of other minerals. The
EDS spectrum of the commercial diamonds in fig-
ure 7Fshows 197% carbon, which closely matches
the EDS of YDB NDs in figure 7C,withasimilarly
high abundance of carbon.
EELS. The EELS analyses were performed to de-
termine whether selected nanoparticles are carbon
and whether they display the correct atomic bond-
ing for diamond. This is diagnostic for distinguish-
ing cubic NDs and lonsdaleite-like crystals from
other forms of carbon. The EELS technique is less
useful for differentiating n-diamonds, i-carbon,
graphite, and other carbon allotropes from each
other, since these produce similar spectra. To dif-
ferentiate the various carbon polytypes, it is also
necessary to acquire SAD patterns and FFTs of
HRTEM images.
The Murray Springs EELS spectrum, known as a
core-loss spectrum (fig. 8A), displays the typical
shape for cubic diamond (Peng et al. 2001). The
edge is well above background, indicating that
j
the nanoparticles are carbon. The small edge is
p
representative of lower-order sp
2
bonding, as found
in graphite, graphene, graphane, and amorphous
carbon. In this case, the peak most likely represents
the carbon grid film and amorphous carbon in
which the NDs are embedded. The two peaks at
300 and 310 eV with a trough between them rep-
resent the characteristic signature of cubic dia-
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486 C . R . K I N Z I E E T A L .
Figure 3. Three techniques for identifying candidate nanodiamonds (NDs). A,B,Scanningtransmissionelectron
microscopy images of clusters of NDs from Murray Springs, Arizona (Younger Dryas Boundary [YDB]: 426 ppb of
NDs at 46.5 cm below surface [cmbs]; A), and Lake Cuitzeo, Mexico (YDB: 493 ppb at 280 cmbs; B). C, Bright-field
high-resolution transmission electron microscopy (HRTEM) of ND-rich residue from Murray Springs. CR pcarbon
ribbon. D, HRTEM image of a rounded cubic ND at Lake Cuitzeo. Parallel lines represent {111}-type lattice planes
(2.06-A
˚spacing), as viewed along the [110] zone axis. A color version of this figure is available online.
mond with sp
3
bonding. This pattern definitively
eliminates the possibility that these nanocrystals
are graphite, graphene, and graphane.
The EELS plot in figure 8Bis of synthetic com-
mercial cubic diamond (PlasmaChem) and closely
resembles the YDB spectrum. Note that the peak
p
is absent in this case, because of the lack of em-
bedding amorphous carbon matrix in the commer-
cial diamonds. The Murray Springs EELS spectrum
(fig. 8C)indicatesamixofmostlyn-diamondsand
i-carbon and is significantly different from the EELS
spectrum for the synthetic cubic diamond. In this
case, a peak is present, indicating some sp
2
bond-
p
ing, consistent with n-diamond, which is reported
to contain approximately 5% sp
2
and 95% sp
3
bond-
ing (Peng et al. 2001). The absence of a peak-and-
trough pattern (arrows in fig. 8A,8B) indicates that
the nanoparticle is not a cubic ND. This spectrum
is a close match for previously published spectra
for n-diamond and i-carbon (curved lines above the
spectra) but is a poor match for graphite, graphene,
and amorphous carbon, which typically display
peaks with greater amplitude, indicating pro-
p
portionately more sp
2
bonding. Thus, low-ampli-
tude peaks can be used to infer that a particle
p
is likely a diamond polytype.
EFTEM. We used EFTEM in some cases as an
elemental mapping technique to investigate the
spatial distribution of carbon and to examine its
relative atomic bonding (sp
2
and sp
3
), as was first
used for YDB NDs by Tian et al. (2011). Figure 9A,
from the YDB layer in Lake Cuitzeo, is called a
“zero-loss” image, exhibiting various lighter nano-
crystals embedded in the grayer amorphous carbon
residue, itself superimposed on the darker amor-
phous carbon TEM grid film, marked “AC.” This
image is displayed in reverse contrast for clarity.
Using HRTEM and FFT, we identified and labeled
the larger nanocrystals by polytype; in this view,
n-diamonds, i-carbon, and cubics have a ratio of
3:1:1. There is also one lonsdaleite-like crystal,
with a relative abundance that is atypically high in
this case. Next, we generated a “jump ratio” image
(fig. 9B) by comparing postedge energies character-
istic of carbon ( edge) with background energies
j
(260 eV). The resulting map displays bonding dif-
ferences for the larger particles, whose bright gray-
to-white contrast indicates the presence of some
amount of sp
3
bonding that is characteristic of NDs
but not of graphite, graphene, and graphane. The
black-colored areas (AC) represent the TEM grid
film, composed of amorphous carbon with no sp
3
bonding.
The brighter areas between particles indicate the
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 487
Figure 4. Two techniques for identifying cubic nanodiamonds (NDs). A,Selected-areaelectrondiffractionpattern
of cubic NDs from Murray Springs, with d-spacings (Younger Dryas Boundary: 426 ppb at 46.5 cm below surface). B,
Fast Fourier transform (FFT) of cubic NDs from Murray Springs; C, FFT of single cubic ND from Murray Springs,
viewed along the [110] zone axis. A color version of this figure is available online.
presence of small, sub-nanometer nanoparticles
displaying sp
3
bonding, and this observation, along
with the visible whitish-gray color of most resi-
dues, indicates that there is very little black, amor-
phous carbon present. Instead, the residue between
NDs appears to consist of diamond-like nanocrys-
tals arranged in short-range ordering that causes
them to appear amorphous. It is possible that these
are diamondoids, which are cage-like, ultrastable,
saturated hydrocarbons (de Araujo et al. 2012),
whose carbon-carbon lattice framework is largely
identical to a portion of the cubic ND lattice. Dia-
mondoids are found in hydrocarbon and coal de-
posits; they are nearly as hard as diamonds; each
diamondoid typically includes from 10 to 30 carbon
atoms; they are composed almost entirely of sp
3
-
bonded carbon (de Araujo et al. 2012); and diamon-
doid powder can be visibly whitish to clear (Schoell
and Carlson 1999). Diamondoids compare favora-
bly to most of the crystals in the extracted residue,
which also are dominantly carbon, have sp
3
bond-
ing, produce a diffuse SAD pattern because of their
small size, and are optically clear to white. Because
both n-diamonds and diamondoids have been found
in petroleum deposits related to the K-Pg, one
might speculate that something similar happened
during the YDB impact, especially if an impact took
place in deep, petroleum-rich offshore sediments.
More work is necessary to determine the nature
and identity of these small nanoparticles, but they
may be a clue to the YDB ND formation process.
The NDs in figure 9Btypically are brighter
around their edges but somewhat darker in their
centers. This variability highlights a disadvantage
of using EFTEM, which works best with thin layers
of NDs and/or amorphous carbon residue. Because
the fraction of electrons that undergo a single scat-
tering event in a thick area is less than that in a
thinner area, the jump ratio map shows a stronger
EFTEM signal in the thin areas, even though both
areas are equally populated by NDs.
Identification of n-Diamonds and i-Carbon. The
YDB layer contains two diamond-like polytypes, n-
diamonds and i-carbon, that were first synthesized
in the laboratory (Wen et al. 2007 and references
therein). Outside of the laboratory, face-centered
cubic NDs (another name for n-diamonds) were
first reported within carbon spherules from near-
surface sediments of unknown age across northern
Europe by Ro¨ sler et al. (2006). Later, both n-dia-
monds and i-carbon were found in the YDB layer
(Kennett et al. 2009a) and the K-Pg layer (Bunch et
al. 2008, 2009).
The YDB n-diamonds display the same d-spac-
ings as cubic NDs, except for the added presence
of so-called “forbidden” reflections evident in SAD
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488 C . R . K I N Z I E E T A L .
Figure 5. Transmission electron microscopy images (in reverse contrast for clarity; top) and selected-area electron
diffraction patterns (bottom) of nanodiamonds from three continents. A,B, n-Diamonds from sediment (Sed) at Abu
Hureyra, Syria (Younger Dryas Boundary [YDB]: 443 ppb at 405 cm below surface [cmbs]). C,D, n-Diamonds in carbon
spherules (CS) at Santa Maira Cave, Spain (YDB: 38 ppb at 3.5 cmbs). E,F, n-Diamonds from sediment at Lindenmeier,
Colorado (YDB: 143 ppb at 101 cmbs). A color version of this figure is available online.
patterns and FFTs of HRTEM images (table D1).
The lattice planes that produce these reflections are
present in both cubic and n-diamonds, but as a re-
sult of destructive interference, the reflections are
typically invisible in cubic NDs, hence the term
“forbidden.” These reflections may become visible
in cubics for several reasons: first, because of dou-
ble diffraction caused by the twinning; second, as
aresultofflawscausedbytheoccasionalsubsti-
tution of other elements for carbon atoms; and
third, because of incomplete unit cells at the edge
of the crystal. Thus, it is possible that n-diamonds
are actually twinned cubic NDs.
A TEM image from Murray Springs (fig. 10A) ex-
hibits more than 100 NDs that are tilted !30#from
normal in the microscope. A second TEM image
(fig. 10B)showsthesameNDs,buttiltedthrough
a 45#arc to "15#.Notethatcorrespondingobjects
appear similar in both images (e.g., particles 1–4),
indicating that they all are rounded to subrounded
and not planar. An SAD pattern of the same objects
(fig. 10C) indicates that these are n-diamonds.
SAD, FFT, and HRTEM for n-Diamonds and i-
Carbon. An SAD pattern from Murray Springs (fig.
11A)displayssevenlatticespacingsofn-diamonds
(table D1); EDS analyses confirmed these particles
to be composed of carbon. The FFT of an HRTEM
image (fig. 11B) shows five d-spacings of a single n-
diamond, and the HRTEM image of the same n-
diamond (fig. 11C)showsthreevaluesrepresenting
two lattice planes, of which the 1.78-A
˚plane is a
forbidden reflection in cubic NDs. The SAD pattern
for Lake Cuitzeo material (fig. 11D)displaysthe
first seven lattice spacings of i-carbon crystals. The
FFT of the HRTEM image of a single i-carbon crys-
tal (fig. 11E)showsthreevaluesrepresenting two
lattice planes, and the HRTEM image of the same
i-carbon crystal (fig. 11F) shows three values rep-
resenting two lattice planes, as viewed along the
[001] zone axis. The EDS, EELS, and EFTEM anal-
yses are not shown for these NDs but are similar
to the analyses above for NDs.
Twinning in YDB NDs. The YDB NDs larger than
2 nm are usually made up of two or more crystals
that share a common lattice plane (the twin plane)
and grow symmetrically in different orientations;
twinned NDs were observed at all YDB sites. Twin-
ning is also commonly observed in meteorites, cos-
mic-impact craters, and commercial NDs (Israde-
Alca´ntara et al. 2012band references therein).
Twins can form in numerous configurations, in-
cluding “star twins,” as observed by Tian et al.
(2011) in the YDB layer from Lommel. Figure 12A
shows a multiply twinned ND from Kangerlussuaq,
Greenland, composed of 120 individual crystals
with lattice plane spacings and angles character-
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 489
Figure 6. Transmission electron microscopy images (top) and selected-area electron diffraction patterns (bottom)
used to identify nanodiamonds (NDs) in carbon spherules (CS). A,B, i-Carbon from Kimbel Bay, North Carolina
(Younger Dryas Boundary [YDB]: 721 ppb at 351 cm below surface [cmbs]). C,D, n-Diamond from Topper, South
Carolina (YDB: 108 ppb at 60 cmbs). E,F, n-Diamond from Lingen, Germany (YDB: 431 ppb at 43.5 cmbs); note twin
ND at upper right. A color version of this figure is available online.
istic of n-diamond, as reported by Yang et al. (2008).
Figure 12Bis an FFT of the central crystal and dis-
plays eight lattice spacings that are consistent with
n-diamonds and cubic NDs. Figure 12Cis a “star-
twin” n-diamond, so named because of its fivefold
star-like symmetry. More twinned n-diamonds are
shown in figure C6.
TEM, SAD, and Scanning Electron Microscopy of NDs
in Carbon Spherules. Figure 13A, from Gainey,
Michigan, is a TEM image of a carbon spherule
fragment, showing embedded NDs as black dots
within the amorphous matrix at the arrow. The
EDS analyses indicate that these are carbon parti-
cles. Figure 13Bis a photomicrograph of a typical
YDB carbon spherule. Figure 13Cis an SAD pat-
tern, demonstrating that the particles are n-dia-
monds with a possible minor admixture of other
NDs. Figure 13Dis an HRTEM image from the
Chobot site of a carbon spherule fragment contain-
ing NDs, such as the dark object marked by the
arrow. This fragment was removed from inside a
carbon spherule with a needle, demonstrating that
some NDs form throughout the interior matrix of
the spherules. The photomicrograph (fig. 13E)
shows a carbon spherule with a hollow interior.
Figure 13Fis an SAD pattern demonstrating that
these particles are n-diamonds. The NDs found in
carbon spherules are indistinguishable from the
rounded NDs initially discovered by Ro¨ sler et al.
(2006) and reported in Yang et al. (2008).
We investigated whether NDs always are dis-
tributed throughout the interior matrix of carbon
spherules and glass-like carbon, the latter of which
has been reported to contain NDs (van Hoesel et
al. 2012). We used a focused ion beam to mill a
piece of glass-like carbon extracted from the YDB
layer at the M33 site, the rim of a Carolina bay in
Myrtle Beach, South Carolina (for site details, see
Firestone et al. 2007). The TEM analyses showed
that diamonds were present only from the surface
down to a depth of 0.75 mmandwerenotobserved
in the interior (fig. 14A). The surface layer was
sharply demarcated and fused to the interior of the
spherule. Figure 14Bshows a chip of the glass-like
carbon surface layer removed with a needle; it con-
tains hundreds of densely packed NDs. Similarly,
examination of carbon spherules from Watcombe
Bottom, United Kingdom, suggested that some
NDs were clustered in a thin layer on the outside
of carbon spherules (fig. 14C). On the other hand,
the carbon spherule fragment from the Chobot site
(fig. 13D) displays NDs from deep within a spher-
ule, and Ro¨sler et al. (2006) reported NDs attached
to the inner surfaces of vesicles in European carbon
spherules. These results indicate that at least some
NDs form only on surfaces of carbon spherules and
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490 C . R . K I N Z I E E T A L .
Figure 7. Scanning transmission electron microscopy (STEM) images (A,D), selected-area electron diffraction patterns
(B,E), and energy-dispersive X-ray spectrometry plots (C,F) for elemental abundance of carbon: Younger Dryas
Boundary nanodiamonds (NDs) from Lake Cuitzeo (493 ppb at 280 cm below surface; AC) and synthetic NDs from
PlasmaChem (DF). Carbon in both is greater than 98%. HAADF phigh-angle annular dark field. A color version
of this figure is available online.
Figure 8. Electron energy-loss spectroscopy spectra for differentiating cubic nanodiamonds (NDs) from n-diamonds,
i-carbon, and other forms of carbon. A, Younger Dryas Boundary (YDB) NDs from Murray Springs (426 ppb at 46.5
cm below surface). B, Synthetic cubic NDs. C, YDB n-diamonds from Murray Springs; solid lines represent spectra
for graphite, amorphous carbon, n-diamond, and i-carbon from Berger et al. (1988); the graphene spectrum is from
Daulton et al. (2010). A color version of this figure is available online.
glass-like carbon, whereas others form throughout
them. The reason for this difference is unclear, but
finding NDs on spherule surfaces is consistent with
one scenario, in which molten carbon spherules
and glass-like carbon in an impact fireball were ex-
posed briefly to anoxic conditions and high tem-
peratures that caused NDs to form on their surface
layers, but not inside them, while preventing the
carbon from incinerating.
Identification of Lonsdaleite-Like Crystals. Poten-
tial YDB lonsdaleite crystals have been identified
and analyzed with HRTEM, FFT, SAD, and EDS
(see Kennett et al. 2009b; Kurbatov et al. 2010;
Israde-Alca´ntara et al. 2012b). On the basis of EDS
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 491
Figure 9. Energy-filtered transmission electron microscopy (EFTEM) for identifying carbon bonding in particles. A,
Nanodiamonds (NDs) from Lake Cuitzeo (Younger Dryas Boundary: 493 ppb at 280 cm below surface) in a zero-loss
EFTEM image (reverse contrast for clarity). B, Jump ratio map, exhibiting NDs with sp
3
bonding in the lighter areas
(reverse contrast for clarity). N pn-diamond; I pi-carbon; C pcubic diamond; L plonsdaleite-like crystal; AC p
amorphous carbon grid film. A color version of this figure is available online.
and EELS measurements, all the lonsdaleite-like
crystals observed contain only carbon, with no
other elements present but oxygen, eliminating the
possibility that they are unidentified, noncarbon
mineral. We have observed the crystals along three
major zone axes ([0001], [ ], and [ ]), and all
¯¯
0111 1121
measured lattice planes are consistent with lons-
daleite and no other known carbon allotrope, in-
cluding graphite, graphene, and graphane. Never-
theless, these crystals are too rare to allow
definitive identification with all available analyti-
cal methods. Because many new, very hard forms
of carbon have been discovered within the past few
decades, these crystals may be some unidentified,
diamond-like carbon allotrope. Therefore, we con-
sider the identification of lonsdaleite to be provi-
sional, pending further work. We include the evi-
dence below for the benefit of other researchers.
Daulton (2012) questioned the identification of
lonsdaleite in Kennett et al. (2009b), and we agree
that the one cluster of nanoparticles in figure 2D
2Fof the latter paper appears to consist of graphene-
graphane aggregates, which mimic the d-spacings
of lonsdaleite. We thank Daulton (2012) for point-
ing this out. He also questioned figure 2A–2Cof
Kennett et al. (2009b). Although the analyses were
insufficient to conclusively identify the nanocrys-
tal shown as lonsdaleite, we find no evidence to
eliminate it as a possibility, as discussed below in
“Angular Lonsdaleite-Like Crystals.”
Nearly all lonsdaleite observed in known impact
craters is angular (Koeberl et al. 1997), and occa-
sionally, YDB lonsdaleite-like crystals have been
observed that are angular (Kennett et al. 2009b).
However, in most cases, YDB NDs are rounded to
subrounded in shape. The rounded lonsdaleite-like
crystals may be due to modification by the extrac-
tion process, but this seems unlikely because acid-
extracted n-diamonds are morphologically identi-
cal to nonacidized n-diamonds found in carbon
spherules. Alternately, the rounded shapes may re-
sult from a different mode of formation. For ex-
ample, subrounded to rounded commercial lons-
daleite has been produced by microplasma
dissociation of ethanol vapor (Kumar et al. 2013),
under conditions somewhat similar to those in an
impact event, i.e., anoxic atmosphere and a carbon
source. Below, we describe some analyses used to
characterize the lonsdaleite-like crystals.
Angular Lonsdaleite-Like Crystals. A single YDB
site, Arlington Canyon, California, contains flake-
like lonsdaleite-like crystals (Kennett et al. 2009b),
ashapesimilartothatofpreviouslyreportedcubic
NDs (Ro¨ sler et al. 2006) and plate-like lonsdaleite
from known impact craters (Koeberl et al. 1997). A
STEM image shows a tabular lonsdaleite-like crys-
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492 C . R . K I N Z I E E T A L .
Figure 10. Tilted transmission electron microscopy (TEM) images of a field of nanodiamonds. TEM images (A,B)
and selected-area electron diffraction (C) pattern of n-diamonds from Murray Springs (YDB: 426 ppb at 46.5 cm below
surface), tilted through 45#(!30#[A] through "15#[B]). Comparison of various selected objects, such as 1–4, dem-
onstrates that these particles are three-dimensional, rounded to subrounded crystals. A color version of this figure is
available online.
tal (2.9 mmlong)fromtheYDBatArlingtonCanyon
(fig. 15A). This is the same lonsdaleite-like grain
shown in Kennett et al. (2009b) as figures 2A–2C
and S2B, referred to above. Figure 15Bis a TEM
image of the same crystal as in panel A. Figure 15C
is an EDS elemental map of the same crystal and
shows the composition to be carbon (lighter con-
trast), with no other elements present.
Figure 16Ais an HRTEM image showing the
same crystal. The double lines define three sets of
lattice planes consistent with { }-type planes of
¯
1010
lonsdaleite (prism planes) with a d-spacing of 2.18
A
˚, as viewed along the [0001] zone axis. Figure 16B
presents an FFT of an HRTEM image of the same
crystal, displaying a spot pattern consistent with
the d-spacings for lonsdaleite shown in table D1.
The spot pattern matches crystallographic simu-
lations performed for lonsdaleite. Multiple mea-
surements with a calibrated beam (diamond stan-
dard) attained an accuracy of approximately "1%,
producing a range of 2.16–2.20 A
˚for the 2.18-A
˚
d-spacing. We also measured d-spacings for com-
mercial graphene and were able to easily distin-
guish between the d-spacings of 2.18 A
˚for the lons-
daleite-like crystal and 2.13 A
˚for graphene,
eliminating both graphene or graphane as candi-
dates. Although the lonsdaleite-like crystals may
be some other unknown carbon-based mineral,
there is no current evidence that excludes the pos-
sibility that it is lonsdaleite.
Rounded Lonsdaleite-Like Crystals. The YDB layer
at several sites also contains rounded lonsdaleite-
like crystals. Figure 17Ais a STEM image from the
Greenland Ice Sheet near Kangerlussuaq, exhibiting
rounded lonsdaleite-like crystals (arrows) mixed
with n-diamonds and i-carbon, all ranging from 4
to 200 nm in diameter. Figure 17Bis an HRTEM
image of a rounded 10-nm lonsdaleite-like crystal.
The EDS results were presented in Kurbatov et al.
(2010), confirming that the crystal is carbon, and
an EELS spectrum indicated high sp
3
bonding, elim-
inating the possibility that it is graphite, graphene,
or graphane. Figure 17Cis an FFT of an HRTEM
image of the same lonsdaleite-like crystal, showing
lattice spacings consistent with lonsdaleite.
We also extracted lonsdaleite-like crystals from
the YDB layer in several caves. Figure 18A, 18B
shows a 200-nm-long lonsdaleite-like crystal from
Sheriden Cave in Ohio. We tilted the TEM stage
to confirm that the crystal is three-dimensional and
rounded. Figure 18Cis a STEM image showing a
53-nm-wide object from Daisy Cave on San Miguel
Island, one of the Channel Islands located off Santa
Barbara, California. Using variable focusing and
tilting of the electron beam, we determined that
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 493
Figure 11. Selected-area electron diffraction (SAD), fast Fourier transform (FFT), and high-resolution transmission
electron microscopy (HRTEM) images. AC, SAD pattern (A) and FFT (B) of the HRTEM image (C) of an n-diamond
from Murray Springs (Younger Dryas Boundary [YDB]: 426 ppb at 46.5 cm below surface [cmbs]). DF, SAD pattern
(D) and FFT (E) of the HRTEM image (F) of i-carbon from Lake Cuitzeo (YDB: 493 ppb at 280 cmbs). Images Band
Care from Israde-Alca´ntara et al. (2012b) and are used with permission. A color version of this figure is available
online.
the object is a three-dimensional ball. The EDS
analysis indicates that the ball is composed almost
solely of carbon, while HRTEM confirms that the
matrix is amorphous and studded with a mix of
NDs, including one n-diamond star-twin (2.06 A
˚)
and one lonsdaleite-like crystal (2.18- and 1.93-A
˚
d-spacings). We compared that 2.18-A
˚spacing to
the similar 2.13-A
˚d-spacing for graphene and found
that we were able to distinguish them, making it
highly unlikely that any of these lonsdaleite-like
crystals are graphene. Other than lonsdaleite, no
other known carbon allotrope matches all the evi-
dence for these crystals.
Origin of YDB NDs
Multiple explanations have been proposed for the
origin of YDB NDs, as follows.
Potential Origin by Cosmic Flux. Cubic NDs are
present in meteorites and cosmic dust (Hanneman
et al. 1967; Grady et al. 1995; Huss and Lewis 1995),
and lonsdaleite is present in some meteorites
(Daulton et al. 1996). These observations led Pinter
et al. (2011) and others to speculate that YDB mi-
crospherules and NDs arrived as components of the
gradual, noncatastrophic rain of cosmic debris; if
that speculation were correct, those NDs should
display cosmic chemical signatures. Instead, anal-
yses indicate that the isotopic compositions of car-
bon and nitrogen (d
13
C, d
15
N, and C/N) in YDB NDs
are consistent with a terrestrial origin (Tian et al.
2011; Israde-Alca´ntara et al. 2012b). Those results
are supported by Gilmour et al. (1992), who found
that d
13
C and d
15
NvaluesforK-PgNDsareconsis-
tent with formation from terrestrial carbon during
the impact itself (Belcher et al. 2005).
Potential Origin from Volcanism or in the Mantle.
Cubic diamonds occur in terrestrial deposits, such
as kimberlite pipes, which originated from the
mantle. Boslough et al. (2012) pointed out that YDB
lonsdaleite may originate with terrestrial cubic di-
amonds because it has been found in a cubic dia-
mond deposit in North Kazakhstan, in Ukrainian
titanium placer deposits, in Yakutian diamond
placers, and in metamorphosed basaltic rocks on
the Kola Peninsula and in the Urals. However, it
is unclear whether all of those lonsdaleite examples
are terrestrial in origin. For example, Shelkov et al.
(1998) presented evidence that lonsdaleite in the
Yakutian placers eroded from an impact crater.
Daulton (2012) also suggested that YDB NDs
may be derived from mantle material, but isotopic
analyses (Tian et al. 2011) are inconsistent with a
mantle origin. If such distribution occurred, the
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494 C . R . K I N Z I E E T A L .
Figure 12. High-resolution transmission electron microscopy (HRTEM) and fast Fourier transform (FFT) images of
nanodiamonds (NDs) from Kangerlussuaq, Greenland (Younger Dryas Boundary: 174 ppb at 548 cm below surface).
A, HRTEM image of an unusually large, multiply twinned n-diamond or flawed cubic ND (53 nm #39 nm) with
20 conjoined crystals. Center diagram shows typical d-spacings (in A
˚) and corresponding angles. B, FFT of HRTEM
image of the central crystal in Ashows eight d-spacings that are consistent with n-diamond and cubic NDs, when
viewed along the [011] zone axis. C, HRTEM image of 24-nm-wide n-diamond “star-twin.” Arrows are at plane
boundaries. Parallel lines indicate d-spacing of 2.06 A
˚. A color version of this figure is available online.
geochemical signature of the mantle host material
should have been detected in more than 700 geo-
chemical analyses conducted on YDB materials
(Wittke et al. 2013), and instead, no such signature
is apparent. Mantle-derived NDs have never been
found in any known geological column associated
with coeval peaks in impact markers, arguing
against this hypothesis. In any event, terrestrial
lonsdaleite has never been observed in any deposits
of any age in Europe or North America, where YDB
lonsdaleite-like crystals are currently found.
We also considered whether NDs might be pro-
duced from volcanic eruptions. To test this, we ap-
plied our protocol (see “Material and Methods”) to
tephra from the Laacher See eruption that occurred
near the time of the YDB event. We observed no
NDs and no magnetic spherules, eliminating the
possibility that this eruption deposited those prox-
ies in the YDB layer.
Potential Origin in Wildfires. Ro¨sler et al. (2005,
2006) and Yang et al. (2008) reported ND-enriched
carbon spherules of unknown origin at 70 sites
across western Europe, including Germany, Aus-
tria, and Belgium. The ND-enriched carbon spher-
ules were found in upper soils, but recently, N.
Schryvers (2014, personal communication) was
more specific, indicating that their samples were
collected from between 10 and 20 cm deep, after
removal of topsoil. They wrote that the soils were
“modern” but reported no dates. Yang et al. (2008,
p. 941) stated that some ND-rich carbon spherules
in Germany were found associated with “small-
scale crater-like structures,” estimated to be 1000
yr old, but no craters were associated with the ND-
rich carbon spherules in other countries. They
added that their origin is unclear but that “an im-
pact related origin ... cannot be ruled out” (p. 941),
If so, the age is currently unknown, because near-
surface sediments can range in age from modern to
millions of years old. As an example, ND-enriched
carbon spherules from Gainey (14 cm deep) and
Chobot (33 cm deep) were intermixed with Clovis-
age tools dating from 13,250–12,800 cal BP (Waters
and Stafford 2007). Thus, it is conceivable that
some or all of the European near-surface, ND-rich
carbon spherules date to the YD onset. Determin-
ing the age of the surficial sediments at these sites
is necessary to answer these questions.
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 495
Figure 13. Transmission electron microscopy images (A,B,D,E) and selected-area electron diffraction patterns (C,
F) of carbon spherules from Gainey, Michigan (Younger Dryas Boundary [YDB]: 3933 ppb at 30 cm below surface
[cmbs]; AC), and Chobot, Alberta, Canada (YDB: 10 ppb at 13.5 cmbs; DF). A color version of this figure is available
online.
Van Hoesel et al. (2012, 2014) speculated about
apossiblewildreoriginfortheND-richEuropean
carbon spherules, on the basis of a recent discovery
by Su et al. (2011) that NDs form in candle flames.
The NDs are produced at high temperatures (1100#
1300#C) at the anoxic center of the flames, but be-
cause NDs combust at 400#–600#C in oxygen-rich
atmospheres (Hough et al. 1999), they are rapidly
destroyed as they approach the flame’s oxidation
boundary. To protect the NDs from destruction, Su
et al. (2011) developed an elaborate procedure using
porous aluminum foils to capture and extract the
NDs before they could combust. While innovative,
this elaborate process does not exist in nature. The
particles were identified as “face-centered cubic”
NDs, more commonly known as n-diamonds, and
there was no evidence of typical, body-centered cu-
bic NDs, as found in the YDB layer.
It is well established that carbon spherules can
be produced in intense wildfires involving conifers
(Firestone et al. 2007; Israde-Alca´ntaraetal.2012b).
However, no natural wildfires are known to pro-
duce NDs inside carbon spherules or other parti-
cles. Similarly, no laboratory experiments have
been able to produce NDs under conditions that
normally appear at Earth’s surface. If NDs could be
produced in natural fires, which typically recur ev-
ery 100–1000 yr in any given area, they should be
common and ubiquitous in sediments of all ages.
Instead, NDs in contiguous stratigraphic horizons
are nonexistent to rare (Tian et al. 2011; Bement et
al. 2014) and do not correlate with sedimentary lay-
ers with high charcoal abundance (Bement et al.
2014). These observations are confirmed by our
own work at 22 YDB sites. Similarly, NDs havenot
been found above or below the K-Pg impact layer
(Carlisle and Braman 1991; Gilmour et al. 1992;
Bunch et al. 2008), even though biomass burning
is accepted as having been broadly pervasive over
the K-Pg boundary interval (Wolbach 1990).
In summary, there is no evidence for and no
known process for production of NDs in natural
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496 C . R . K I N Z I E E T A L .
Figure 14. Transmission electron microscopy (TEM) images of nanodiamonds (NDs) in glass-like carbon (GLC) and
carbon spherules (CS). A, TEM image from M33 Bay, Myrtle Beach, South Carolina (40 cm below surface [cmbs]);
the sectioned GLC displays only amorphous carbon and no NDs (the dark crust is mounting material). B, TEM image
of a flake from the surface of the GLC in A; selected-area electron diffraction patterns reveal a high abundance of n-
diamonds. C, TEM image from Watcombe Bottom, United Kingdom (Younger Dryas Boundary: 130 ppb at 65 cmbs)
shows a thin zone of cubic NDs along one edge of a fragment of a carbon spherule. A color version of this figure is
available online.
wildfires. This argues against biomass burning as
the source of the assemblage of NDs in the YDB
or other sedimentary sequences.
Potential Origin within Sclerotia. Scott et al.
(2010) and Hardiman et al. (2012) stated that all
carbon spherules from Arlington Canyon and other
sites are simply either charred fecal pellets or fun-
gal sclerotia. To be viable, the sclerotial hypothesis
must account for the presence of millions of NDs
entrained within each carbon spherule (Kennett et
al. 2009a). There is no credible mechanism by
which fungi can create NDs in sclerotia, but we
considered whether NDs might have adhered to
preexisting sclerotia while colocated in YDB sedi-
ment. For comparison, the average sedimentary
abundance of NDs is 200 ppb, whereas the ND
concentrations in carbon spherules is 135% at three
sites, a difference of more than one million times.
There is no plausible process by which sclerotia
could extract NDs from surrounding sediment,
concentrate them a million times, and do so only
at one time during the past 13,000 yr. Thus, the
best explanation is that ND-rich carbon spherules
derive from conifers that were incinerated by the
impact event (Israde-Alca´ntara et al. 2012b).
Potential Origin from Lightning. We considered
whether diamonds might form during high-tem-
perature lightning strikes. To evaluate this, we ap-
plied the protocol to extract potential NDs from a
collection of fulgurites but observed not even one
ND. Furthermore, Wittke et al. (2013) studied rem-
anent magnetism in YDB impact spherules that are
closely associated with NDs. They found no evi-
dence for lightning strikes in YDB sediment, thus
arguing against this hypothesis.
Potential Origin as Anthropogenic NDs. Ro¨ sler et
al. (2006) and Bement et al. (2014) discovered NDs
in deposits near the ground surface. We investi-
gated the possibility that modern anthropogenic ac-
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 497
Figure 15. Younger Dryas Boundary lonsdaleite-like crystal. A, Scanning transmission electron microscopy image
from Arlington Canyon, California (1760 ppb at 462 cm below surface). B, Transmission electron microscopy images
of same crystal. C, Corresponding energy dispersive X-ray spectrometry elemental carbon map of the crystal; no other
elements were detected. Images from Kennett et al. (2009b); used with permission. A color version of this figure is
available online.
Figure 16. Younger Dryas Boundary (YDB) lonsdaleite-like crystal from Arlington Canyon (1760 ppb at 462 cm below
surface). A, High-resolution transmission electron microscopy of the crystal; B,correspondingfastFouriertransform.
A color version of this figure is available online.
tivities might produce synthetic NDs that migrated
downward to the YDB. We examined fly ash residue
from a modern New Jersey power plant that incin-
erates coal at high temperatures under anoxic con-
ditions, similar to some laboratory conditions that
produce NDs. We found abundant graphene but no
NDs and no melt-glass containing high-tempera-
ture, melted quartz. Furthermore, some YDB NDs
are found up to 5mbelowsurfacebutnotinin-
tervening layers, making it unlikely that they mi-
grated downward from the surface. In addition, we
found no detectable NDs in surficial sediments in-
vestigated at eight sites (fig. 2; table D4). All these
findings argue against the hypothesis that NDs are
produced through anthropogenic activities and are
common in surface and other sediments.
Potential Origin by Cosmic Impact. Cubic NDs
have been reported at the K-Pg boundary (Gilmour
et al. 1992; Hough et al. 1997), and Israde-Alca´ntara
et al. (2012b)reportedthatYDBNDsaremorpho-
logically and compositionally similar to those in
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498 C . R . K I N Z I E E T A L .
Figure 17. Scanning transmission electron microscopy (STEM) and high-resolution transmissionelectron microscopy
(HRTEM) images of lonsdaleite-like crystals. A, STEM image of group of lonsdaleite-like crystals (arrows) mixed with
other NDs, from Kangerlussuaq (Younger Dryas Boundary [YDB]: 174 ppb at 548 cm below surface [cmbs]). B, HRTEM
image of a 10-nm lonsdaleite-like monocrystal from Lake Cuitzeo (YDB: 493 ppb at 280 cmbs); one ( ) plane with
¯
1011
a spacing of 1.93 A
˚is visible, along with the ( ) plane at 2.18 A
˚, consistent with lonsdaleite. C, Fast Fourier
¯
1010
transform of an HRTEM image of the same crystal as in B, with d-spacings along the [ ] zone axis, revealing one
¯
0111
( ) plane with a lattice spacing of 2.18 A
˚and two ( ) planes with lattice spacings of 1.93 A
˚. A color version
¯¯
1010 1011
of this figure is available online.
the K-Pg (Kennett et al. 2009a, 2009b;Kurbatovet
al. 2010). Angular lonsdaleite crystals also formed
in some impact events via shock metamorphism of
graphite in the target rocks (Hough et al. 1997; Koe-
berl et al. 1997; Langenhorst et al. 1998; DeCarli
et al. 2002; Oleinik et al. 2003). Lonsdaleite grains
have been reported in impact events, e.g., Ries Cra-
ter, the K-Pg event (Bunch et al. 2008), and the 1908
Tunguska airburst in Siberia (Bunch et al. 2008;
Kvasnytsya et al. 2013). Although lonsdaleite is
known to be formed through shock metamorphism
during surface impacts, its presence at the site of
the Tunguska airburst indicates that it also can
form during cosmic airbursts. This is demonstrated
in laboratory experiments (Miura and Okamoto
1997), in which a high-velocity impact into a lime-
stone target produced carbon vapor that condensed
into graphite inside a high-temperature, reducing
vapor plume. Subsequently, lonsdaleite and cubic
NDs formed when the carbon plume reacted with
water ice, creating oxidizing conditions. This dem-
onstrates that lonsdaleite can form through a pro-
cess similar to carbon vapor deposition (CVD), es-
pecially if the YDB impactor struck the ice sheet
or oceans, as proposed by Firestone et al. (2007).
Criticism of an impact origin for the YDB has
included an apparent absence of an impact crater
(Boslough et al. 2012). However, this position con-
tradicts a broad consensus among impact research-
ers, including some of those coauthors, that some
impact events lack known craters or that the cra-
ters remain undiscovered (Boslough and Crawford
2008). Some examples are the Tunguska airburst
debris field (2#10
3
km
2
), the Libyan glass field
(2#10
3
km
2
), the Dakhleh glass field (1#10
3
km
2
), and the Australasian tektite field (5#10
7
km
2
, or 10% of the planet). This apparent lack of
cratering has been variously explained. Some im-
pacts were hypothesized to have been airbursts, or
alternately, some events formed craters that have
yet to be found (Boslough and Crawford 2008), as
may be the case with the YDB impact. Regardless,
these widely accepted, craterless impact events de-
posited up to millions of tons of spherules, melt-
glass, and NDs across up to 10% of Earth.
There are only two known layers, broadly dis-
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 499
Figure 18. Younger Dryas Boundary lonsdaleite-like crystals from two caves. A,B, Transmission electron microscopy
(A) and selected-area electron diffraction (B) images of 200-nm-long, three-dimensional, lonsdaleite-like crystal from
Sheriden Cave, Ohio (108 ppb at 45.3 cm below surface [cmbs]), as viewed along the [0001] zone axis. C,Scanning
transmission electron microscopy image of 53-nm, three-dimensional carbon spherule containing n-diamonds and
lonsdaleite-like crystals, from Daisy Cave, California (100 ppb at 80 cmbs). D,High-resolutiontransmission electron
microscopy (HRTEM) image of the nanodiamond marked “D” in C; arrows define common lattice planes. E, Fast
Fourier transform of an HRTEM image of another nanocrystal, marked “E” in C,showingd-spacingsconsistentwith
lonsdaleite when viewed along the [ ] zone axis, revealing one ( ) plane with a lattice spacing of 2.18 A
˚and
¯¯
0111 1010
two ( ) planes with lattice spacings of 1.93 A
˚. CS pcarbon spherule; Sed psediment. A color version of this
¯
1011
figure is available online.
tributed across several continents, that exhibit co-
eval abundance peaks in a comprehensive assem-
blage of cosmic-impact markers, including NDs,
high-temperature quenched spherules, high-tem-
perature melt-glass (1730#to 12200#C), carbon
spherules, iridium, and aciniform carbon. One of
those layers is at the K-Pg impact boundary, and
the other is at the YDB. Other events, such as the
Chesapeake Bay and Popigai craters, include a
nearly complete assemblage, but some markers are
missing, possibly because no one has searched for
them. This unique assemblage of proxies has never
been reported to result from meteoritic flux, wild-
fires, volcanism, or any other nonimpact process.
At present, a cosmic-impact event is the only
known mechanism capable of distributing NDs and
the complete assemblage of YDB proxies across
multiple continents.
How NDs Might Form in a Cosmic Impact. Hough
et al. (1997) suggested that the K-Pg NDs formed by
the CVD process, which requires a source of carbon
vapor and the reducing atmosphere of the fireball
(Wen et al. 2007). For the K-Pg, it is proposed that
the NDs formed when the impactor collided with
carbon-rich Yucatan bedrock, e.g., limestones and
dolostones containing hydrocarbons (Belcher et al.
2005). In a related discovery, hydrocarbons in some
oil fields adjacent to the crater in Yucatan contain
n-diamonds and are proposed to have formed during
the K-Pg impact event (Santiago et al. 2004).
Synthetic cubic NDs, n-diamonds, and i-carbon
are produced by many industrial or laboratory pro-
cesses, 14 of which are listed in table D5 (Wen et al.
2007). In addition to a source of carbon, the produc-
tion of these NDs requires the presence of at least
two of the following conditions: high temperatures,
high pressures, and low- to zero-oxygen (anoxic)
atmospheres. Regarding temperature, 11 of the 14
processes require high temperatures of up to 3400#C,
beyond the normal range observed in nature. Four
of the processes require high pressures of 14–70
GPa that are well beyond typical natural processes.
Four involve near-vacuum conditions unknown at
Earth’s surface, and nine require oxygen-free, reduc-
ing atmospheres (e.g., argon, hydrogen) that do not
support combustion, as required for wildfires. Ten
call for exotic processes, such as plasma jets, lasers,
microwave beams, catalysts, and/or strong magnetic
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500 C . R . K I N Z I E E T A L .
fields, that do not exist in nature. Furthermore,nine
of these processes yield only n-diamonds and i-car-
bon and not cubic NDs or lonsdaleite. Thus, in every
known case of industrial production, the requisite
conditions do not occur in nature but do occur dur-
ing a cosmic-impact event.
During our experiments investigating formation
mechanisms, we discovered that NDs are com-
monly present in commercially produced activated
carbon from both Norit and Calgon Carbon. Pro-
duced at 1000#C in a low-oxygen steam atmo-
sphere, the activated carbon containsn-diamonds
and i-carbon but no cubics or lonsdaleite. The feed-
stock used for production of NDs is charcoal that
is usually charred from wood at 500#C, and our
analyses indicate that the charcoal does not contain
any NDs before or after charring. Later, during an
activation process that uses superheated steam
(1000#C), the NDs grow within the activated car-
bon at abundances similar to those found in YDB
carbon spherules (fig. C7). In multiple experiments
duplicating the commercial process, we demon-
strated that formation of these NDs requires exotic
atmospheres (steam, argon, or CO
2
)combinedwith
temperatures of 1000#–1200#C, similar to other in-
dustrial processes that yield NDs (table D5). The
conditions required to produce NDs in activated
carbon mimic those in a cosmic impact, e.g., anoxia
and high temperatures.
Regarding the formation of lonsdaleite, industrial
diamond research has been underway for nearly 50
yr, since lonsdaleite was first synthesized with ex-
plosives in 1966 by one of us (DeCarli 1966). The
process is similar to shock-formation conditions in
acosmic-impactevent,duringwhichlonsdaleite
typically forms from the high-pressure transfor-
mation of graphite. However, synthetic lonsdaleite
can also be produced under nonshock conditions,
e.g., by growth in a hydrogen plasma jet in a CVD-
like process (Maruyama et al. 1992) and by en-
hancement of carbon in silicon carbide wafers (Go-
gotsi et al. 2001; Welz et al. 2006; table D5). These
other processes suggest that lonsdaleite could form
without physical shock at high temperatures in the
fireball of a cosmic-impact event. If so, the lons-
daleite-like crystals that we have observed may
have formed that way.
The CVD-like production of NDs is proposed to
occur in extrasolar material (Daulton et al. 1996),
most likely during the explosion of a carbon-rich
star. Several studies have speculated that YDB NDs
may have formed through CVD (Tian et al. 2011;
van Hoesel et al. 2012, 2014), although they offered
no evidence as to whether such a process could occur
independently of an impact. The plausibility of an
impact-related source for the YDB NDs is supported
by the fact that requisite conditions for ND for-
mation by CVD in the laboratory and space (a carbon
source and anoxia) also occur in an impact fireball.
In a related discovery in the YDB layer in Bel-
gium, Tian et al. (2011) found “carbon onions,”
which are nanosized objects formed from concen-
tric shells of carbon. They noted that NDs can form
within carbon onions under anoxic conditions in
the laboratory and speculated that the carbon on-
ions might serve as nanometer-sized pressure cells
for YDB ND formation. Later, van Hoesel et al.
(2012) remarked that cubic diamonds form along-
side carbon onions in wood experimentally charred
at 700#Candcooledinananoxic(nitrogen)atmo-
sphere. However, those conditions are unlike those
in wildfires or other terrestrial processes but are
similar to the ones in an impact/airburst. Israde-
Alca´ntara et al. (2012b)alsoreportedcarbononions,
some apparently containing nanocrystals, and pro-
posed that the requisite conditions could occur dur-
ing an impact. One possible mechanism is that the
thermal radiation from the air shock at 20,000#C
could flash-pyrolyse vegetation to provide available
elemental carbon, after which reactions with the
atmosphere would locally deplete the oxygen, per-
mitting formation of NDs from carbon vapor.
Future Work. It is important to continue inves-
tigating the origin of YDB NDs, especially of lons-
daleite-like crystals, because lonsdaleite has been
considered an important proxy for cosmic impact.
It would also be useful to use Raman spectroscopy
for more thorough characterization of YDB NDs,
although this would require the extraction of a far
larger quantity of NDs (approx. 110 mg of each sam-
ple). Adequate quantities are more readily available
from the margin of the Greenland Ice Sheet, where
large amounts of ice can be extracted from the ex-
posed YDB layer (Kurbatov et al. 2010).
Conclusions
We have presented a detailed protocol for isolating
YDB NDs, requiring the use of numerous reagents.
The identification of the isolated NDs involves two
main methods, electron microscopy imaging and
electron spectroscopy, using up to nine imaging,
analytical, or quantification procedures: scanning
electron microscopy, STEM, TEM, HRTEM, EDS,
SAD, FFT, EELS, and EFTEM. The entire procedure
is labor-intensive and technically demanding. Even
so, it has proven to be effective and replicable by
skilled independent groups, based on the processing
of more than 100 samples. The presence of NDs at
24 sites in 10 countries on three continents, in-
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Journal of Geology N A N O D I A M O N D - R I C H L AY E R 501
cluding results from six independent groups, is
strong evidence for the existence of YDB abundance
peaks in NDs.
Analysis of YDB dates indicates that 18 of 24
sites, including the Aalsterhut and Arlington
Canyon sites, are statistically part of the same pop-
ulation, with ages falling within the proposed YDB
age range of 12,800 "150 (12,950–12,650) cal BP.
These ages also correspond to the onset of YD cli-
mate change in the GISP2 ice core within an age
range of 12,892 "260 (13,152–12,632) b2k, con-
sistent with the hypothesis that the cosmic impact
triggered that cooling event. The YDB layer has
been found on each of the four continents currently
investigated.
Some researchers have proposed that YDB NDs
originated from wildfires, volcanism, the mantle,
and/or by unknown processes that are coinciden-
tally coeval, but those hypotheses can be rejected
because each fails to account for the entire assem-
blage of proxies. Numerous accepted impact events
display the same evidence as found at the YDB, and
the YDB and the K-Pg impact layers contain the
only known multicontinental, coeval abundance
peaks in the entire assemblage of proxies within
the past 65 m.yr. Of all the proposed hypotheses,
a cosmic-impact event at the onset of the YD cool-
ing episode is the only hypothesis capable of ex-
plaining the simultaneous deposition of peak abun-
dances in NDs, magnetic and glassy spherules,
melt-glass, platinum, and/or other proxies across at
least four continents (50 million km
2
). The evi-
dence strongly supports a major cosmic-impact
event at 12,800 "150 cal BP.
Author Affiliations
1. Department of Chemistry, DePaul University,
Chicago, Illinois 60614, USA; 2. Department of En-
vironmental Health Sciences/UCLA Center for Oc-
cupational and Environmental Health, University
of California, Los Angeles, California 90095, USA;
3. National Institute for Materials Science, Tsu-
kuba 305-0047, Japan; 4. Center for Advanced Ma-
terials Characterization at Oregon, University of
Oregon, Eugene, Oregon 97403, USA; 5. Depart-
ment of Anthropology, Pennsylvania State Univer-
sity, University Park, Pennsylvania 16802, USA;
6. SRI International, Menlo Park, California 94025,
USA; 7. Geology Program, School of Earth Science
and Environmental Sustainability, Northern Ari-
zona University, Flagstaff, Arizona 86011, USA;
8. Departamento de Geologı´a y Mineralogı´a, Edi-
ficio U-4, Instituto de Ciencias de la Tierra, Univ-
ersidad Michoacana de San Nicola´sdeHidalgo,C.P.
58060, Morelia, Michoaca´n, Mexico; 9. US Geo-
logical Survey, Menlo Park, California 94025, USA;
10. South Carolina Institute of Archaeology and
Anthropology, University of South Carolina, Co-
lumbia, South Carolina 29208, USA; 11. Depart-
ments of Anthropology and Geology, University of
Cincinnati, Cincinnati, Ohio 45221, USA; 12. Kim-
star Research, Fayetteville, North Carolina 28312,
USA; 13. Museum of Natural and Cultural History,
University of Oregon, Eugene, Oregon 97403, USA;
14. AMS
14
CDatingCentre,DepartmentofPhysics
and Astronomy, University of Aarhus, Ny Mun-
kegade 120, Aarhus, Denmark; and Centre for
GeoGenetics, Natural History Museum of Den-
mark, Geological Museum, Oester Voldgade 5-7,
DK-1350 Copenhagen, Denmark; 15. Exploration
Geologist, 1016 NN, Amsterdam, The Nether-
lands; 16. College of Liberal Arts, Rochester Insti-
tute of Technology, Rochester, New York 14623,
USA; 17. Lawrence Berkeley National Laboratory,
Berkeley, California 94720, USA; 18. Departament
de Prehisto` ria i Arqueologia, Universitat de Val-
e`ncia, Avenida Blasco Iba´n˜ ez 28, E-46010 Valencia,
Spain; 19. Departamento de Prehistoria y Arqueo-
logı´a, Facultad de Geografı´a e Historia,Universidad
Nacional de Educacio´naDistancia,PaseoSendadel
Rey 7, E-28040 Madrid, Spain; 20. GeoScience Con-
sulting, Dewey, Arizona 86327, USA; 21. Depart-
ment of Earth Science and Marine Science Insti-
tute, University of California, Santa Barbara,
California 93106, USA.
ACKNOWLEDGMENTS
We thank Nick Schryvers, of the University of Ant-
werp, and several anonymous reviewers for de-
tailed, helpful comments and corrections that led
to significant improvements in this contribution.
For samples and sampling assistance, we thank
James Steele (Watcombe), James Teller (Lake Hind),
William Topping (Gainey), and Malcolm LeCompte
and Mark Demitroff (Melrose and Newtonville).
HRTEM work was conducted at the Center for Ad-
vanced Materials Characterization at Oregon
(CAMCOR), located at the University of Oregon,
with support from the Office of Research. ICP-MS
determinations for elements were made possible by
NIEHS 1S10 RR017770. This research was sup-
ported, in part, for R. B. Firestone by US Depart-
ment of Energy contract DE-AC02–05CH11231 and
US National Science Foundation grant 9986999 and
for J. P. Kennett by US National Science Foundation
grants ATM-0713769 and OCE-0825322, Marine
Geology and Geophysics.
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502 C . R . K I N Z I E E T A L .
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... Nanodiamonds and diamond-like carbon have been used as indicators of cosmic impacts, including at the Cretaceous-Paleogene boundary (K-Pg) at ~ 65 Ma 29,30 and the Younger Dryas boundary (YDB) at 12.8 ka 31 . Kinzie et al. 31 concluded that impact-related nanodiamonds and diamond-like carbon (DLC or diamonoids) are produced from the pyrolysis of carbon sources, e.g., vegetation and carbonate rocks that were pyrolyzed during high-temperature, high-pressure airburst/impact events. To search for nanodiamonds in TeH sediment, we followed the protocol of Kinzie et al. 31 , who used multiple reagents to remove all minerals except refractory, acid-resistant carbon. ...
... Kinzie et al. 31 concluded that impact-related nanodiamonds and diamond-like carbon (DLC or diamonoids) are produced from the pyrolysis of carbon sources, e.g., vegetation and carbonate rocks that were pyrolyzed during high-temperature, high-pressure airburst/impact events. To search for nanodiamonds in TeH sediment, we followed the protocol of Kinzie et al. 31 , who used multiple reagents to remove all minerals except refractory, acid-resistant carbon. www.nature.com/scientificreports/ ...
... Analyses by transmission electron microscopy (TEM) and selected-area electron diffraction (SAD) indicate that the structures are composed of quasi-amorphous carbon that does not produce SAD patterns (Fig. 8c), even though organized, short-range structures are present (Fig. 8b). This material is commonly referred to as diamonoid or diamond-like carbon (DLC) 31 , representing the smallest unit observed in a diamond crystal lattice. These structures are nearly as hard as diamond and are stable at temperatures up to ~ 1000-1200 °C 31 . ...
Article
Full-text available
We present evidence that in ~ 1650 BCE (~ 3600 years ago), a cosmic airburst destroyed Tall el-Hammam, a Middle-Bronze-Age city in the southern Jordan Valley northeast of the Dead Sea. The proposed airburst was larger than the 1908 explosion over Tunguska, Russia, where a ~ 50-m-wide bolide detonated with ~ 1000× more energy than the Hiroshima atomic bomb. A city-wide ~ 1.5-m-thick carbon-and-ash-rich destruction layer contains peak concentrations of shocked quartz (~ 5–10 GPa); melted pottery and mudbricks; diamond-like carbon; soot; Fe- and Si-rich spherules; CaCO3 spherules from melted plaster; and melted platinum, iridium, nickel, gold, silver, zircon, chromite, and quartz. Heating experiments indicate temperatures exceeded 2000 °C. Amid city-side devastation, the airburst demolished 12+ m of the 4-to-5-story palace complex and the massive 4-m-thick mudbrick rampart, while causing extreme disarticulation and skeletal fragmentation in nearby humans. An airburst-related influx of salt (~ 4 wt.%) produced hypersalinity, inhibited agriculture, and caused a ~ 300–600-year-long abandonment of ~ 120 regional settlements within a > 25-km radius. Tall el-Hammam may be the second oldest city/town destroyed by a cosmic airburst/impact, after Abu Hureyra, Syria, and possibly the earliest site with an oral tradition that was written down (Genesis). Tunguska-scale airbursts can devastate entire cities/regions and thus, pose a severe modern-day hazard.
... Until recently graphite, diamond and amorphous carbon were considered to be the only three carbon modifications of a terrestrial origin present in nature. Recently numerous publications [1][2][3][4][5][6][7] indicated the existence of two other uncommon metastable carbon allotropesface-centred cubic carbon (fcc carbon) and i-carbonon Earth. Nanoparticles of these carbon allotropes were found in carbon spherules of samples taken from soils and rocks in different countries of Europe and North America [1][2][3][4][5], crude oil [6], ice sheets from Greenland [7], etc. ...
... Recently numerous publications [1][2][3][4][5][6][7] indicated the existence of two other uncommon metastable carbon allotropesface-centred cubic carbon (fcc carbon) and i-carbonon Earth. Nanoparticles of these carbon allotropes were found in carbon spherules of samples taken from soils and rocks in different countries of Europe and North America [1][2][3][4][5], crude oil [6], ice sheets from Greenland [7], etc. In many cases, besides these carbon allotropes diamond nanoparticles were also found in the samples of soils and rocks from different countries [1][2][3][4][5]. ...
... Nanoparticles of these carbon allotropes were found in carbon spherules of samples taken from soils and rocks in different countries of Europe and North America [1][2][3][4][5], crude oil [6], ice sheets from Greenland [7], etc. In many cases, besides these carbon allotropes diamond nanoparticles were also found in the samples of soils and rocks from different countries [1][2][3][4][5]. Nevertheless, despite special features of electron diffractions patterns obtained from the nanoparticles of fcc carbon and i-carbon, in all the publications mentioned above they were regarded as polytypes of diamond. ...
Article
Until recently graphite, diamond and amorphous carbon were considered to be the only three carbon modifications of a terrestrial origin present in nature. Recently numerous publications indicated the existence of two other uncommon metastable carbon allotropes - face-centred cubic carbon and i-carbon – on Earth. Nanoparticles of these carbon allotropes were found in carbon spherules of samples taken from soils and rocks in different countries of Europe and North America, crude oil, ice sheets from Greenland, etc. The existence of these metastable carbon allotropes in nature appeared to confirm the Younger Dryas extraterrestrial impact hypothesis proposing such an impact over North America, that caused a global catastrophe and climate change. This hypothesis suggests an extraterrestrial impact origin of these carbon allotropes due to dynamic shock compression, since to date they have only been simultaneously produced in ultra-high pressures dynamic shock experiments. We report the first synthesis of nanocrystals of the both metastable carbon allotropes along with diamond at elevated temperatures and static ultra-high pressures. This provides evidence that nanocrystals of face-centred cubic carbon and i-carbon present in nature are likely to form in Earth's mantle, so that they have a terrestrial origin. Results of electron diffraction and high-resolution transmission electron microscopy clearly indicate that face-centred cubic carbon and i-carbon are characterized by unique crystal lattices, which have nothing common with the diamond crystal lattice. These two carbon allotropes are thought to be characterized by unconventional chemical bonds due to unusual combinations of their crystal lattice types and lattice parameters. The nature of chemical bonds in face-centred cubic carbon and i-carbon is supposed to be different from that of conventional basic chemical bonds (covalent, ionic and metallic bonding as well as the van der Waals forces). These carbon allotropes can therefore possess unique and potentially valuable properties suitable for different applications.
... As shown in Figure 7, Kinzie et al. 69 extended these findings by reporting the presence of nanodiamond peaks "in 22 dated stratigraphic sections in 10 countries of the Northern Hemisphere." The types observed included "cubic diamonds, lonsdaleite-like crystals, and diamond-like carbon nanoparticles, called n-diamond and i-carbon." ...
... Sun et al. 53 conducted a later study of osmium at the Debra L. Friedkin archeological site in Texas. They began by writing that "Reproducibility of these [impact] markers is challenged by failed duplication of proxy signatures at the same sites," citing Surovell et al.; 37 61 Wittke et al., 54 and Kinzie et al. 69 which collectively had replicated the microspherule and nanodiamond evidence. Sun et al. 53 reported that "The new results here thus independently confirm that the [PGE] abundances in the unradiogenic Os layers are likely a fingerprint of volcanic gas aerosols derived from large Plinian eruptions and not extra-terrestrial materials. ...
Article
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The progress of science has sometimes been unjustifiably delayed by the premature rejection of a hypothesis for which substantial evidence existed and which later achieved consensus. Continental drift, meteorite impact cratering, and anthropogenic global warming are examples from the first half of the twentieth century. This article presents evidence that the Younger Dryas Impact Hypothesis (YDIH) is a twenty-first century case. The hypothesis proposes that the airburst or impact of a comet ∼12,850 years ago caused the ensuing ∼1200-year-long Younger Dryas (YD) cool period and contributed to the extinction of the Pleistocene megafauna in the Western Hemisphere and the disappearance of the Clovis Paleo-Indian culture. Soon after publication, a few scientists reported that they were unable to replicate the critical evidence and the scientific community at large came to reject the hypothesis. By today, however, many independent studies have reproduced that evidence at dozens of YD sites. This article examines why scientists so readily accepted the early false claims of irreproducibility and what lessons the premature rejection of the YDIH holds for science.
... However, Firestone persisted and, at the American Geophysical Union meeting in May 2007, he and his new collaborators announced evidence of a bolide impact in North America at 12,900 cal BP. Their presentation was followed by a flurry of articles and papers (e.g., Firestone et al. 2007aFirestone et al. , 2007bFirestone et al. , 2008Kennett et al. 2008aKennett et al. , 2008bKennett et al. , 2009Kennett et al. , 2015Kinzie et al. 2014;Wittke et al. 2013;Kletetschka et al. 2018;Moore et al. 2017Moore et al. , 2019. The putative impact evidence was disputed in a slew of anti-impact papers (Pinter and Ishman 2008;Paquay et al. 2009;Surovell et al. 2009;Fiedel 2010;Holliday and Meltzer 2010;Pinter et al. 2011b;Boslough et al. 2012;Pigati et al. 2012;van Hoesel et al. 2012van Hoesel et al. , 2014Holliday et al. 2014;Scott et al. 2016;Daulton et al. 2017;Roperch et al. 2017;Holliday et al. 2020;Jorgeson et al. 2020;Sun et al. 2020). ...
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Americas Redefining the Age of Clovis: Implications for the Peopling of the This copy is for your personal, non-commercial use only. clicking here. colleagues, clients, or customers by , you can order high-quality copies for your If you wish to distribute this article to others here. following the guidelines can be obtained by Permission to republish or repurpose articles or portions of articles): July 7, 2014 www.sciencemag.org (this information is current as of The following resources related to this article are available online at
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journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t Diamond–lonsdaleite–graphite micro-samples collected from peat after the 1908 catastrophic blast in the Tunguska area were studied with scanning (SEM) and transmission electron (TEM) microscopy, NanoSecondary Ion Mass Spectrometry (NanoSIMS) and Х-ray synchrotron technique. The high-pressure carbon allotropes in the Tunguska samples are being described for the first time and contain inclusions of FeS (troilite), Fe–Ni (taenite), γ-Fe and (FeNi) 3 P (schreibersite). The samples are nodule-like in shape and consist of 99.5% carbon minerals, e.g. diamond4 lonsdaleite 4graphite. Micro-and nanoinclusions of troilite (up to 0.5 vol%), taenite, γ-iron and schreibersite fill cracks, cleavages and pores in the carbon matrix. Carbon isotope studies from the two analyses of the Tunguska foil showed δ 13
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The co-occurrence of a sharp dust peak, low lake levels, forest -reduction, and ice retreat at ca. 4-kyr BP throughout tropical Africa and West Asia have been widely explained as the effect of an abrupt climate change. The detailed study of soils and archaeological records provided evidence to re-interpret the 4 kyr BP dust event linked rather to the fallback of an impact-ejecta, but not climate change. Here we aim to further investigate the exceptional perturbation of the soil-landscapes widely initiated by the 4 kyr BP dust event. Results are based on soil data from the eastern Khabur basin (North-East Syria), the Vera Basin (Spain), and the lower Moche Valley (West Peru) compared with a new study at the reference site of Ebeon (West France). The quality of the 4 kyr BP dust signal and the related environmental records are investigated through a micromorphological study of pedo-sedimentary micro-fabrics combined with SEM-microprobe, mineralogical, and geochemical analyses. In the four regions studied, the intact 4 kyr BP signal is identified as a -discontinuous burnt soil surface with an exotic dust assemblage assigned to the distal fallout of an impact-ejecta. Its unusual two-fold micro-facies is -interpreted as (1) flash heating due to pulverization of the hot ejecta cloud at the soil surface, and (2) high energy deflation caused by the impact-related air blast. Disruption of the soil surface is shown to have been rapidly followed by a major de-stabilisation of the soil cover. Local factors and regional settings have exerted a major control on the timing, duration, and magnitude of landscape disturbances. Studies showed how a high quality signal allows to discriminate the short-term severe landscape disturbances linked to the exceptional 4 kyr BP dust event from more gradual environmental changes triggered by climate shift at the same time.
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Abstract— Nineteen diamond aggregate specimens (1–2 mm in size) from impactites of Popigai crater and five diamond samples (5–7 mm in size) from Ebeliakh river placers were studied. Our investigations indicate that samples from Ebeliakh were formed in an impact event with the exception of one specimen (Y7). The carbon isotopic composition of diamonds from Popigai varies within the previously reported limits (δ13C, −8 to −22%); whereas, diamonds from Ebeliakh placers show heavier values of δ13C (−7 to −10%). All the specimens studied contain very low amounts of N, mostly <20 ppm, but a few contained up to 60 ppm. For specimens, where the quantity of N allowed reliable analysis, δ15N values were found to be in the range of −3.9 to +11.9%. On the basis of combined Ar and N study, it was concluded that impact diamonds studied here can be a mixture of at least two types of gas carriers (e.g., different diamond components). A possible explanation would be involvement of a carbon vapour deposition (CVD) process or diamond growth in the impact melt in addition to the direct graphite-diamond shock transformation. The δ13C distributions and different N/36Ar correlations have indicated a difference between impact diamonds from Ebeliakh and diamonds extracted from Popigai crater. This could be explained by the existence of different diamond populations formed during the Popigai impact event. On the other hand, Ebeliakh diamonds could have resulted from a separate impact event to Popigai and an alternative crater is yet to be found.
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Combined high-resolution transmission electron microscopy, selected area electron diffraction and parallel electron energy loss spectroscopy are used to characterise carbon nano-phases found embedded in fused quartz. These appear after implantation of 1 MeV carbon ions, followed by annealing in argon, oxygen and forming gas for 1 hour at 1100°C. For Ar, virtually all of the carbon diffuses out of the substrate with no observable carbon clusters for all doses studied. After annealing in oxygen, a crystalline CO x phase is identified at the end of range, following a dose of 5×10 ¹⁷ C/cm ² . Three nano-crystalline carbon phases, including diamond, appear after annealing in forming gas: these form a layer 170 nm beneath the fused quartz surface for all ion doses. The average size of these clusters and the corresponding phases depend on the ion dose; the smallest size of 5–7 nm diameter crystallise as fcc [Formula: see text] diamond following a dose of 0.5× 10 ¹⁷ C/cm ² , whereas clusters of 8–13 nm diameter, for a higher dose of 2× 10 ¹⁷ C/cm ² , have a [Formula: see text] modified phase of diamond known as n-diamond. The largest clusters, diameter 15–40 nm, for a dose of 5× 10 ¹⁷ C/cm ² , have the cubic P2 1 3 (or P4 2 32) structure known as i-carbon. These buried layered diamond and diamond-related materials may have applications for field emission and optical waveguide type devices.