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Springer Earth System Sciences
Mirian M. Collantes
Laura Perucca
Adriana Niz
Jorge Rabassa Editors
Advances in
Geomorphology
and Quaternary
Studies in Argentina
Special Symposium from the Argentine
Association of Geomorphology and
Quaternary Studies, October 2017
Springer Earth System Sciences
Series Editors
Philippe Blondel, School of Physics, Claverton Down, University of Bath,
Bath, UK
Jorge Rabassa, Laboratorio de Geomorfología y Cuaternario, CADIC-CONICET,
Ushuaia, Tierra del Fuego, Argentina
Clive Horwood, White House, Praxis Publishing, Chichester, West Sussex, UK
The Springer Earth System Sciences series focuses on interdisciplinary research
linking the lithosphere (geosphere), atmosphere, biosphere, cryosphere, and
hydrosphere that build the system earth. The series seeks to publish a broad
portfolio of scientific books, aiming at researchers, students, and everyone
interested in this extremely interdisciplinary field. It covers the entire research
area of earth system sciences including, but not limited to, Earth System Modeling,
Glaciology, Climatology, and Human-Environment/Earth interactions. Springer
Earth System Sciences includes peer-reviewed monographs, edited volumes,
textbooks, and conference proceedings.
More information about this series at http://www.springer.com/series/10178
Mirian M. Collantes •Laura Perucca •
Adriana Niz •Jorge Rabassa
Editors
Advances in Geomorphology
and Quaternary Studies
in Argentina
Special Symposium from the Argentine
Association of Geomorphology
and Quaternary Studies, October 2017
123
Editors
Mirian M. Collantes
Instituto de Geociencias y Medio Ambiente
National University of Tucumán
Tucumán, Argentina
Laura Perucca
Instituto de Geología, CIGEOBIO
National University of San Juan
San Juan, Argentina
Adriana Niz
Departamento de Geología
National University of Catamarca
San Fernando del Valle de Catamarca,
Catamarca, Argentina
Jorge Rabassa
Laboratorio de Geomorfologia y Cuaternario
CADIC-CONICET
Ushuaia, Tierra del Fuego, Argentina
ISSN 2197-9596 ISSN 2197-960X (electronic)
Springer Earth System Sciences
ISBN 978-3-030-22620-6 ISBN 978-3-030-22621-3 (eBook)
https://doi.org/10.1007/978-3-030-22621-3
©Springer Nature Switzerland AG 2020
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Preface
Most of the papers that are included in this volume were presented during a special
Symposium on Geomorphology, Quaternary and Climatic Change studies, within
the framework of the 20th Argentine Geological Congress, that took place in 2017
in the province of Tucumán, northern Argentina.
This Symposium had as a main objective to offer a discussion space, about the
climatic and/or anthropogenic mechanisms that generate geomorphological pro-
cesses, from a space–time perspective and from an integrated and multidisciplinary
viewpoint. The characteristics of such processes in different regions of Argentina
were discussed, both in relationship to present climatic and hydrological variability,
as well as from palaeoclimatic studies, as an expression of past environmental
conditions. Several aspects related to the landscape genesis and evolution were
taken into consideration, attending to the different morphogenetic and morphocli-
matic environments. The scientific approach on the effects of climatic variability,
both seasonal, annual or pluriannual, was taken into account, as well as the impact
of global climatic change on the surface dynamics and the anthropogenic activity.
Besides, the integration of the palaeoclimatic and neotectonic influence on the
reconstruction of the present landscape evolution was considered, by means of
papers related to the study and analysis of the crustal deformation during the
Quaternary and the evidence of palaeoseismicity in the sedimentary record, oriented
to unveil the potentiality of an area as a potential seismogenic source. Diverse
contributions were presented focused on a neotectonic evaluation which would
allow a better knowledge of the Quaternary activity of the regional faults, their
co-seismic displacement, the fault slip rate, the earthquake magnitude and recur-
rence interval, the seismotectonic association of the historical earthquakes and the
morphological evolution of the landscape due to tectonics.
Thus, this volume gets together important scientific contributions, and it
becomes an appropriate ambient to communicate and discuss the advances of those
investigations devoted to the Quaternary palaeoclimatic and palaeoenvironmental
reconstruction and evolution and the basic and applied geomorphology of
Argentina. This volume also displays the complex framework of the Argentine
v
landscapes, as exposed by contributions from different regions of this country,
which extends from tropical to sub-Antarctic environments.
This volume starts with a challenging contribution of Rosa Compagnucci et al.
on the “Relationships among a supernova, a transition of polarity of the geo-
magnetic field and the Plio-Pleistocene boundary”, which considers that there is
an increase of Galactic Cosmic Rays (GCR) in space due to the birth of a supernova
near our solar system. This event would have started around 2.8 to 2.6 Ma and
finished between 1.7 and 1.5 Ma with a peak around 2.2 Ma; a consequent increase
of radiation input to Earth occurred. This increase was favoured by the weakening
and even suspension of the Earth’s magnetic field during the reversion between the
Gauss and Matuyama Chrons. All these factors together generated a relative
maximum of the GCR flux on the Earth, which could act as trigger of the beginning
of the first Quaternary glaciation and the appearance of the oscillations between
warmer and colder stages that characterized the Pleistocene.
The following contribution is by SC Grill et al., “Neogene continental deposits
of Bahía Blanca, Argentina. Palaeoenvironmental and palaeoclimatics infer-
ences”, which involves deposits of continental Neogene that outcrop in the Bahía
Blanca region, Argentina. The studies that were carried out in order to contribute to
the palaeoenvironmental and chronostratigraphical knowledge, involve sedimen-
tological, palaeomagnetic and magnetic susceptibility analyses. One of the outcrops
studied (Cueva de Los Leones) is mainly constituted of facies of fine to thick
sandstones, largely pedogenized and with important amounts of calcrete, whereas
the other (Loma Sarmiento) has a predominance of loess-like silt facies, reddish
brown in colour, an abundance of rhizoconcretions and evidence of pedogenic
processes. Both outcrops culminate in an important layer of calcrete of regional
scope, with particular morphologies at each of the sites. The palaeomagnetic
analysis leads to the conclusion that the sedimentation of the deposits underlying
the calcareous crust at the two sites was not synchronous. Reverse polarity was
recorded in the Cueva de Los Leones in contrast to Loma Sarmiento, where normal
polarity is predominant.
“Perched dunes in the Fuegian steppe, southern Argentina: archaeological
reservoirs of Holocene information”is the title of the contribution by
A. Coronato et al., comprising the description of the genesis and the geomorpho-
logical characteristics of three perched dune fields, located in shallow lakes named
as O´Connor, Amalia and Arturo. Perched dunes develop over the cliffs of most
of the ephemeral shallow lakes of the Fuegian steppe (lat. 53° S). They are formed
by the alternation of massive aeolian deposits and soils, which are distinguished
from each other by depth, colour, edaphic structures and organic matter content.
The edaphized levels are interpreted as palaeosoils formed during wetter periods
when the aeolian sedimentation was less intense. A set of radiocarbon dating,
obtained from organic matter in most of them and in different dunes, shows that
they were formed since the Late Glacial to the Late Holocene. This fact is con-
sidered as evidence of humid–arid periods cyclicity in the region.
vi Preface
“Morphotectonic and gravimetric analysis of the La Burra valley, central
Precordillera, San Juan, Argentina”is the contribution by LP Perucca et al. This
work describes new evidence of Quaternary tectonic activity in the La Burra
intermountain valley in the central Precordillera, San Juan Province, Argentina.
Quaternary structures are located in the eastern piedmont of the Sierra de la
Crucecita, and western piedmont of the Sierra de Talacasto (30º54’–31ºS and 68º
47’–68º55’W), about 70 km north-west of San Juan. By means of morphotectonic
analysis, the main deformation features have been identified and located in both
piedmonts, named from north to south: Las Crucecitas and Vertientes faults (in the
eastern piedmont of the Sierra de La Crucecita) and the Western Talacasto fault
system (in the western piedmont of the homonymous range). The main geological
structures were identified by the analysis and interpretation of gravimetric
anomalies, employing data obtained from World Gravity Map 2012 (WGM12),
which includes earth and satellite gravity data derived from the EGM2008 model.
The gravimetrical response of the crustal blocks that compose the area under study
shows a correlation with the most superficial crustal structure and could be asso-
ciated with the different morphotectonic domains recognized in the region.
Likewise, the chapter on “Morphotectonic analysis in the eastern piedmont
of the Sierra de la Huerta, Sierras Pampeanas Occidentales, San Juan,
Argentina”presents a similar contribution by LM Rothis et al., about a geomor-
phological and morphotectonic analysis that was carried out in the eastern flank
of the Sierra de la Huerta to characterize the available evidence of tectonic activity.
The Andean back arc between 27° S and 33° S is characterized by an intense
seismicity, being the epicentre of the most damaging earthquakes in Argentina.
Those events produced deformation, causing changes on the land surface mor-
phology. Three morphostructural units (mountain, transition and depression) were
recognized. The transition unit shows Quaternary active faulting where eight fault
traces with a NW trend and associated scarps were identified. These evidences of
Quaternary faulting were assigned to the Marayes Fault System. Detailed topo-
graphic profiles perpendicular to the strike of fault scarps allowed to measure main
deformation to the north of the study area. Neotectonic deformation in the Arroyo
Los Papagayos (arroyo=creek, sometimes an ephemeral one) produced anomalies in
its pattern and longitudinal profile. Thus, this study allowed the consideration of the
Marayes Fault System as a potential seismogenic source.
MY Esper Angellieri et al. presented the paper “Morphometric analysis of
river basins using GIS as a basis for peak discharge calculation. Case of study:
Pre-Andean section of National Route 150, Argentina”, which analysed various
morphometric characteristics of basins in order to evaluate debris flood or flash
flood hazards. This study, when properly combined with geomorphology and
geology analyses, helps to elaborate a primary hydrological diagnosis to predict the
approximate behaviour of the river basin at the time of heavy rainstorms. The
chosen area includes a stretch of National Road No. 150 up to the International
Border Pass Agua Negra between Argentina and Chile in a sector of the western
and central Pre-Andean. A total of 122 river basins were identified and delineated,
but only 3 (those of larger surface area) were selected for morphometric analysis
Preface vii
and as a suitable case to evaluate the potential magnitude of flash floods in relation
to their associated hazard level in the region.
The contribution by P Santi Malnis et al., “Distributary drainage systems in
La Huerta Range, western Pampean Ranges, San Juan, Argentina”, comprises
a geomorphological and sedimentological survey of the western piedmont of the
La Huerta range, San Juan (Argentina), showing that there is a north–south trend
change of drainage basin morphometry and facies architecture. The study showed
facies distribution on the systems under study. On Las Chacras river, in the northern
portion of the piedmont, fits with the classical alluvial fan model, with a divergent
net of channels from the fan apex. In the middle portion of the piedmont (the Arenal
and Puquial rivers), alluvial fan facies are also present with aeolian interaction,
triggering disconnection of middle fan facies from distal facies. In the southern
portion of the piedmont, drainage system flows parallel to axial drainage system
(Bermejo River). In the Cañada River, flows keep channelized until its distal
portion in middle to high sinuosity channels that deposit alternate and scroll bars. In
the distal portion, main channel diverge in a distributary net of channels that
develops a fan-shaped deposit characterized by terminal splays and aeolian dunes.
The paper by CE Ginestra Torcivia and NN Ríos López on “Preliminary
morphometric analysis. Río Talacasto basin, Central Precordillera of San
Juan, Argentina”analyses various morphometric characteristics of the Río
Talacasto basin, situated approximately 80 km north-west of the San Juan city, in
the central Precordillera geological province. Various morphometric parameters
were analysed in order to evaluate its flash flood hazard. For this purpose, some
measurements (area, perimeter, length, width, maximum and minimum height and
Strahler order, slope, aspect, curvature and convergence index, topographic position
index, and roughness index) were calculated. These measurements allows future
analysis to predict approximately the behaviour of the basin in the presence of a
series of theoretical rainstorms that may generate unusual runoff volumes. The
importance of this evaluation is that the basin includes the National Route 149 and
the Provincial Route 436, both being the main accesses to the northern and western
portions of the province. The results obtained conclude that the basin has a sig-
nificant susceptibility to the occurrence of flash floods and other landslides.
The paper by EV Ortiz et al., “Risk analysis due to the variation of chemical
parameters induced by lithology in Fiambalá: Chaschuil River, Catamarca,
Argentina”, discussed that, in predominantly semiarid environments, such as the
town of Fiambalá, Catamarca, the water resource directly impacts on the
socio-economic development of the region. The demand of the resource increases
the vulnerability and can produce a deterioration in quality and quantity due to
different environmental and anthropic factors. Therefore, it is necessary to carry out
studies that improve the knowledge of water resources and help a more efficient
planning in the management of these resources for the development and the general
welfare of the population. The Abaucán River is mainly supplied by the Fiambalá
and Chaschuil rivers, the latter being the most important tributary. Lithology affects
the location and exploitation of aquifers; therefore, it is necessary to analyse the
fluvial contributions of the area, the Quaternary deposits, and the physical–chemical
viii Preface
quality of the water that flows over them. From the analysis carried out, it is
concluded that the geochemical alteration due to the lithological influence is almost
negligible, which is why it presents strong performance in the agricultural devel-
opment of the region.
Boretto et al., on the “Identification of knickpoints in littoral basins of
Argentine Patagonia: geomorphic markers in a passive margin”.These authors
analysed the knickpoints that are an expression of disequilibrium in a fluvial sys-
tem, and they occur in both alluvial and bedrock rivers and provide a method for
using knickpoints as geomorphic markers in coastal basins associated with the
Atlantic Ocean coast. However, less attention is paid to the fluvial systems in
well-developed environments along the passive coastal margin as the Atlantic
Ocean coast in Patagonia. For the first time in this region, knickpoint analysis
together with hypsometric curves and longitudinal stream profiles studies was
conducted to understand the landform evolution in coastal basins along the passive
margin in Bustamante and Solano Bays (Chubut province, Patagonia, Argentina)
during the recent past.
E. GarcíaAráoz et al. have contributed a paper on “Granitic caves from the
Achala Batholith in the Province of Córdoba, Argentina: A study on three
particular stories with a common past”.
This paper discussed three caves developed especially in granitic rocks com-
position, which are analysed in order to specify their particular origins and classify
it according to its morphological characteristics and the genetic processes involved.
These caves are located on the same scarp of the rock massif and, therefore, share a
geological and geomorphological common history, which is shown in their
hypothesis of evolution. In addition, based on the type of cavity and certain
observations of their environments, it is possible to establish a relative chrono-
logical order in their ages of formation. In this context, it is proven that these
underground environments (as the other geographical accidents and granitic land-
forms) are not chaotic but—on the contrary—they are structured in geological and
geomorphical processes over time and they respond to a common evolutionary
framework to the entire rock massif.
The paper by JP Velázquez et al., “Scenic and geotouristic potential of vol-
canic landscapes in southern Patagonia: necks, buttes and vents, Santa Cruz
Province, Argentina”,analyses the spatial distribution of volcanic landforms that
compose natural elements, which occur as positive features in the Southern
Patagonia tablelands. In the province of Santa Cruz (Southern Patagonia,
Argentina), an inventory of 106 relevant landforms has been completed: 52 necks,
28 buttes and 26 isolated eruptive centres, which provide a high degree of vari-
ability in the visual components of the landscape. A database has been prepared,
containing information about their geographical position and localization with
respect to the main circulation routes, cities and towns, elevation, relative relief and
geological age. Likewise, a database of satellite imagery and aerial photographs has
been compiled, and thematic cartography was prepared. This information allowed
the identification of the most appropriate sectors in which detailed case studies
Preface ix
could be performed, with the aim of evaluating their scenic possibilities and their
potential to develop activities associated with geodiversity and geotourism.
The paper on “Early human occupations in the valleys of northwestern
Argentina: contributions to dating by the varnish micro-laminations tech-
nique”,by JP Carbonelli et al., presents the results of the micro-laminations of rock
varnish (VML), made on artefacts from a quarry-workshop located in the Santa
María valley, Argentina. The data obtained indicate that the minimum age of
exposure of the surface of these artefacts is 9400 radiocarbon years AP, which
allows us to begin discussing the settlement of the region of the intermontane
valleys of north-western Argentina, throughout the Holocene. The results obtained
through this methodology, mainly the detection of ten humid events throughout the
studied sequence, contribute to the knowledge of the palaeoclimatic variability that
occurred during the Holocene in the study region.
Mirian Collantes
Laura Perucca
Adriana Niz
Jorge Rabassa
x Preface
Acknowledgements
The editors acknowledge the authorities of the 20th Argentine Geological Congress,
in which framework the Symposium on Geomorphology, Quaternary and Climatic
Change studies took place. We also want to thank the authorities of the Argentine
Association of Quaternary Studies and Geomorphology (AACYG) for the support
to the cited Symposium and for sponsoring this volume. We would also like to
thank Springer Nature for accepting our proposal of this publication.
We are greatly indebted to those colleagues and specialists who generously
reviewed the contributions published in this volume: E Aguilera, P Bouza,
E Brunetto, M Cioccale, C Colombi, S Degiovanni, N Doffo, MY Esper Angilieri,
F Hongn, A Mehl, G Ojeda, JL Palacio Prieto, A Rapalini, M Salemme and
J Suriano.
Finally, we want to express our gratitude to the corresponding authors without
whose contribution this volume would not have been possible.
xi
Contents
Relationship Among a Supernova, a Transition of Polarity
of the Geomagnetic Field and the Pliocene-Pleistocene Boundary ..... 1
R. H. Compagnucci, M. J. Orgeira, A. M. Sinito, L. Cappellotto,
and S. Plastani
Neogene Continental Deposits of Bahia Blanca, Argentina.
Palaeoenvironmental and Palaeoclimatic Inferences ................ 40
Silvia C. Grill, Mauro L. Gómez Samus, and Ana L. Fernández
Perched Dunes in the Fuegian Steppe, Southern Argentina:
Archeological Reservoirs of Holocene Information ................. 58
Andrea Coronato, Mónica Salemme, Jimena Oría, Florencia Mari,
and Ramiro López
Morphotectonic and Gravimetric Analysis of the La Burra Valley,
Central Precordillera, San Juan, Argentina ...................... 92
L. P. Perucca, L. M. Rothis, J. Alcacer, N. Vargas, G. Lara,
F. A. Audemard, F. H. Bezerra, and D. L. Vasconcelos
Morphotectonic Analysis in the Eastern Piedmont of the Sierra
de La Huerta, Western Sierras Pampeanas, San Juan, Argentina ..... 114
Luis Martín Rothis, Federico Miguel Haro, Laura Patricia Perucca,
Paula Santi Malnis, Juan Manuel Alcacer, and Nicolás Vargas
Morphometric Analysis of River Basins Using GIS as a Basis for Peak
Discharge Calculation. Case of Study: Pre-Andean Section of National
Route 150, Argentina ....................................... 129
María Yanina Esper Angillieri, Oscar Mario Fernández, Miguel Pereyra,
Carla Ginesta Torcivia, and Natalia Ríos
Distributary Drainage Systems in La Huerta Range, Western
Pampean Ranges, San Juan, Argentina ......................... 136
Paula Santi Malnis, L. Martin Rothis, and Carina E. Colombi
xxvii
Preliminary Morphometric Analysis: Río Talacasto Basin, Central
Precordillera of San Juan, Argentina ........................... 158
Carla E. Ginesta Torcivia and Natalia N. Ríos López
Risk Analysis Due to the Variation of Chemical Parameters Induced
by Lithology. Fiambalá, Chaschuil River, Catamarca, Argentina ..... 169
Erlinda V. Ortiz, Adriana E. Niz, Marcelo E. Savio, and Cinthia A. Lamas
Identification of Knickpoints in Littoral Basins of Argentine
Patagonia: Geomorphic Markers in a Passive Margin .............. 182
Gabriella M. Boretto, Marcela Cioccale, JoséTello, Eduardo GarcíaAráoz,
and Sandra Gordillo
Granitic Caves from the Achala Batholith in the Province
of Córdoba, Argentina: A Study on Three Particular Stories
with a Common Past ....................................... 209
Eduardo GarcíaAráoz, Nicolás Madelón, Micaela Pleitavino,
Gabriella Margherita Boretto, and Marcela Cioccale
Scenic and Geotouristic Potential of Volcanic Landscapes
in Southern Patagonia: Necks, Buttes and Vents,
Santa Cruz Province, Argentina ............................... 233
Juan Pablo Velázquez, Elizabeth Mazzoni, and Jorge Rabassa
Early Human Occupations in the Valleys of Northwestern
Argentina: Contributions to Dating by the Varnish
Micro-Laminations Technique ................................ 262
J. P. Carbonelli and M. M. Collantes
Author Index ................................................ 283
xxviii Contents
Relationship Among a Supernova, a Transition
of Polarity of the Geomagnetic Field
and the Pliocene-Pleistocene Boundary
R. H. Compagnucci
1
, M. J. Orgeira
2,3(&)
, A. M. Sinito
4
,
L. Cappellotto
3
, and S. Plastani
5
1
Universidad de Buenos Aires-CONICET, Buenos Aires, Argentina
rhcompagnucci@gmail.com
2
Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires,
Buenos Aires, Argentina
orgeira@gl.fcen.uba.ar
3
IGEBA, Universidad de Buenos Aires-CONICET, Buenos Aires, Argentina
4
Universidad del Centro de la Provincia de Buenos Aires, Tandil, Argentina
5
IDEAN, Universidad de Buenos Aires-CONICET, Buenos Aires, Argentina
Abstract. After the Middle Miocene, two important climatic changes took
place, consisting mainly of cooling in both hemispheres. One occurred between
7.0 and 5.4 Ma and another at the end of the Pliocene, which marked the
beginning of the Pleistocene in approximately 2.58 Ma. The proposal of this
presentation is to analyze diverse forcings of these climatic changes, such as the
influence of the joint occurrence of reversions of the geomagnetic field and
explosions of a supernova. These events occurred coincidentally with the
cooling of Earth. Also, biological changes in those time intervals are analyzed,
especially the evolution of the Hominins since the oldest hominin fossils. The
characteristics of the Galactic Cosmic Rays, its influence on the climate and its
potential mutogenetic effect were taken into account.
Briefly, according to our analysis, it seems to be evident that together with
other factors, the joint occurrence of the explosion of a supernova at less than
100 pc from the Earth and the weakening and/or reversion of the Geomagnetic
Field was an important factor that promoted these two climatic and ecosystem
changes.
Keywords: Geomagnetic field reversion Supernovae
Pliocene-Pleistocene boundary Paleoclimatology Global changes
Mutations Human evolution
1 Introduction
The scientific community has been interested in detecting and understanding the
forcings that have acted and are acting on climate. There are multiple natural causes.
Orgeira et al. (2016) presented a brief review of the different hypotheses for climate
change, such as solar variability, changes of the Total Solar Irradiance (TSI) received
due to terrestrial orbital changes, length of day variations and volcanic activity.
©Springer Nature Switzerland AG 2020
M. M. Collantes et al. (Eds.): Advances in Geomorphology and Quaternary Studies
in Argentina, SPRINGEREARTH, pp. 1–39, 2020.
https://doi.org/10.1007/978-3-030-22621-3_1
Additionally, Orgeira et al. (2016) and Kitaba et al. (2017), among other authors,
proposed a connection between the variations of the Geomagnetic Field (GF) during
the reversal of its polarity and climatic changes that occurred in the Late Cenozoic. The
mechanism would be linked to the influence of GF over the entrance in the atmosphere
of Galactic Cosmic Rays (GCRs). In turn, the GCRs favor the formation of a low cloud
cover, which would promote the cooling of the planet (the “Umbrella”effect).
2 Paleoclimatology
After the Middle Miocene Climatic Optimum, a Late Miocene global cooling took
place synchronously in both hemispheres (Herbert et al. 2016) (Fig. 1). The Antarctic
glaciations began around 34 Ma under CO
2
levels above 600 ppm (Galeotti et al.
2016). Approximately between 7.0 and 5.4 Ma, the cooling culminated with ocean
temperatures dipping to near-modern values (Fig. 1). The Late Miocene shifts from an
equable climate towards the modern world conditions of strong equator-pole temper-
ature gradients in both hemispheres. The changes in climate, temperature and
ecosystems were a direct consequence of a decline in atmospheric CO
2
(Bartoli et al.
2011, Herbert et al. 2016).
Fig. 1. Global deep ocean temperature in the Cenozoic Era; (a) the past 65 Ma, using d
18
O data
of Zachos et al. (2008), (b) the past 5 Ma (Pliocene and Pleistocene) using Lisiecki and Raymo
(2005) and Atmospheric pCO
2
range estimates (Seki et al. 2010) (Adapted from Jakob 2017).
2 R. H. Compagnucci et al.
During the Pliocene (5.3 Ma to 2.58 Ma), the Earth experienced a transition from
relatively warm climates to the prevailing cooler climates of the Pleistocene. As it was
mentioned before, Lisiecki and Raymo (2005) presented climate data through an
average of 57 globally distributed benthic d
18
O records for the last 5.3 Ma, which
measured global ice volume and deep ocean temperature.
Although the external factors that determine climate were essentially the same, the
Pliocene prior to 3.0 Ma was generally 2–3 °C warmer than today. This period shows
smaller terrestrial and sea ice extent (Haywood and Valdés2004, Jiang et al. 2005), a
partially deglaciated West Antarctic Ice Sheet (Naish et al. 2009) and global sea level
10–40 m higher than today (Raymo et al. 2011). This epoch is characterized by pro-
nounced climatic oscillations and then, there was a cooling during the Quaternary. In
Fig. 1, it is possible to observe the cooling that occurred gradually and in a stepped
way. Warmer and cooler periods occurred throughout the Pliocene, but with an overall
cooling trend.
Climatically, the Pliocene could be divided into three periods: (1) an Early Pliocene
warm period, (2) the Middle Pliocene, a period of sustained global warming, and (3) a
climatic deterioration during the Late Pliocene leading to the high-magnitude climate
variability associated with Pleistocene glacial/interglacial cycles.
The early warm period had climate conditions that were forced by CO
2
concen-
trations. Different evidence determined a gradual decline from CO
2
values of around
410 ppm during the Early Pleistocene to *300 ppm around 3.0 Ma, coinciding with
the start of transient glaciations on Greenland (Bartoli et al. 2011).
Conditions in the equatorial Pacific Ocean were characterized by sea surface
temperature gradient considerably lower than today, and mean sea surface temperature
in the east similar to that in the west. These conditions have been described as a
permanent “El Niño state”or “El Padre”(Fedorov et al. 2006).
This period was marked by a number of significant tectonic events which created
the present landscape. One of these events was the configuration of a continuous land
bridge between the North America and South America tectonic plates. This was the
product of the interplay of several plates, mainly the Caribbean Plate and resulted in a
land bridge, i.e. the Isthmus of Panama, ending the surface water exchange between the
Pacific and Atlantic oceans, known as the Central American Seaway. These changes
had impacts on the evolution of climate through large-scale changes in ocean circu-
lation and could have contributed to the initial intensification of the Atlantic Meridian
Overturning Circulation (AMOC) and the North Atlantic warming prior to 3.6 Ma.
Furthermore, it led to enhance flow of warm and salty surface water into the North
Atlantic via the Gulf Stream (Bell et al. 2015).
However, Hoorn and Flantua (2015), Montes et al. (2015) and Erkens (2015),
among others, claimed that rather than the generally accepted date of *3.0 Ma, the
Panama Isthmus was effectively completed by the Middle Miocene, around 13.0 Ma.
This was disputed by others researchers as Herbert et al. (2016) and O’Dea et al. (2016)
who proposed a younger formation at approximately 2.8 Ma, and a strong criticism
against the uncritical acceptance of the old isthmus hypothesis. It is crucial to determine
the time of closure, mostly because it has been linked to three major events in the
history of Earth: the onset of the Thermohaline Circulation, the onset of Northern
Hemisphere glaciations and the birth of the Caribbean Sea. Recently, Jaramillo et al.
Relationship Among a Supernova, a Transition of Polarity of the GF 3
(2017) rejected both age hypothesis, and claimed that new data are needed to under-
stand the rise of the Panama Isthmus.
The Northern Hemisphere glaciation (NHG) started as early as 3.6 Ma (Mudelsee
and Raymo 2005). The global average temperature in the Middle Pliocene was 2–3°C
higher than today (Raymo et al. 2006, Lisiecki and Raymo 2007, Robinson et al. 2008).
During the Late Pliocene, from 3.5 to 2.58 Ma, the deterioration of the Earth’s
climate state led to an increase in Northern Hemisphere glaciations (Fig. 1). During this
period, the temperature reached values comparable to those of present-day and
Holocene-like climate conditions took place.
The increasing glaciation of Greenland may have been driven indirectly through
variations in atmospheric aerosol concentration or volcanic dust (Prueher and Rea
1998) and/or directly through variations in precession, obliquity and eccentricity orbital
parameters, which produced a decrease in the incoming solar radiation (Milankovitch
1941).
Although Milankovitch forcing has been constant over the past several million
years, the amplitude of the climatic response underwent remarkable changes as the
long-term global cooling introduced different climate feedbacks.
At the Middle Pliocene, around 3 Ma an amplification of the response of climate to
orbital forcing started due to the permanent ice sheets over high latitudes of both
hemispheres (McGehee and Lehman 2012) and the decreasing CO
2
(Willeit et al.
2015).
Development of glaciation required a low insolation during the summer to avoid
full melting of the accumulations of winter snow, as it normally happens in conditions
of great amplitude of obliquity.
The amplitude of obliquity cycles increased for *3.0–2.5 Ma and a strong rise in
the amplitude of precession affected insolation at 60° N, at *2.8–2.55 Ma (Fig. 2).
Both processes may have forced a rapid ice-sheet buildup in the Northern Hemisphere
(Maslin et al. 1998) during the Pliocene-Pleistocene (Neogene-Quaternary) boundary.
The glacial amplitudes of the Northern Hemisphere ice sheets started to present
Fig. 2. Orbital parameters (eccentricity, obliquity and precession) (with information from
Laskar et al. 2004, adapted from Jakob 2017).
4 R. H. Compagnucci et al.
substantial differences between glacial and interglacial periods. This represents a
characteristic of the Quaternary climate (Raymo et al. 2006). The beginning of a
marked cycle of obliquity can be seen (Fig. 2) during the Early Pleistocene in the proxy
temperature series, which is replaced later during the last 1.0 Ma by the cycle of
eccentricity of 100 ka.
Hennissen et al. (2015) listed proxy records evidence of the Northern Hemisphere
major climatic changes around the Pliocene-Pleistocene boundary. The compilation
includes a wide range of data from Hennissen et al. (2014), Kleiven et al. (2002),
Bailey et al. (2013), Naafs et al. (2010,2013), Friedrich et al. (2013), Versteegh et al.
(1996), Thierens et al. (2013), Haug et al. (2005), Martínez-García et al. (2010), Jansen
and Sjøholm (1991), Froese et al. (2000), Duk-Rodkin and Barendregt (2011), Pross
and Klotz (2002), Herbert et al. (2015), Klotz et al. (2006), Ding et al. (2005), Sun et al.
(2006,2010a,2010b), Demske et al. (2002), Melles et al. (2012), Brigham-Grette et al.
(2013) and Andreev et al. (2014). Furthermore, Hennissen et al. (2015) analyzed SSTs
proxy data of the central North Atlantic Subtropical Gyre, and noted that seasonality
increased significantly over the 2.8–2.5 Ma time period. This process would be caused
mainly by the drop in the early spring temperatures while summer temperatures
remained relatively stable. The seasonality tended to peak during glacial intervals and
the maximum occurred at *2.6 Ma, a time when the North Atlantic Current and the
Arctic Front shifted to more southerly positions. According to the present authors, it
seems unlikely that the increase in the seasonality could be explained only by changes
in orbital parameters.
Other causes should be involved in the changes of the Pliocene to the Pleistocene,
as the changes in ocean gateways:
(i) the Central American Seaway that was equivalent to a *5 cm sea-level difference
between the “closed”versus “open”CAS scenario (Lunt et al. 2008),
(ii) the Indonesian Seaway *4.0–3.0 Ma that may have altered atmospheric and
oceanic circulation pattern over the Pacific Ocean (Cane and Molnar 2001, Karas
et al. 2009) causing a cooling and shoaling of the thermocline in the tropical
Indian Ocean. This seaway may have also contributed to the global thermocline
shoaling recorded for the Pliocene (Philander and Fedorov 2003, Wara et al. 2005,
Steph et al. 2006) strengthening the tropical Pacific Walker Circulation and
reducing poleward heat transport. Thereby, favoring high-latitude cooling and the
buildup of extensive Northern Hemisphere ice sheets (Cane and Molnar 2001).
A consequence of these changes was the termination of the “permanent El Niño-like
conditions”during the transition from the warm Pliocene climate state to a climate state
that approximates modern conditions with strong upwelling in the east of the basin and
more developed zonal temperature and primary productivity gradients (Bolton et al.
2010). During the Late Pliocene and the Early Pleistocene, in the equatorial Pacific
Ocean a climatic shift occurred from the “El Niño-like”to the “La Niña-like state”.
According to Philander and Fedorov (2003)“in the tropics and subtropics the response
to obliquity variations is in phase with, and corresponds to, El Niño conditions when
tilt is large and La Niña conditions when tilt is small”.
Additional forcing mechanism was the decrease in carbon dioxide concentrations
(De Schepper et al. 2014). The reconstructed CO
2
record shows that glaciation in the
Relationship Among a Supernova, a Transition of Polarity of the GF 5
northern hemisphere begins once the average long-term CO
2
concentration falls below
265 ppm after a period of strong CO
2
decrease. Different simulations show that
Greenland glaciation was controlled mainly by a decrease in atmospheric CO
2
during
the Pliocene (Lunt et al. 2008, Willeit et al. 2015).
3 Pliocene-Pleistocene Boundary
Lisiecki and Raymo (2005) presented a 5.3 Ma stack of benthic d
18
O records from a
global distribution. Their age model situates the Pliocene-Pleistocene boundary around
2.6 Ma (Marine Isotope Stage –MIS- 104).
According to Bintanja and Van de Wal (2008), the onset of major glaciations in the
Northern Hemisphere, around 2.7 Ma, was most probably induced by climate cooling
during the Late Pliocene. The reconstructed marine isotope signal increased progres-
sively since 3.0 Ma, showing climatic cooling and increase of ice sheets. Its amplitude
also increased with time, with noticeable changes occurring around 2.7 Ma. According
to calculations, the inception of the Northern Hemisphere ice sheets at about 2.7 Ma
may be linked to air temperatures dropping below –5 °C in relation with present time
(Bintanja and Van de Wal, 2008).
Concurrent results are presented by Venti and Billups (2012) who, based on the
North Pacific Ocean first orbital-scale benthic-foraminiferal d
18
O and d
13
C time series
that span the Pliocene-Pleistocene climate transition, found that glacial-interglacial
climate cycles began to impact terrestrial plant habitat in middle latitude North Pacific
Ocean at 2.7 Ma.
It has long been known that global cooling began in the Late Tertiary/Neogene,
with multiple major cooling phases between 2.8 and 2.4 Ma, which vary regionally:
North Atlantic Ocean ice-rafted debris at 2.72 Ma; loess–palaeosol accumulation in
China at 2.6 Ma; severe cooling in northwestern Europe at 2.52 Ma; arrival of sub-
Antarctic molluscs in New Zealand at 2.4 Ma (Gibbard et al. 2010).
In 1996, IUGS ratified a new Pliocene stage, the Gelasian, between the underlying
Piacenzian Stage and the overlying Pleistocene Series. The base of the Gelasian was
defined by a Global Stratotype Section and Point (GSSP) at Monte San Nicola in
southern Sicily and dated by astronomical tuning to 2.58 Ma. This stratotype lies just
1.0 m above the Gauss–Matuyama palaeomagnetic transition (Gibbard et al. 2010, Ogg
et al. 2016).
This transition at the base of the Gelasian was determined by Gibbard and Head
(2009) at 2.58 Ma or 2.60 Ma, based on revised
40
Ar/
39
Ar dating of the underlying
Gauss–Matuyama polarity boundary as 2.61 Ma (Singer 2014).
The base of the Gelasian stage in Sicily is near above the base of reversed-polarity
Chron C2r (Gauss–Matuyama polarity boundary) (Rio et al. 1998, Gibbard et al. 2010).
This level is slightly younger than the 2.6–2.7 Ma (MIS 104 and 110) onsets of the first
major influx of ice-rafted debris into middle latitudes of the North Atlantic Ocean,
deposition of glacial till into middle continent North America, and the major glacial-
caused global sea-level sequence boundary and lowstand (Ogg et al. 2016). Then, the
Gelasian stage and its coincidence with the GF transition Matuyama-Gauss enabled an
unambiguous and precise global marker between continental and oceanic deposits. The
6 R. H. Compagnucci et al.
Quaternary System was defined by the ICS/IUGS at this established
Gelasian GSSP. This level has a recommended age from astronomical calibration of
2.588 Ma (Rio et al. 1998); but other estimates are 2.58 Ma, based on its relative
position within that precession cycle.
4 Geomagnetic Field Reversions
The Geomagnetic Field (GF) has reversed its polarity many times in the geological
past. Particularly, during the Late Miocene and the Early Pleistocene several reversions
of the GF have been recorded (Fig. 3). For the last 6.0 Ma, four Magnetic Chrons are
accepted: the Bruhnes, Matuyama, Gauss and Gilbert chrones, respectively. In addition
to Gauss-Matuyama, Matuyama-Brunhes, and Gilbert-Gauss polarity transitions, there
are eight other reversals boundaries, which may represent instability in the geodynamo
that is associated with a precipitous drop in paleointensity (Singer 2014).
The causes of GF reversals are still not clearly known, although some hypotheses
and models have been presented (among others, Gallet and Pavlov 2016). GF is
accepted to be generated by fluid motions in the liquid, outer part of the Earth’s core,
which is mainly composed of iron. The fluid motions are driven by buoyancy forces
that develop at the base of the outer core as the Earth slowly cools and iron condenses
onto the solid, inner solid core below. The rotation of the Earth causes the buoyant fluid
to rise in curved trajectories, which generate new magnetic field by twisting and
shearing the existing magnetic field. Over 99% of the Earth’s magnetic energy remains
confined entirely within the core. The temporal patterns of dynamo behavior may
reflect physical interactions between the molten outer core and the solid inner core or
lowermost mantle (Singer 2014). These interactions may control reversal frequency
and shape the weak magnetic fields that arise during successive dynamo instabilities.
Particularly, Deino et al. (2006) estimated a calibrated age of 2.610 Ma for the
Gauss-Matuyama reversal, using
40
Ar/
39
Ar ages of two tuffs in normally and reversely
magnetized lake sediments in Kenya.
After the transition, a conspicuous characteristic defined the GF. Ahn et al. (2016)
estimated a weak virtual axial dipole moment of 3.66 (±1.85) 10
22
Am
2
during the
Early Matuyama Chron (inferred time period of 2.34 to 1.96 Ma). It means that the
early stage of the Matuyama Chron can be characterized by a long period of low
geomagnetic field intensity.
Regarding variations of the GF in more recent times, Korte et al. (2018) recently
reconstructed past geomagnetic field morphology and variations based on paleo- and
archeomagnetic data. They improved the Late Pleistocene and Holocene geomagnetic
field models and provided high-quality data.
According to the information compiled and provided for these authors, it is evident
that the intensity of the GF was substantially lower in the Late Pleistocene than during
the Holocene. However, the trend appears to be reversing in the last hundred years.
Measurements of the Earth’s GF have been done practically continuously since about
1840 (Fig. 4). The recorded downward trend of the strength of the dipole moment is
noticeable.
Relationship Among a Supernova, a Transition of Polarity of the GF 7
If this trend continues, the dipole moment may reach near 0 in about 1,500 years
(British Geological Survey, http://www.geomag.bgs.ac.uk). However, this is only one
of the possibilities taking into account the oscillations of the GF in the past. Up to now,
it is not possible to know if the geomagnetic field is beginning a reversal, an excursion,
or simply a variation in GF dipole intensity.
Fig. 3. GF reversion time table, following Cande and Kent (1995), Langereis et al. (2010),
Singer (2014) and Ogg et al. (2016).
8 R. H. Compagnucci et al.
5 Galactic Cosmic Rays Origin and Effects
Particles that bombard the Earth from anywhere beyond its atmosphere are known as
cosmic rays (CRs). They are energetic, subatomic particles that arrive from outside the
Earth’s atmosphere. The basic unit of measurement used in discussing the energy of
CRs is the electron-volt, or eV.
The range of energies encompassed by CRs is truly enormous, starting at about
10
7
eV and reaching 10
20
eV for the most energetic CRs ever detected.
The CRs spectrum in Fig. 5clearly shows that the number of CRs (the CRs flux)
detected drops off dramatically when going to higher energies. The spectrum exhibits a
‘knee’and an ‘ankle’, both of which deviate from the standard exponential decline
(dotted line).
In 1912, Viktor Hess discovered the CRs. After 100 years of mystery, the CRs
origin finally seems to be resolved. Current suggestions are that the CRs with energies
less than about 10
10
eV are primarily solar CRs or solar energy particles (SEPs). They
have a composition similar to that of the Sun, and are produced in the corona by shock
acceleration, or when part of the solar magnetic field reconfigures itself (Mirosh-
nichenko 2001, Reames 2013).
On the other hand, Galactic Cosmic Rays (GCRs) come from outside the Solar
system but generally from within our Milky Way galaxy. They are charged particles
with energies between *10
10
and 10
15
eV. The GCRs helical motion around the
magnetic field lines of the Galaxy causes their distribution to appear isotropic (they are
detected equally in all directions); even though astronomers believe that they originate
in the shocks of supernova remnants (IceCube Collaboration 2013). For the particles of
Fig. 4. Moment of the geomagnetic field from 1900 to present times (modified from http://
www.geomag.bgs.ac.uk). IGRF: International Geomagnetic Reference Field.
Relationship Among a Supernova, a Transition of Polarity of the GF 9
galactic origin, then, the energy comes mainly (but not exclusively) from supernova
explosions which explains the cosmic ray particles at all energies below the ‘ankle’at
310
18
eV (Fig. 5, Helder et al. 2012, Drury 2012, Cardillo et al. 2014).
During periods of intense solar activity - not just during the maxima of the solar
cycles - SEPs may be released in large numbers. Energetic particles from the Sun, as
well as its magnetic field, can scatter GCRs, leading to a much smaller number reaching
Earth, phenomenon known as a Forbush decrease (Cane 2000). On a larger scale, there
is an anti-correlation between the solar cycle and GCRs flux given variations connected
to the *11 yr sunspot cycle and *22 yr solar magnetic cycle (Ahluwalia 1997, Cane
et al. 1999, Mangeard et al. 2018). Variation of GCRs flux is therefore the product of
the solar wind speed and the interplanetary magnetic field strength (Sabbah 2000), with
higher cosmic ray fluxes reaching the troposphere during the solar minima (Carslaw
et al. 2002). The composition of GCRs is slightly different from that of SEPs
and anomalous cosmic rays (ACR) insofar as they are slightly enriched in heavy
elements as well as in lithium, beryllium and boron (Mewaldt et al. 1994). These latter
elements are thought to result from the fragmentation of heavy nuclei during collisions
with interstellar matter, and observations of their composition allow to estimate their
Fig. 5. The flux of cosmic ray particles as a function of their energy. The fluxes for the lowest
energies are mainly attributed to solar CRs, intermediate energies to galactic CRs, and highest
energies to extragalactic CRs. Adapted from Helder et al. (2012)
10 R. H. Compagnucci et al.
age (3–10 million years) and the amount of material traversed on the way to
the Solar System.
Cosmic ray research has recently discovered new sources of ultra-high energy
cosmic rays. The Pierre Auger Collaboration (2017) reported the first observational
evidence that cosmic rays originate from much further away than our galaxy. Eichmann
et al. (2018) discussed radio galaxies as the source of GCRs with energies higher than 6
Joules (39 10
18
eV), namely ultra-high-energy cosmic rays (UHECRs).
Pudovkin and Veretenenko (1995) were the first to mention the possible causal
relationship between the decrease of cloud cover and the Forbush decrease of the GCRs
that occurred following a coronal mass ejection.
However, the correlation between the GCRs flux and the global cloud cover of the
Earth was first postulated by Svensmark and Friis-Christensen (1997). They proposed
the link between the solar variation and climate by changes in the global cloud cov-
erage produced by the variations in the GCRs flux. This was followed by many articles
either rejecting or questioning the link between GCRs flux and cloud formation. Kuang
et al. (1998) using data for 1983–1993 period analyzed variations of cloud optical
thickness and concluded that is not clear if low level cloudiness variations were caused
by the solar cycle or by the El Niño/Southern Oscillation (ENSO) cycle. Sun and
Bradley (2002) suggested that there is not a solid relationship between low cloud
covering and GCRs flux.
Different doubts were expressed by Kernthaler et al. (1999), Kristjánsson et al.
(2000), Wagner et al. (2001), Sloan and Wolfendale (2008), among others. The main
argument against the GCRs link with low cloud formations was the lack of an estab-
lished physical mechanism.
The SKY Experiment to investigate the role of cosmic rays in cloud formation in
the low Earth’s atmosphere, at the Danish National Space Science Center and the
European Organization for Nuclear Research (CERN), produced a comprehensive
verification through the Cosmics Leaving Outdoor Droplets (CLOUD) Project (see
https://home.cern/about/experiments/cloud).
Since the first publication (Duplissy et al. 2010) and up to 2017, there were thirty
publications and ten technical reports on the subject. The most relevant are those from
Kirkby et al. (2011) and Kirkby et al. (2016), both widely cited (741 and 236 citations
respectively). The GCRs effect over cloud formation is now established, despite rig-
orous attempts to disprove it, i.e. the proper scientific method.
Recently, Svensmark et al. (2017) determined the effect of ionization on the growth
of aerosols into cloud condensation nuclei, both theoretically and experimentally.
The hypothesis (Fig. 6) is explained in short by Svensmark in the web page of the
Technical University of Denmark, (http://www.space.dtu.dk/english/news/2017/12/
missing-link-found-between-exploding-stars-clouds-and-earths-climate) as follows
(Fig. 7):
•“Cosmic rays, high-energy particles raining down from exploded stars, knock
electrons out of air molecules. This produces ions, that is, positive and negative
molecules in the atmosphere.
•The ions help aerosols - clusters of mainly sulfuric acid and water molecules - to
form and become stable against evaporation. This process is called nucleation. The
Relationship Among a Supernova, a Transition of Polarity of the GF 11
small aerosols need to grow nearly a million times in mass in order to have an effect
on clouds.
•The second role of ions is that they accelerate the growth of the small aerosols into
cloud condensation nuclei - seeds on which liquid water droplets form to make
clouds. The more ions the more aerosols become cloud condensation nuclei. It is
this second property of ions which is the new result published in Nature Com-
munications (Svensmark et al. 2017)
•Low clouds made with liquid water droplets cool the Earth’s surface.
•Variations in the Sun’s magnetic activity alter the influx of cosmic rays to the Earth.
•When the Sun is lazy, magnetically speaking, there are more cosmic rays and more
low clouds, and the world is cooler. When the Sun is active fewer cosmic rays reach
the Earth and with fewer low clouds the world warms up.”
In the long-term scale, the geomagnetic intensity is controlling the GCR flux on the
Earth, being more intense during the reversals with its weakening of the magnetic field
Fig. 6. Henrik Svensmark’s hypothesis proposed a link between solar wind, cosmic rays, and
cloud cover. When cosmic rays hit the atmosphere, they form ions, which give rise to cloud
condensation nuclei and thereby spur the growth of clouds. An active sun partially shields the
Earth from the normal barrage of cosmic rays, leading to fewer low-altitude clouds. Changes in
cosmic-ray influx do not affect high clouds, as there are always plenty of cosmic rays at higher
altitudes, but fewer cosmic rays penetrate to low altitudes, so increases or decreases due to
changes in the solar wind have more noticeable effects there.
12 R. H. Compagnucci et al.
(Frank 2000, Kitaba et al. 2013). Therefore, the cooling that occurred during or
immediately after a reversal would be associated to the increased of the GCRs (Orgeira
et al. 2016).
Furthermore, Svensmark (2015) suggests that the atomic particles coming from
supernova remnants left by exploded stars appear to play a major part in the transition
to a cool/glacial climate. “It gives an understanding of how changes caused by solar
activity or by super nova activity can affect climate.”
Fig. 7. Schematic relationship representing the effect of the GCRs in the Earth climate. This is
specially connected with increased GCR flux related with supernova explosion, if it is coeval
with weak magnetic field.
Relationship Among a Supernova, a Transition of Polarity of the GF 13
6 Supernovae
There has long been speculation (Schindewolf 1954) that terrestrial mass extinctions
(Bambach 2006, Melott and Bambach 2014) might be related to supernovae.
Supernovae (SN) occur in two main types, named as I and II. Type I is primarily a
result of a small object, such as a white dwarf star, gravitationally robbing gas from a
companion until it becomes too massive to support itself against gravity and collapses.
Type II usually results at the end of the lifetime of a very massive star (much larger
than the Sun). As this type exhausts its fuel, it will swell up and then suddenly collapse.
The rebound results in a blast of light, radiation and a shell of ejected material. The
typical released kinetic energy for the two types is about the same.
Including both types, there are about three SN per century in our galaxy.
There have been a few recorded within historical times (Stephenson 2016), and in
the cases of most of them, a remnant can still be seen, in the form of an expanding shell
of hot gas.
Recent massive-star and SN activity in Earth’s vicinity may be traced by
radionuclides with half-lives of up to 100 million years, if trapped in interstellar dust
grains that penetrate the Solar System. One such radionuclide is
60
Fe (with a half-life of
2.6 Ma), which is ejected in SN explosions and winds from massive stars.
The density and temperature distribution of the interstellar medium (ISM) is highly
variable, superbubbles with typical substructures of about 50–150 pc (pc: parsec is a unit
of length used in astronomical objects, 1 parsec = 3.2616 light-years = 3.0857
10
16
m) having lifetimes of some ten Ma. Several SN explosions over the last 14 Ma or
so shaped the present structure of the local superbubble (the Local Bubble).
Although no mass extinction can be definitively linked to a SN, circumstantial
evidence in the form of the agreement of geographical extinction patterns, with
expectations of atmospheric UV transmission, has been presented for one possible link
to a radiation event (Melott and Thomas 2009). Using available information, Gehrels
et al. (2003) modeled the effects of a hypothetical nearby SN and found that a very
close event (within *8 pc) is necessary for a major mass extinction.
More recently, Breitschwerdt et al. (2016) looked at the
60
Fe deposition history and
trajectories of stars in the Local Bubble. They found that the nearest explosions were at
*100 pc, *2 Ma, showing a consistent picture of the evolution of the Local Bubble
and the
60
Fe deposition in the crust.
Wallner et al. (2016) presented a greatly expanded set of data from three different
deep-sea archives, including four sediment cores, two iron–manganese crusts and two
iron–manganese nodules. This dramatically expanded the amount of available
60
Fe data
and confirmed the same broad picture: two SN events within 100 pc (1.7–3.2 Ma and
6.5–8.7 Ma, Fig. 8), or isotope transport from multiple SN via the moving interstellar
medium. The same parameters are indicated by the closely following publication of the
detection of
60
Fe in lunar samples (Fimiani et al. 2016) and the general chronology
supported by recent direct detection in space (Binns et al. 2016). Schulreich et al.
(2018) showed also a peak actually broader (1.5–3.2 Ma) than indicated by the pre-
vious measurements (Fig. 9). Furthermore, noteworthy is the occurrence of an addi-
tional smaller peak at 6.5–8.7 Ma, whose origin is still unknown.
14 R. H. Compagnucci et al.
7 Galactic Interaction Over the Solar System
The Solar System revolves around the galaxy with one orbit *240 Ma (Svensmark
2006) and carries out an oscillation in the direction perpendicular to the galactic disk,
with a *60 to 70 million years period (Schwartz and James 1984, Rampino and
Stothers 1984). These two movements would produce the galactic interaction with the
Solar System carrying out consequences in the Earth.
One forcing mechanism acting over the Earth climate would take place due to the
Solar System’s oscillation, when the Sun pass through the galactic middle plane about
every *30 to 42 million years (Rampino 2015). Taking into account the last 250 Ma,
several studies have reported a *26–30 million years cycle in mass extinctions and
terrestrial impact crater may exhibit a similar cycle of 31 (Rampino and Stothers 1984,
Lieberman and Melott 2007,2012, Rampino 2015).
In fact, the number of cosmic rays that hit the Earth can increase when the Solar
System is closer to the galactic plane than when it is at a maximum distance (100 pc)
from it. Therefore, the expectation is that climate on Earth would be cooler when the
Solar System is at the galactic middle plane (Svensmark 2006). The impact cratering
record initially turned up evidence for a similar cycle of 28–31 million years (Chang
and Moon 2005, Wickramasinghe and Napier 2008).
The position of the Sun relative to the galactic plane may be inferred from the
distribution of populations of disk stars. According to Bahcall and Bahcall (1985) the
last Sun passage through the galactic plane occurred in the past 3 Ma, if the present
Fig. 8. Results from ferromanganese crust measurement showing a peak in
60
Fe/Fe and
ferromanganese (FeMn) crusts incorporation rates adapted from Knie et al. (2004) and Wallner
et al. (2016) respectively.
Relationship Among a Supernova, a Transition of Polarity of the GF 15
position of the Sun is between 0 and 20 pc above the plane. Rampino and Haggerty
(1996) evaluated the pulses of asteroids or comets impacts in the last 2–3 Ma. Hum-
phreys and Larsen (1995) suggested, using star count information, a distance of
20.5 ±3.5 pc above the galactic plane. More recently, Weissman (2014) proposed 52
to 74 million years of period and ±49 to 73 pc of amplitude for the harmonic per-
pendicular movement of the Solar System through the galactic plane, and the occur-
rence of the last passage about 2–3 Ma. However, he indicated the uncertainty in the
values that could be due to the uncertainty in the content of dark matter in the galaxy.
A new analysis by Karim and Mamajek (2016) obtained values consistent with the true
median of 55 previous estimates published over the past century of the Sun’s height
above the galactic middle plane (17 ±2 pc). Reed (2005) results of 19.5 + 2.2 pc,
agrees well with various other determinations cited in his paper. According to the
mentioned contributions, the Solar System could have crossed the plane of the galaxy
around or before the Pliocene-Pleistocene boundary, which could explain, at least in
part, the cooling that occurred through the increasing flow of GCRs. The speed of the
Sun in the vertical direction is well measured, but the distance from the Sun to the
galactic plane is not.
The other potential forcing over the Earth climate would be the Solar System
passage through one spiral arm; its potential importance was noted in the late 1970s
and early 1980s (Napier and Clube 1979, Clube and Napier 1984, Raup and Sepkoski
1984). The Milky Way has four spiral-arms (Englmaier et al. 2009). The lapse between
spiral arms was considered 140 million years (Svensmark 2012). Presently, as shown
in Fig. 9, the Solar System is located in the small arm Orion-Spur, between the
Sagittarius-Carina and Perseus spiral-arms (Gies and Helsel 2005).
Shaviv (2002,2003) and Shaviv and Viezer (2003) argued that the exposure of the
Earth to the increased flow of cosmic rays during the incursion through the spiral arm
of the galaxy correlates with the extended cold periods on Earth. Spiral arms are
regions of stellar formation (Foyle et al. 2010). Therefore, they are regions where stars
Fig. 9. The motion of the Sun in our outer spiral-arm location in the Milky Way. Solar System
traveling through spiral arms in the Milky Way Galaxy. It is currently located near the Orion arm
(yellow), between two major arms: Perseus (green) and Sagittarius-Carina (blue). The diameter of
the Milky Way is about 100,000 light-years and the Sun is located about 28,000 light-years from
the Galactic Center (adapted from Brink 2015).
16 R. H. Compagnucci et al.
that end their lives enlarge the probability of interaction and molecular-dust clouds and
supernova remnants are more likely to appear.
The amount of matter inside the galactic arms is more than on the outside. The
gravitation influence of this matter attracts the inflow of comets to the Solar System. It
results in an increase in concentration of interplanetary dust in the zodiac cloud (lo-
cation of cosmic dust particles which occur along the Ecliptic plane), and a cooling of
the Earth’s climate (Brink 2015). Consequently, the increase of cosmic rays flux reach
a maximum after each encounter with a spiral arm, and then went to a minimum in the
dark spaces between the arms.
During the last 520 Ma, the Solar System crossed the galaxy arms approximately
four times. Therefore, there were four alternating warming and cooling periods with
temperature changes of more than 5.0 °C. Figure 10 shows the d
18
O proxy data of
Earth’s temperature from the Phanerozoic database covering the last 500 Ma. The
abundance of
18
O in fossils is linked to the ocean water isotopic ratio. The
18
O in the
ocean is enriched when
16
O water preferentially evaporates, and it is locked up in ice.
The violet curve is a 60 million years low pass filtered data. The light blue curve is
a low passed filtered, 1/20 million years. These proxy data reflect changes in tem-
perature of the Oceans (*2.0 °C). The *140 million year period had already been
connected to the passing through the spiral arms of the Milky Way (Shaviv 2002,
Shaviv and Veizer 2003, Benjamin 2008, Shaviv et al. 2014).
Fig. 10. d
18
O proxy data from the Phanerozoic database according to Veizer et al. (1999)
(adapted from Svensmark 2006).
Relationship Among a Supernova, a Transition of Polarity of the GF 17
In Fig. 10,a*30 million year period is visible. It had already been demonstrated
by Prokoph and Veizer (1999) that there is a *32 million years variation in the
geological proxy data that could be related to the crossing of the galactic plane.
From paleoclimate data, Svensmark (2006) determined several features of two most
recent spiral arm passages. He restricted to modulation of time scales between 20–
60 Myr, much shorter than the characteristic time for spiral passage 140 Myr. His
results were in agreement with the preceding reported properties of the Milky Way
given additional confidence in the significance of CRs variations and their influence in
climate. There were authors such as Overholt et al. (2009) that, based on new data of
the structure of the galaxy, conclude that there is no evidence to suggest any correlation
between the transit of our Solar System through the spiral arms of our galaxy and the
terrestrial climate. In contrast to other published studies, Overholt et al. (2009) model
does not force azimuthal symmetry into the spiral-arm structure. The asymmetry of the
arms near the solar circle erases any correlation to the 140 million years cycle and any
periodic trend less than the orbital period of our Solar System relative to the spiral
pattern as a whole. Bailer-Jones (2009) reviewed the passage of the Sun through the
galactic midplane or the spiral arms with respect to the evidence for and against the
relevance of these mechanisms for climate change and evolution. The cited author
noted the need to include in the on-going research a critical evaluation of the time series
analysis techniques and hypothesis testing. The analysis suggests that galactic mid-
plane and spiral arm crossings have little impact on biological or climate variation
above background level. Non-periodic impacts and terrestrial mechanisms (volcanism,
plate tectonics, sea level changes), possibly occurring simultaneously, remain likely
causes of many environmental catastrophes. Internal dynamics of the biosphere may
also play a significant role.
However, in the recent presentation of Boulila et al. (2018), long-term cyclic sea-
level variations were quantified statistically from a Phanerozoic dataset that provided a
rare longer-term and continuous record of geological parameters. They showed that
some detected sea-level periodicities are of the same order as those predicted for the
Solar System motions in the galaxy. They showed a statistically significant prominent
and persistent *36 million years sedimentary cyclicity superimposed on two mega-
cycles (*250 million years) in a relatively well-constrained sea-level record of the past
542 million years.
While the *72 million years vertical period was very robust, the *250 million
years period through radial variation of the Sun orbit still requires some fine tuning.
Briefly, it is possible to say that the climate cooling would be caused by the two
movements of the Sun, since both lead to an increase in cosmic rays that may affect
cloud formation. The bigger intensity of cosmic rays and higher density of space dust,
both lead to increase of cloudiness and decrease of planetary surface temperature.
It is necessary to note that both mechanisms derived from the Solar System
movement around and through the galaxy plane are theoretical models. These models
are only constrained by the measurements of present observational velocity of the Sun,
with respect to an inertial frame, as proposed by Schönrich and Binney (2009). Bovy
(2017) presented a detailed new star inventory of the galaxy in the vicinity of the Solar
System; it agrees with and extends the previous studies. This is a good beginning to
map the galaxy with the full set of Gaia data.
18 R. H. Compagnucci et al.
8 Galactic Cosmic Rays Mutogenetic Effect
Initially, Muller (1927) suggested the relation between the incidence of energetic
particles and the mutations. The question asked by Babcock and Collins (1929)“Does
cosmic radiation have any influence on rate of mutation?”, however, received little
attention.
Only speculative hypothesis was produced by Krassovskij and Šklovskij (1958)
with respect to periods of many hundred years when the flux of cosmic rays on the
Earth will be hundred times larger than the mean common conditions. They argued that
it is necessary to recognize that the increase of cosmic rays due to supernovas at certain
stages of evolution could have important, if not decisive, significance. They also
supposed that a significant increase in cosmic rays flux that could be prolonged for
millennia may involve catastrophic consequences for many specialized animal species
with comparatively small population.
Curtis and Smith (1963) observed a light increase in chromosomal deletions in corn
seeds affected by heavy CR particles. Most of CRs energy arrives to the ground in the
form of kinetic energy of muons. Micke et al. (1964) tested the mouns mutation action
over dormant seeds.
Sagan (1973) remarked how important the effect of cosmic rays on Earth’s atmo-
sphere is, and that these rays can produce significant changes as well, such as mutations
in the hereditary material.
More recent researches have shown that a strong increase in the flow of CR can
produce mutations in living organisms and may affect biodiversity by direct or indirect
mechanisms (Medvedev and Melott 2007, Melott and Thomas 2009). These mutations
are the effects of: (i) direct radiation mainly through the muons (McNulty et al. 1974,
Atri and Melott 2011), (ii) the significant climatic change induced by the increase in
cloudiness through the seeding of ionization that produce cooling (Hadly et al. 2004,
Kozma et al. 2016; see Sect. (4), (iii) the effects on atmospheric NOx chemicals and
their precipitation as nitric acid (e.g. Nguyen et al. 1992), and (iv) the DNA
(deoxyribonucleic acid) changes due to the increase in solar UVB (ultra-violet radiation
at 280-315 nm), schematically shown in Fig. 11, as a consequence of ozone depletion
due to ionizing radiation in the atmosphere (Gehrels et al. 2003).
Fig. 11. Changes in the DNA of the genome due to UV light from the sun.
Relationship Among a Supernova, a Transition of Polarity of the GF 19
Despite previous researches, the question continues in the 21st century: “Is there a
connection between enhanced rate of cosmic rays and the origin of life? Have the
variations in cosmic ray flux affected the evolution of life on Earth?”(Atri and Melott
2014).
However, some advances may start to produce an answer. Briefly, SN remnants are
considered the major source of the increased CR flux into the Earth. The radiation that
arrive to the land consists primarily of neutrons and muons which would have a
substantial effect on cancer and mutation rates and the larger and longer-lived organ-
isms would experience a greater relative increase in radiation dose.
The terrestrial effects of both photon and charged particle radiation from super-
novae 50–100 pc from Earth have been modeled by Thomas et al. (2016) and Melott
et al. (2017a).
Thomas et al. (2016) ask whether such SNs are expected to have had substantial
effects on the terrestrial atmosphere and biota. Combining photon and CR effects, they
find that a SN at less than 100 pc can have substantial effect on terrestrial organisms.
Troposphere ionization will increase by nearly an order of magnitude for thousands of
years. The mouns irradiation will increase, twenty times which will approximately
triple the overall radiation load on terrestrial organisms.
In the case of a supernova at 50 pc, as they were at about 2.7 to 1.7 Ma (Pliocene-
Pleistocene boundary) and at 6.5 to 8.7 Ma at the Late Miocene, muon irradiation on
the ground may have increased by a factor of about 150 to 2000 (Melott et al. 2017a,
2017b).
The SN irradiation of muons in the soil and hundreds of meters to the ocean would
increase cancer and the rate of mutation. Especially large and long-lived organisms are
susceptible to developing cancer (Melott and Thomas 2018).
Ancient pathogenic DNA was evidenced by the record of abnormal growth in a
1.6–million- to 1.8-million-year-old toe bone produced by a malignant tumor. Onco-
genesis has been in existence in the hominin lineage for at least 2 million years (Odes
et al. 2016, Randolph-Quinney et al. 2016). New research associated a long-term
exposition to GCR with the present time cancer mortality in São Pablo (Vieira et al.
2018).
The potential biological impacts at Earth’s surface of stratospheric ozone depletion
caused by SN nearby at 50 pc, as it occurred about 2.5 and 8.0 Ma ago, was inves-
tigated by Thomas (2018). He used ionization profiles for three-time frames following
arrival of SN CR. The results of the simulation of the CR ionization were compared to a
control run without SN CR input. Since the runs are not connected to any particular
dates, all time values are arbitrary and given simply to provide scale of the time frames
involved. In the simulation, the UVB irradiance is increased by a factor of 1.1 to 2.8,
with large variation in latitude and seasonally at high-latitude regions (Fig. 12).
Changes in UVA (ultra-violet radiation at 315–400 nm) and PAR (400–700 nm, vis-
ible light) are much smaller.
20 R. H. Compagnucci et al.
A ratio plot for DNA damage (from Setlow 1974) versus ratio of the SN CR case to
the control run is shown in Fig. 13. The DNA damage (in vitro) is increased by factors
similar to UVB, while other biological impacts (erythema, skin cancer, cataracts,
marine phytoplankton photosynthesis inhibition and plant damage) are increased by
smaller amounts. However, the effects on organisms from changes in irradiance can be
quite complicated and in most cases are strongly wavelength-dependent. He concludes
that biological impacts due to increased UV irradiance in this SN case are not at a mass-
extinction level but might be expected to contribute to changes in certain species
abundance. This result fits well with species turnover observed around the Pliocene-
Pleistocene boundary.
Although, as it was already mentioned, ozone depletion and the increase in haz-
ardous UVB have an important biological impact, new effects come to the foreground
(Mellot and Thomas 2018). Muon irradiation on the ground and hundreds of meters
down into the ocean will increase cancer and mutation rates, the differences being most
notable in terrestrial megafauna and benthic organisms. Typically, larger organisms
live long enough to develop cancer; in microorganisms, the primary effects would be
associated with mutation rates. Atmospheric ionization in the troposphere will greatly
increase lightning rates, with a concomitant increase in the rate of wildfires.
With respect to the enhanced mutations, it should be noted that the *8.0 Ma SN
was roughly contemporaneous with the oldest Graecopithecus, dated at around 7.2 Ma.
The oldest remains attributed to Hominini are coeval with about 2.7 to 1.7 Ma SN.
Contemporaneously hominin brain size began to increase (Homo erectus), as it can be
seen in Sect. 8.2.
Fig. 12. The increase in UVB (as a ratio of the SN case to the control run) as a function of time
and latitude (adapted from Thomas 2018).
Relationship Among a Supernova, a Transition of Polarity of the GF 21
8.1 Fauna Extinctions
Traditionally, there was a consensus in placing the Pliocene-Pleistocene boundary at
the base of the Calabrian stage, due to the first appearance of cold fauna from the North
Atlantic Ocean in the Mediterranean Sea. This was interpreted as the first indication of
climatic deterioration in the Northern Hemisphere. However, it is now known through
stable isotopes analyses that a major cooling occurred earlier, around 2.55 Ma (Cita
2008), and even earlier cooling events are known (Cohen and Gibbard 2010).
From a biostratigraphic point of view, the Lowest Occurrence (LO) of some taxa
occurs close to the Piacenzian-Gelasian boundary (ICS 2017). It could mention that
during the Pliocene-Pleistocene turnover, 18 coral genera were lost from the Caribbean
region. As an example, large colonies of Pocillopora and Stylophora highly vulnerable
to the climate shifts in the Pliocene-Pleistocene were extinct (Klaus and Budd 2003).
Furthermore, nannofossils that are one of the best biostratigraphic tools in open
oceans, also showed extinctions rate. In this case, there are the LO of Discoaster
pentaradiatus Tan (2.39 Ma) and the LO of D. surculus that took place at 2.53 Ma
(Agnini et al. 2017, Young et al. 2017, Rio et al. 1998). Regarding foraminifera, a
marker of this boundary is Globoconella puncticulata (Deshayes 1832) (= Globorotalia
puncticulata) which reached its extinction level at 2.35 Ma (Wei 1994).
Pimiento et al. (2017) recognized extinction events among marine megafauna
during the Pliocene-Pleistocene transition. The extinction rates were three times higher
Fig. 13. Ratio of surface-level DNA damage (in vitro) in the 300 yr SN case compared to a
control run, as a function of time, at latitudes between 5° and 55° N (adapted from Thomas
2018).
22 R. H. Compagnucci et al.
than in the rest of the Cenozoic, and with the highest rates occurring during the Late
Pliocene (between 3.8 and 2.4 Ma). The only exception for these times were seabirds
that presented their maximum extinction during the Paleocene. The fossil megafauna
record revels that 36% of genera of this fauna became extinct during the Pliocene,
being the marine mammals the most affected, losing 55% of their genetic diversity.
Meanwhile, seabirds lost 35%, sea turtles 43% and sharks 9%. Pimiento et al. (2017)
found that the marine regression caused a sharp drop in neritic areas during the Late
Pliocene (in coincidence with the highest extinction rates found). This reduction in
coastal habitat, probably acting alongside oceanographic alterations such as changes in
productivity and ocean circulation, was the most likely extinction driver for the Plio-
cene marine fauna.
The ecological preyscapes that energetically support gigantism only arose in the
Pliocene-Pleistocene, with the onset of seasonally intensified upwelling regimes (Slater
et al. 2017).
8.2 Hominin Evolution
Graecopithecus would be the oldest known hominin and the oldest known crown
hominine, as the evidence for the gorillin status of Chororapithecus is much weaker
than the hominin status of Graecopithecus (Fuss et al. 2017). The fossils were dated at
around 7.2 Ma, which would make them the oldest remains attributed to Hominini,
even older than Sahelanthropus tchadensis dated at around 6.0–7.0 Ma (Benoit and
Thackeray 2017, Fuss et al. 2017). This age agrees with genetic estimates calibrated by
mutations per generation, which place the human-chimpanzee split as early as 8.0–
7.0 Ma (Langergraber et al. 2012), but slightly precedes genetic estimates calibrated
using the fossil record, which suggest the split occurred after 6.3 Ma (Patterson et al.
2006).
From at least 6.0 to 3.0 Ma, early humans combined apelike and humanlike ways
of moving around. Fossil bones record a gradual transition from climbing trees to
walking upright on a regular basis. Australopithecus africanus is the first of an early
ape-form species to be classified as hominin (Dart 1925) which apparently evolved in
eastern Africa around 4.0 Ma before spreading throughout the continent and eventually
becoming extinct at 2.0 Ma. The oldest direct evidence of stone tool manufacture
comes from Gona (Ethiopia) and dates between 2.6 and 2.5 Ma, being attributed to
Australopithecus afarensis (McPherron et al. 2010). The curved spine is uniquely
human. Lower back absorbs shock when humans walk and there was a similar curve in
the spine of Australopithecus africanus, who walked upright in a way very similar to
modern humans (Willams et al. 2013, Tardieu et al. 2017). However, the brains of most
species of Australopithecus were roughly 20% larger than the average cranial capacity
in modern chimpanzees (DeSilva 2011).
It is now clear that key events in human evolution occurred within the time interval
that also encompassed the Pliocene–Pleistocene boundary (i.e., within the limits of the
Matuyama paleomagnetic chron, from 2.6 to 0.8 Ma) (Fig. 14). It was during that time
that the genus Homo first appeared in Africa. Two different Homo species appeared.
Homo habilis, who lived at the beginning of the Pleistocene (Leakey et al. 1964), had a
cranial capacity slightly less than half of the size of modern humans. Homo habilis
Relationship Among a Supernova, a Transition of Polarity of the GF 23
coexisted with Homo erectus (meaning “upright man”) for a substantial period after
2.0 Ma. Although it is commonly assumed that this species dispersed out of Africa, it is
possible that it first evolved in Asia. Dennell (2008) explain that it is possible that H.
erectus originated in Southwest Asia from a population that left Africa before 2.0 Ma,
and then dispersed back into East Africa as well as eastwards to Java and China. From
around 1.9 Ma Homo erectus started to spread in Africa, Europe, South and South East
Asia. Depending upon which dates are preferred, early Homo was at Dmanisi by
1.85 Ma, and in Central China (Lantian Gongwangling) at 1.63 Ma, in Java by 1.5 Ma,
and in the Iberian peninsula by 1.2 Ma.
Spoor et al. (2007) confirmed the distinctiveness of H. habilis and H. erectus,
independently of overall cranial size, and suggested that these two early taxa co-existed
in eastern Africa for nearly half a million years in the same lake basin.
The size and broad shape of the hipbones of Homo erectus are similar to those of
modern humans, showing that this early human species had given up climbing for
walking (Ward et al. 2015, Tardieu et al. 2017). Pelvic and proximal femoral mor-
phology in early Homo (namely H. erectus) was uniquely derived (Churchill and
Vansickle 2017). Therefore, Homo erectus shows adaptations of long distance running.
During the evolution of Homo erectus, there was a significant increase in their body
size compared to earlier hominids.
Fig. 14. (a) Evolution of the Homo brain size through time (Adapted from Calvin 2016);
(b) Proxy of ocean temperature showing ice age fluctuations in climate, averaged over 57
sediment-core sites (adapted from Lisiecki and Raymo 2005).
24 R. H. Compagnucci et al.
One of the most distinct features of human evolution is the trend towards
increasingly large brains. The rapid three-fold enlargement of the hominin brain began
about 2.3 Ma (Calvin 2016). Early hominin Australopithecines had a cranial capacity
(CC) slightly larger than that of extant apes (Robson and Wood 2008).
As the Pleistocene cooling began 2.5 Ma, the hominin brain size began to increase
and inexplicably doubled over the next million years. The scatter plot of hominin brain
size over time (Fig. 14) shows major features: firstly a long period of near-stasis in the
Pliocene where brain size in the Australopithecines remained stable; secondly, a fast
3.3 times increase during the Pleistocene up to present times. The tendency towards the
increase started near 2.0 Ma or before.
Most explanations for hominin brain size increase have been focused on micro
evolutionary mechanisms. These hypotheses can explain anagenetic patterns but may
not be relevant for patterns caused by origination and extinction (Gould 2002, Simpson
2016). Patterson et al. (2017) also related the Hominid change, primarily to differences
in dietary ecology.
The results of Schroeder and Ackermann (2017) indicate that for 95% of taxon
comparisons, throughout the cranium (face, maxilla, neurocranium, temporal, mand-
ible), showed that most of the phenotypic cranial and mandibular diversity within
Homo, from *2.8 Ma, is consistent with random genetic drift. These authors also
proposed that it is necessary to reconsider the traditional view that selection was the
main evolutionary process driving changes in the neurocranium, and most other cranial
regions, within Homo, and to consider the implications of that for our understanding of
how and why our lineage evolved.
Campisano et al. (2017) carried out the Hominin Sites and Paleolakes Drilling
Project (HSPDP) to explicitly explore key hypotheses linking environmental history
and mammalian (including hominin) evolution and potentially develop new testable
hypotheses. The results improved the environmental history of eastern Africa during
much of the Late Neogene and Quaternary even if they cannot refute particular
hypotheses of environmental-evolutionary linkages. They demonstrated that temporal
correlation does not prove causation in evolutionary history, but they note that a lack of
correlation in multiple, well-constrained records is prima facie evidence against any
particular hypothesis. There is also the possibility that environmental changes cannot
be linked with observed events in faunal evolution. Competitive environmental
hypotheses would be false in some cases. Non-ecological factors (for example, sexual
selection, and competition, among others) may have been paramount in the evolution
of hominids.
Du et al. (2018) emphasize that origination and extinction were also important in
shaping endocranial volume (ECV) patterns at the clade level, and both micro- and
macro-evolutionary change influenced hominin brain size to different extents at dif-
ferent times. They noted that almost all the first and last appearances are associated
with an increase in average clade-level brain size, and the importance of each is
staggered in time. The changes, as occurred in the appearance of large-brained species,
were mostly from ca 2.3 to 1.7 Ma. According to Du et al. (2018) the complicated
multi-causal nature of hominin endocranial volume or ECV evolution need future
hypotheses and models to recognize and incorporate this hierarchical complexity.
Relationship Among a Supernova, a Transition of Polarity of the GF 25
Therefore, new, comprehensive theories to explain potential influences on hominin
brain size evolution must be constructed.
As it can be seen in the final discussions, it is herein proposed that the conjunction
of the explosion of the supernova and the weakening of the Earth’s magnetic field
would have produced a strong global change with climate-ecological consequences,
plus an increase in the flux of GCR and neutrinos, both with probably mutogenetic
effects.
9 Discussion and Conclusions
In a succinct summary, the analysis of this contribution considers the influence of GF
weakening or/and reversions together with SNs explosions close than 100 pc. These
SNs occurrence is likely to happen because of the Solar System location in one arm of
the galaxy (Sect. 7). These forcing could promote climate changes, biotic variations,
mutations and human evolution that occurred in the Earth history since the Middle
Miocene.
The major cooling event during the Pliocene took place at 3.3 Ma, in Marine
Isotope Stage (MIS) M2 (during the Mammoth reversed polarity subchron). During the
Late Pliocene, from 3.5 to 2.58 Ma, deterioration in Earth’s climate state led to an
increase in Northern Hemisphere glaciations (Sect. 2). Furthermore, ecosystems
changes (Sect. 8.1) occurred together with the earliest Homo erectus found in sedi-
ments assigned to this period in Africa (Sect. 8.2). The changes in ocean gateways led
to the climatic shift during the Pliocene and the Pleistocene (Sect. 2). However, it is
necessary to keep in mind that these important and relatively sudden change could also
be explained by the conjunction of two haphazard factors, which are the explosion of a
SN at *2.7 to 1.7 Ma (Sect. 6) and the geomagnetic weakening due to the Gauss-
Matuyama reversal (Sect. 4). The SN provided the strong increase of the GCR flow,
and a weak geomagnetic field during the Early Matuyama Chron, allowed the entry of a
greater flow of the GCR into the atmosphere. Another hypothesis proposed that the
Solar System could have crossed the plane of the galaxy around or before the Pliocene-
Pleistocene boundary (Weissman 2014 and Sect. 7), which would explain, at least
partly, the cooling that occurred through the increase flow of GCRs. As explained in
Sect. 5, low cloudiness increased in suchs way, causing the start of a greater cooling
that continued increasing by a process of feedback with the ice. The enhanced cloud
formation created an increase of the reflection of solar energy back into space, which
was thus connected to a subsequent cooling of the Earth’s atmosphere. This cooling
promoted the formation of continental glaciers and therefore a significant drop in sea
level with the interplay of further influences like orbital parameters of the Earth. The
increased ice surface over the Earth also amplified the Milankovitch signal on the
climate, characteristic of the Pleistocene.
The same mechanism could have occurred during the Late Miocene-Early Pliocene.
Approximately between 7.0 and 5.4 Ma, the Miocene cooling culminated with ocean
temperatures dropping to near-modern values (Sect. 2). The changes in climate, tem-
perature and ecosystems were a direct consequence of a decline in atmospheric CO
2
(Sect. 2). However, other factors need to be considered because frequent reversals of
26 R. H. Compagnucci et al.
GF (Sect. 4) together with SN explosion (Sect. 6) took place concurrently. Therefore,
the enhanced GCRs due to the SN together with the weakening of the GF that lead the
considerably increased of the GCRs input on the Earth atmosphere producing a cooling
effect on the climate (Sect. 2).
The SN events occurred around 6.5–8.7 Ma and 1.7–3.2 Ma, which coexisted with
the collapse of the GM field, implied that a large GCR flow entered the Earth atmo-
sphere. Then, the mutagenic effects (Sect. 8) of the GCRs, in conjunction with other
factors due to climatic and environmental changes, could have led to an important step
of human evolution. During the first mentioned event, the divergence between the
chimpanzee and hominini (coeval with the started cooling at 7–6 Ma; Lebatard et al.
2008, Simpson et al. 2015) took place. Through the second, the hominini showed a big
number of mutations being the most relevant the rapid enlargement of the brain that
began about 2.3 Ma (Calvin 2016) (for more detail see Sect. 8.2.).
Therefore, the two main Earth´s climate changes occurred during the Late Miocene
and the Pliocene-Pleistocene boundary. This lead us to hypothesize that the occurrence
of the explosion of a SN at a distance of 100 pc or less might have been responsible for
the increase in GCRs together with the reversal and significant weakening of the GF,
for the occurrence of climate cooling, mutations, extinctions and evolution of the
species.
The first SN recorded by humans occurred *5000 years ago. Iqball et al. (2009)
presented evidence in two sites that the ancient inhabitants of Kashmir definitely noted
and registered, at a date between 7,000 and 3,000 BP, different celestial events that
could be related to a SN explosion. According to the authors, the SNs candidates are
HB9 and G182.4 + 4.3 are shell-type SNs remains and as such, they lack pulsars. But
this SN HB9 is estimated to have exploded at around 1.0 kpc (Araya 2014), that is 10
times farther than was postulated to be necessary for the biological and climatic effects
depicted previously. Furthermore, the intensity of the GF was substantively lower in
the Late Pleistocene than during the Holocene, when the possible SN event was taking
place. Therefore, the GCRs flux could had the “umbrella”effect of the GF that pre-
vented the increased the input in the atmosphere as in the two previously situations
described above.
For the above mentioned SNs which occurred during the Holocene, they are
lacking of at least two conditions necessary for the explosions of SNs to affect the Earth
as in the past. One that they must occur nearby, it means 100 pc or less, and another
that the GF must be weakened and / or near zero due to the occurrence of a reversion.
Acknowledgements. The authors wish to express their deepest gratitude to the institutions that
financed the present contribution, the National Council of Scientific and Technical Research of
Argentina (CONICET), the University of Buenos Aires (UBA) and the National University of the
Center of Buenos Aires Province (UNCPBA), Argentina. The present authors also appreciate the
critical reading and the relevant contributions of Dr Augusto Rapalini (UBA), who reviewed a
previous draft of this paper.
Relationship Among a Supernova, a Transition of Polarity of the GF 27
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