Microbial habitability of the Hadean Earth during late heavy bombardment

University of Colorado, Department of Geological Sciences, 2200 Colorado Avenue, UCB 399, Boulder, Colorado 80309-0399, USA.
Nature (Impact Factor: 41.46). 06/2009; 459(7245):419-22. DOI: 10.1038/nature08015
Source: PubMed


Lunar rocks and impact melts, lunar and asteroidal meteorites, and an ancient martian meteorite record thermal metamorphic events with ages that group around and/or do not exceed 3.9 Gyr. That such a diverse suite of solar system materials share this feature is interpreted to be the result of a post-primary-accretion cataclysmic spike in the number of impacts commonly referred to as the late heavy bombardment (LHB). Despite its obvious significance to the preservation of crust and the survivability of an emergent biosphere, the thermal effects of this bombardment on the young Earth remain poorly constrained. Here we report numerical models constructed to probe the degree of thermal metamorphism in the crust in the effort to recreate the effect of the LHB on the Earth as a whole; outputs were used to assess habitable volumes of crust for a possible near-surface and subsurface primordial microbial biosphere. Our analysis shows that there is no plausible situation in which the habitable zone was fully sterilized on Earth, at least since the termination of primary accretion of the planets and the postulated impact origin of the Moon. Our results explain the root location of hyperthermophilic bacteria in the phylogenetic tree for 16S small-subunit ribosomal RNA, and bode well for the persistence of microbial biospheres even on planetary bodies strongly reworked by impacts.

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Available from: Oleg Abramov, Apr 08, 2014
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    • "Lepland et al., 2005; McKeegan et al., 2007). If the first biosphere came into being in the Hadean it would have done so in the context of asteroid and comet bombardment that should have strongly modified the early crust and by extension , affected the nascent biosphere (Abramov and Mojzsis, 2009). Yet, only after the onset of the Eoarchean at about 3850 Ma (Bleeker, 2004) does the geologic record yield direct examples of hydrosphere-crust interactions via the preservation of the oldest rocks of sedimentary protolith (Nutman et al., 1997; Cates and Mojzsis, 2006; Manning et al., 2006; Mloszewska et al., 2012). "
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    ABSTRACT: The oldest compiled U–Pb zircon ages for the Acasta Gneiss Complex in the Northwest Territories of Canada span about 4050–3850 Ma; yet older ca. 4200 Ma xenocrystic U–Pb zircon ages have also been reported for this terrane. The AGC expresses at least 25 km2 of outcrop exposure, but only a small subset of this has been documented in the detail required to investigate a complex history and resolve disputes over emplacement ages. To better understand this history, we combined new ion microprobe 235,238U–207,206Pb zircon geochronology with whole-rock and zircon rare earth element compositions ([REE]zirc), Ti-in-zircon thermometry (Tixln ) and 147Sm–143Nd geochronology for an individual subdivided ∼60 cm2 slab of Acasta banded gneiss comprising five separate lithologic components. Results were compared to other variably deformed granitoid-gneisses and plagioclase-hornblende rocks from elsewhere in the AGC. We show that different gneissic components carry distinct [Th/U]zirc vs. Tixln and [REE]zirc signatures correlative with different zircon U–Pb age populations and WR compositions, but not with 147Sm–143Nd isotope systematics. Modeled DWRzircon [REE] from lattice-strain theory reconciles only the ca. 3920 Ma zircons with the oldest component that also preserves strong positive Eu∗ anomalies. Magmas which gave rise to the somewhat older (inherited) ca. 4020 Ma AGC zircon age population formed at ∼IW (iron–wüstite) to <FMQ (fayalite–magnetite–quartz) oxygen fugacities. A ca. 3920 Ma emplacement age for the AGC is contemporaneous with bombardment of the inner solar system. Analytical bombardment simulations show that crustal re-working from the impact epoch potentially affected the precursors to the Acasta gneisses.
    Geochimica et Cosmochimica Acta 05/2014; 133:68–96. DOI:10.1016/j.gca.2014.02.019 · 4.33 Impact Factor
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    • "Subtle but resolvable differences in the 40 Ar– 39 Ar ages of melt breccias linked with lunar basins (Dalrymple and Ryder, 1996), and the recognition of discrete melt-forming impact events during the interval 3.8–4.0 Ga (Norman et al., 2006), support the concept of a late heavy bombardment , but whether this represents a short, sharp spike in the impact flux or a longer-lived epoch of basin formation is an open question with significant implications for solar system dynamics (Gomes et al., 2005), early planetary environments (Abramov and Mojzsis, 2009), and biological evolution (Chyba and Sagan, 1992; Farmer, 2000; Ryder, 2002; Marty and Meibom, 2007). The absence of crystalline impact melt rocks with ages older than 4.0 Ga has been cited as a key piece of evidence favoring a late cataclysm (Ryder, 2002). "
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    ABSTRACT: A sharp rise in the flux of asteroid-size bodies traversing the inner Solar System at 3.9 Ga has become a central tenet of recent models describing planetary dynamics and the potential habitability of early terrestrial environments. The prevalence of ∼3.9 Ga∼3.9 Ga crystallization ages for lunar impact-melt breccias and U–Pb isotopic compositions of lunar crustal rocks provide the primary evidence for a short-lived, cataclysmic episode of late heavy bombardment at that time. Here we report U–Pb isotopic compositions of zirconolite and apatite in coarse-grained lunar melt rock 67955, measured by ion microprobe, that date a basin-scale impact melting event on the Moon at 4.22±0.01 Ga4.22±0.01 Ga followed by entrainment within lower grade ejecta from a younger basin approximately 300 million yr later. Significant impacts prior to 3.9 Ga are also recorded by lunar zircons although the magnitudes of those events are difficult to establish. Other isotopic evidence such as 40Ar–39Ar ages of granulitic lunar breccias, regolith fragments, and clasts extracted from fragmental breccias, and Re–Os isotopic compositions of lunar metal is also suggestive of impact-related thermal events in the lunar crust during the period 4.1–4.3 Ga. We conclude that numerous large impactors hit the Moon prior to the canonical 3.9 Ga cataclysm, that some of those pre-cataclysm impacts were similar in size to the younger lunar basins, and that the oldest preserved lunar basins are likely to be significantly older than 3.9 Ga. This provides sample-based support for dynamical models capable of producing older basins on the Moon and discrete populations of impactors. An extended period of basin formation implies a less intense cataclysm at 3.9 Ga, and therefore a better opportunity for preservation of early habitable niches and Hadean crust on the Earth. A diminished cataclysm at 3.9 Ga suggests that the similarity in the age of the oldest terrestrial continental crust with the canonical lunar cataclysm is likely to be coincidental with no genetic significance.
    Earth and Planetary Science Letters 02/2014; 388:387–398. DOI:10.1016/j.epsl.2013.11.040 · 4.73 Impact Factor
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    • "Crater lakes, however, if fed by an active hydrothermal system, may have lived longer, but this activity still requires the presence of underground water (liquid or ice). Observations on Earth (Osinski et al., 2005) and numerical modeling (e.g., Abramov and Kring, 2005; Schwenzer and Kring, 2009) have shown that a crater-forming impact can result in the creation of a longlasting hydrothermal system when ice is present in the crust. For example, a 130 km large crater could sustain an active hydrothermal system for up to 2 million years (Schwenzer and Kring, 2009), that is, long enough for life to emerge. "
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    ABSTRACT: Abstract Extraterrestrial habitability is a complex notion. We briefly review what is known about the origin of life on Earth, that is, life based on carbon chemistry and water. We then discuss habitable conditions (past and present) for established life and for the survival of microorganisms. Based on these elements, we propose to use the term habitable only for conditions necessary for the origin of life, the proliferation of life, and the survival of life. Not covered by this term would be conditions necessary for prebiotic chemistry and conditions that would allow the recognition of extinct or hibernating life. Finally, we apply this concept to the potential emergence of life on Mars where suitable conditions for life to start, proliferate, and survive have been heterogeneous throughout its history. These considerations have a profound impact on the nature and distribution of eventual traces of martian life, or any precursor, and must therefore inform our search-for-life strategies. Key Words: Mars-Microbial life-Punctuated habitability. Astrobiology 13, xxx-xxx.
    Astrobiology 09/2013; 13(9). DOI:10.1089/ast.2013.1000 · 2.59 Impact Factor
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