The origin and emergence of life under impact bombardment

Abstract

Craters formed by asteroids and comets offer a number of possibilities as sites for prebiotic chemistry, and they invite a literal application of Darwin's 'warm little pond'. Some of these attributes, such as prolonged circulation of heated water, are found in deep-ocean hydrothermal vent systems, previously proposed as sites for prebiotic chemistry. However, impact craters host important characteristics in a single location, which include the formation of diverse metal sulphides, clays and zeolites as secondary hydrothermal minerals (which can act as templates or catalysts for prebiotic syntheses), fracturing of rock during impact (creating a large surface area for reactions), the delivery of iron in the case of the impact of iron-containing meteorites (which might itself act as a substrate for prebiotic reactions), diverse impact energies resulting in different rates of hydrothermal cooling and thus organic syntheses, and the indiscriminate nature of impacts into every available lithologygenerating large numbers of 'experiments' in the origin of life. Following the evolution of life, craters provide cryptoendolithic and chasmoendolithic habitats, particularly in non-sedimentary lithologies, where limited pore space would otherwise restrict colonization. In impact melt sheets, shattered, mixed rocks ultimately provided diverse geochemical gradients, which in present-day craters support the growth of microbial communities.

Physical conditions on the early Earth

“…The second analogy with the Earth has to do with hydrothermal environments generated by large impact craters, which may have produced localized habitable hydrothermal systems on the early Earth and Mars in locations where volcanic hydrothermal systems did not exist (Cockell 2006). The equivalent probably has existed on Titan as well.…”

“…Smaller impactors-of order 100 km or less in size-while destroying the organic inventory of particular local areas, might have created post-impact environments that were particularly favourable for the origin of life, by creating large surface areas for reaction, introducing important trace minerals and synthesizing mineral surfaces appropriate for templatedriven chemistry (Cockell 2006). Furthermore, oblique impacts of smaller (1-10 km scale) impactors leave a relatively lightly shocked or unshocked region in the wake of the impact plume, preserving or only lightly altering organic deposits (Artemieva & Lunine 2005).…”

Environmental regulation in a network of simulated microbial ecosystems

“…Our model may be particularly relevant to the early Earth. After its origin, life may have been distributed in different ''ponds'' [e.g., abundant meteorite craters (30)]. Exchange of organisms and material between these ponds could occur through airborne transport or f looding events.…”

Catalysis in the Primordial World

“…135 Hyperthermophiles 136 were in turn found near the underwater hydrothermal vents at Midoceanic ridges rich in dissolved hydrogen sulfide, 137,138 the possible geological habitat of pioneer organisms. 126 (Other habitats might also be magnesium-rich komatiite lava deposits 139 and hydrothermal systems developed as a consequence of asteroid impacts on early Earth, 140 but in our opinion, such events were rare.) Hyperthermophiles had possibly evolved from pioneer organisms, and were later adapted to "milder" surface conditions.…”