IMPACT CRATERS AS HABITATS FOR LIFE ON EARLY EARTH AND MARS

Despite the controversy over when exactly life appeared on Earth, it is likely that it did so during one of the harshest, most inhospitable times in Earth history: the Late Heavy Bombardment Period ~4.0–3.8 Ga. During this time, asteroid and comet impacts were ~10–20 times as frequent as they are at the present day. The deleterious effects of impact events have received a great deal of attention recently, prompted in a large part by the discovery of the Chicxulub impact structure, Mexico, and its link to the Cretaceous–Tertiary mass extinction event. However, a growing body of evidence suggests that impact events also have beneficial effects. Based on our multi-year studies of the Haughton impact structure, Canadian High Arctic, several other terrestrial impact sites, and a review of the existing literature, we will discuss the potential habitats associated with impact craters that may have been important on the early Earth and, by analogy, on other planets such as Mars. In summary, impact events generate heat sources capable of sustaining hydrothermal systems which could provide habitats for thermophilic and hyperthermophilic micro-organisms. This may have important astrobiological implications because hydrothermal systems in general might have provided habitats or ‘cradles' for the origin and evolution of early life on Earth, and possibly other planets such as Mars (e.g., Farmer 2000). Following this initial phase of hydrothermal succession, several other habitats will become important, including: (1) Impact-processed crystalline rocks, which have increased porosity and translucence compared to unshocked materials, improving microbial colonization (Cockell et al., 2002). (2) Impact crater lakes, which form protected sedimentary basins that can provide improved environments for sustaining communities of primitive phototrophs and increase the preservation potential of fossils and organic material. Other potential impact crater habitats will be also discussed.

References: Cockell C. S., Lee P., Osinski G. R., Horneck G., and Broady P. 2002. Impact-induced formation of microbial endolithic habitats. Meteoritics & Planetary Science 37:1287–1298 . Farmer J. D. 2000. Hydrothermal systems: Doorways to early biosphere evolution. GSA Today 10:7:1–9.