Impact Generated Habitat
Overview: Meteorite impacts are a dominant geological process within our Solar System and can have devastating effects on biology, such as with the Chicxulub impact at 65 Ma. Though initially detrimental, however, these events can actually create habitats for life.
There are four types of impact generated habitats:
2) Surface endolithic
4) Post-Impact crater lakes
Briefly, the shockwave generated by a ballistic impact (which frequently results in the complete vaporization of the bolide), causes large-scale and micro-scale changes to the target that can be beneficial for life. The shockwave acts to disrupt the subsurface on a large scale and increases the available surface area by "brecciating" the target lithology. On a micron scale, the heat and pressure released through the impact cause melting and vaporization of minerals within the target rocks, which increases the porosity of these rocks. It's important here to understand that not all rocks respond the same way to the pressure wave: a lot of work has been done to characterize the differences between how sandstones (5% initial porosity) respond to the pressure wave (pore spaces close >35 GPa), and how crystalline rocks such as gneisses (0% initial porosity) respond, where porosity can increase to as much as 60-70%. This creates a lot of available surface area for microorganisms to colonize.
Why do microorganisms colonize rocks? Rocks are great habitats if you're a unicellular organism, this is because the rock provides a more temperature stable environment, is able to shield UV radiation, and can act as a catchment for water and air blown nutrients. In harsh environments such as polar deserts, the majority of surface microbial colonization occurs in (and underneath) rocks.
Beyond creating more surface area for microbes, impact events can generate transient hydrothermal systems, and if the crater walls are not breached, can host impact crater lakes once temperatures in the crater diminish to pre-impact levels. The impact-generated hydrothermal systems are hugely important for microorganisms, as these systems provide a source of heat, energy and nutrients. There is evidence for post-impact hydrothermal systems in several locations on Earth, such as Haughton Impact Structure, Ries Crater, Kardla Impact Structure and Lonar Crater, to name a few. Today, impact lakes can be found around the world, and are rich ecosystems.
Cockell, C. S., & Lee, P. (2002). The biology of impact craters—a review. Biological Reviews, 77(3), 279-310.
Osinski, G. R., Cockell, C. S., Pontefract, A., & Sapers, H. M. (2020). The Role of Meteorite Impacts in the Origin of Life. Astrobiology, 20(9), 1121-1149.
Pontefract, A., Osinski, G. R., Cockell, C. S., Moore, C. A., Moores, J. E., & Southam, G. (2014). Impact-generated endolithic habitat within crystalline rocks of the Haughton Impact Structure, Devon Island, Canada. Astrobiology, 14(6), 522-533.
Field Sites: Haughton Impact Structure
Overview: The Haughton impact structure is a 31 Ma complex crater, located on the northwestern region of Devon Island, Nunavut, in the Canadian High Arctic archipelago at 75°08’N, 87°51’W, and represents one of the best preserved impact craters in the world. The target rocks are almost entirely sedimentary, comprised of carbonates, with lesser amounts of evaporites, sandstone and shale, overlaying gneisses of the Precambrian basement of the Canadian Shield. Haughton has an apparent diameter of ~23 km, with a final crater rim estimate of 16 km in diameter.
The most identifiable feature of the impact structure is the pale-grey crater-fill (clast-rich impact melt rocks) deposits, which are found in multiple locations throughout the centre of the structure. Another important feature of the structure is its hydrothermal deposits, seen in the form of hydrothermal vugs, as well as deposits in the form of pyrite, marcasite and selenite. Finally, lacustrine deposits comprising the Haughton Formation are present in and around the centre of the crater, which represent the transient presence of a lake during the Neogene several Myr after the crater formed. These sediments contain fossilized pollen grains, plants and vertebrate skeletons, and represent a late stage in the biological succession of the crater.