In a recent paper published in the journal Astrobiology, Gordon Osinski from the University of Western Ontario and colleagues lay out the case for why asteroid and cometary impacts are not always harbingers of death. In fact, they often create temporarily habitable conditions on a planet otherwise challenging for life. They may even have been instrumental in the origin of life on Earth.
The authors describe how impacts can create potential niches for life by generating hydrothermal vents and liquid water bodies, consistent with the two leading hypotheses for the rise of life on Earth: that it began at submarine hydrothermal vents or in “Darwin’s little pond,” possibly heated from the aftereffects of the impact. Impacts also generate potential living space in the subsurface by fracturing the planetary crust and producing clays that can act as catalyzers for chemical reactions.
Given that impacts were much more common in the first half-billion years of our planet’s history, it is likely they played a critical role in getting life going. Comets in particular would have provided a rich suite of organic compounds that would have served as the building blocks of life.
The authors suggest that impacts would have produced habitable conditions on planetary bodies inside and outside of our Solar System—even ones that may not have life today. They give Mars, the dwarf planet Ceres and Saturn’s moon Titan as examples. Titan is especially interesting in this regard, because it has a rich supply of organic compounds and an atmosphere even more substantial than Earth’s. Any large impact could have kept water liquid near the surface for a very long time.
On Mars, impacts would likely have increased the habitability of the subsurface. Ancient impact craters can therefore be considered prime sites to search for evidence of past and perhaps even current Martian life. A modern-day large impact crater might be even more revealing: It would melt any underground ice in the vicinity, and the newly formed crater would fill up with water and freeze over. Sampling that ice would give us a window to find out whether the otherwise hard-to-reach subsurface contains indigenous microbes.
I’m not sure Osinski can ever make the general public feel warmly about asteroid impacts, however. The image of dinosaurs (non-avian dinosaurs, that is) being killed off after the Chicxulub impact at the end of the Cretaceous period is too vivid in our collective mind. An impact nowadays would wreak unimaginable havoc on humanity and all of Earth’s biosphere. But he is correct that, at other times and on other worlds, meteorites might be life-starters instead of life-enders.