Fans of astrobiology may be aware of the theory of panspermia – that objects such as meteorites may carry life from one planet to another. But there is another connection between meteorites and life: their impacts improve conditions for life in sub-surface environments. We spoke with Dr. Henrik Drake, a research scientist at Linnaeus University who studies this very phenomenon. He explains the research and its implications for astrobiology.
What is the relationship between impact craters and microbial life?
Colonization of deep environments – on Earth and potentially on other Earth-like planets – may have been sparked by meteorite impacts. Such violent events provide both space to microbial communities due to intense fracturing, and heat that drives fluid circulation favorable for deep ecosystems. Especially on planetary bodies that otherwise are geologically dead, such systems may have served as rare havens for life with considerable astrobiological implications.
How does your research affect our understanding of astrobiology?
We present evidence of long-term microbial life deep within fractured rock of the largest impact crater in Europe, the Siljan crater in Sweden. We find diagnostic microbial signatures (organic molecules and isotopes) within minerals in the crater and could establish when the minerals formed by using geochronological methods. This gives knowledge of when the impact crater was colonized and by what microorganisms. Our study shows that detailed multi-method investigations are needed to understand the link between the impact and the colonization. The methodology that we present should be optimal to provide spatiotemporal constraints for ancient microbial methane formation. It can also be used to understand other impact crater systems, such as the methane emitting craters on Mars.
How did you come to be focused on such an interesting area of study?
I have for a long time studied ancient and ongoing microbial activity deep within the crust, but earlier my focus was on potential sites for nuclear waste repositories. To be able to study the deep biosphere in bedrock, deep drillings or underground excavations are crucial (but rare). At the Siljan impact site, there are currently drilling campaigns for deep natural gases and I was lucky to get sampling access to these unique drill cores. Through our analyses we could establish that microbes have produced methane deep within the fractured rock of the crater, for up to 80 million years.