Seventy-eight million years ago, a 1.6-kilometer asteroid slammed into what is now Finland, blasting out a 23-kilometer-wide crater and shattering the bedrock beneath. The catastrophic impact set off a long-lived hydrothermal system of hot, fractured rock. Flowing water created conditions thought to be prime real estate for microbial life, where microbes could thrive.
Now, researchers have shown exactly when life took hold. In a groundbreaking study published in Nature Communications, scientists from Linnaeus University in Sweden and collaborators used cutting-edge geochronological methods to directly link microbial activity to the Lappajärvi impact structure.
“This is incredibly exciting research as it connects the dots for the first time,” said Dr. Gordon Osinski of Western University, Canada, a co-author on the study.
Colonization in the wake of disaster
The team analyzed isotopic biosignatures and radioisotopic dating of minerals in the crater’s hydrothermal fractures. Their results point to microbial sulfate reduction—a process where microbes break down organic compounds and reduce sulfate to hydrogen sulfide—as the key evidence of life.
They found that the first mineral precipitation at habitable temperatures (around 47°C) occurred 73.6 million years ago, about 4.4 million years after the impact. The minerals showed sulfur isotope patterns that could only have been created by microbial activity.
“What is most exciting is that we do not only see signs of life. We can pinpoint exactly when it happened. This provides us with a timeline. It shows how life finds a way after a catastrophic event,” said Jacob Gustafsson, PhD student at Linnaeus University and first author of the paper.
Life lasted for millions of years
Evidence suggests microbial colonization continued for at least 10 million years as the crater gradually cooled. Minerals such as calcite, associated with microbial sulfate reduction, lined small cavities in the rock, further confirming long-term microbial activity.
“This is the first time we can directly link microbial activity to a meteorite impact. We used geochronological methods,” said Henrik Drake, senior author and professor at Linnaeus University. “It shows that such craters can serve as habitats for life long in the aftermath of the impact.”
Lessons for early Earth—and Mars
The findings carry implications far beyond Finland. Impact craters may have played a key role in supporting early microbial life on Earth, providing long-lasting, energy-rich environments in the wake of planetary bombardment.
Asteroids are known to deliver organic building blocks like amino acids. When combined with hydrothermal systems, they may provide the dual ingredients for life: raw materials and a habitable environment.
“This work shows how medium-sized impacts can create microbial refuges that last millions of years,” the authors write. “It has direct relevance for understanding how life began on Earth and whether similar processes could occur on Mars or other worlds.”
The team’s methods could also be applied to future sample return missions from Mars. They can help determine whether microbial colonization ever took place in Martian craters.
