78 million years ago, a 1.6 km asteroid slammed into what is now Finland, creating a crater 23 km (14 mi) wide and 750 km deep. The catastrophic impact created a fractured hydrothermal system in the shattered bedrock under the crater. There’s evidence from other impact structures that in the aftermath of a collision, life colonized the shattered rock and heated water that flowed through it. But determining when the colonization happened is challenging.
New research shows for the first time exactly when that colonization happened. A team of researchers has zeroed in on the date that microbial life populated the hydrothermal system under the 78 million year old Lappajärvi impact structure.
Their research is titled “Deep microbial colonization during impact-generated hydrothermal circulation at the Lappajärvi impact structure, Finland” and is published in Nature Communications. Jacob Gustafsson, a PhD student at Linnaeus University in Sweden, is the first author.
“This is incredibly exciting research as it connects the dots for the first time.” – Dr. Gordon Osinski, Western University, Canada.
“Deeply fractured rocks of meteorite impact structures have been hypothesized as hot spots for microbial colonization on Earth and other planetary bodies,” the authors write. “Biosignatures of such colonization are rare, however, and most importantly, direct geochronological evidence linking the colonization to the impact-generated hydrothermal systems are completely lacking.”
Illustration of new research findings in the Lappajärvi crater, Finland, where traces of ancient life have been discovered in the crater’s fractures. The magnified section highlights the blue-marked fracture zones where microbial signatures have been identified. Image Credit: Henrik Drake, Gordon Osinski
The discovery is based on sulphite reduction. Some microbes employ an anaerobic respiratory process that uses sulfate to accept electrons rather than oxygen. It’s a fundamental process that contributes to Earth’s global sulfate and carbon cycles. Basically, microbes break down organic compounds as an energy source and reduce sulfate to hydrogen sulfide.
The researchers used powerful, cutting-edge isotopic biosignature analysis and radioisotopic dating to trace microbial sulfate reduction in minerals and fractures in the hydrothermal system under the crater.
“This is the first time we can directly link microbial activity to a meteorite impact using geochronological methods. It shows that such craters can serve as habitats for life long in the aftermath of the impact,” says Henrik Drake, a professor at Linnaeus University, Sweden, and senior author of the study.
“The first detected mineral precipitation at habitable temperatures for life (47.0 ± 7.1 °C) occurred at 73.6 ± 2.2 Ma and featured substantially 34S-depleted pyrite consistent with microbial sulfate reduction,” the authors explain in their research.
This figure shows some of the findings. The pyrite is of particular interest. The 34Sulfur-depleted pyrite is consistent with microbial sulfate reduction. It formed about five million years after the impact when the hydrothermal system had cooled to temperatures that were habitable for life. The calcite is another powerful biosignature, and it appeared 10 million years post-impact, indicating that microbes thrived here for millions of years. Image Credit: Gustafsson et al. 2025 NatComm
“What is most exciting is that we do not only see signs of life, but we can pinpoint exactly when it happened. This gives us a timeline for how life finds a way after a catastrophic event” says Jacob Gustafsson, PhD student at Linnaeus University and first author of the study.
More evidence of microbial colonization appears about 10 million years post-impact as the temperature continued to gradually decrease. Minerals precipitated into vugs, which is a geological term for cavities lined with mineral crystals. These minerals feature 13 Calcite, which forms in association with microbial sulfate reduction. It’s a powerful and convincing biosignature that strengthens the findings. At 10 million years post-impact, these minerals are further evidence that microbes thrived for a long time in the hydrothermal system.
Co-author Dr. Gordon Osinski, from Western University in Canada, said “This is incredibly exciting research as it connects the dots for the first time. Previously, we’ve found evidence that microbes colonized impact craters, but there has always been questions about when this occurred and if it was due to the impact event, or some other process millions of years later. Until now.”
These findings open a window into how life might get started on habitable worlds. Asteroids are known to carry the basic building blocks of life, including amino acids. It’s possible they not only spread these materials throughout solar systems and galaxies in accordance with panspermia, but that they also create a ready-made home for life to gain a foothold in. The research also shows how life can rebound after a catastrophic impact that could overwhelm a biosphere.
The researchers say that the microbial colonization of the Lappajärvi impact structure is an analog for the emergence of life on early Earth, and even on Mars. Their methods of analysis can be used to study the microbial colonization of other impact structures on Earth. Beyond that, they’re also applicable to any sample return missions from Mars or other bodies.
“These insights confirm the capacity of medium-sized (and large) meteorite impacts to generate long-lasting hydrothermal systems, enabling microbial colonization as the crater cools to ambient conditions, an effect that may have important implications for the emergence of life on Earth and beyond,” the authors conclude.