New research has hinted how the remnants of terrestrial impact craters could have hosted microbial communities on Earth. A new study published in Nature Communications indicates the Siljan impact crater in Sweden – Europe’s largest impact crater – possibly hosted long-term deep microbial activity. Life burrowed deep beneath the surface surprisingly thrives in an enormous but under-explored environment, dubbed the deep biosphere. 

Colonisation of these extreme subterranean environments on Earth and possibly on exoplanets. And such life may possibly have been seeded by meteorite impacts. 

These violent events provide both space for microbial communities due to intense fracturing, while blistering heat drives fluid circulation favourable for underground ecosystems. 

Such systems may have served as unexpected havens for life, with considerable astrobiological implications for otherwise geologically dead planets. 

Astrobiology is an interdisciplinary scientific field concerned with the origins, early evolution, distribution, and future of life in the universe. 

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“We examined the intensively fractured rock at significant depth in the crater and noted tiny crystals of calcium carbonate and sulphide in the fractures. 

“When we analysed the chemical composition within these crystals it became clear to us that they formed following microbial activity. 

“Specifically, the relative abundance of different isotopes of carbon and sulphur within these minerals tells us that microorganisms that produce and consume the greenhouse gas methane have been present, and also microbes that reduce sulphate into sulphide.“ 

The British Geological Survey’s Dr Nick Roberts, co-author of the study, revealed how the timescale of the microbial activity was estimated: 

He said: “We applied newly developed radioisotopic dating techniques to the tiny calcite crystals formed following microbial methane cycling, and could determine they formed in the interval 80 to 22 million years ago. 

“This marks long-term ancient microbial activity in the impact crater, but also the microbes lived up to 300 million years after the impact.” 

Dr Drake thinks multiple methods are now required to understand the link between the impact and the colonisation of life. 

He said: “At Siljan we see that the crater is colonised but that it has mainly occurred when conditions, such as temperature, became more favourable than at the impact event. 

“The impact structure itself, with a ring zone of down-faulted Paleozoic sediments, has been optimal for deep colonisation, because organics and hydrocarbons from shales have migrated throughout the fractured crater and have acted as energy sources for the deep microbial communities.” 

Dr Christine Heim, of University of Göttingen, Germany, another co-author of the groundbreaking meteor crater investigation believes the study has “astrobiological implications”. 

She said: “The preserved organic molecules that we could detect within the minerals give us additional evidence both for microbial activity in the crater, as we find molecules specific to certain microorganisms, but also for microbial biodegradation of shale-derived hydrocarbons, ultimately leading to production of secondary microbial methane at depth.” 

“Detailed understanding of microbial colonisation of impact craters has wide-ranging astrobiological implications.“ 

Dr Magnus Ivarsson, Swedish Museum of Natural History, and co-author of the study, added: “The methodology that we present should be optimal to provide spatiotemporal constraints for ancient microbial methane formation and utilisation in other impact crater systems, such as the methane emitting craters on Mars.” 



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