Fractured rocks of impact craters have been suggested to host deep microbial communities on Earth, and potentially other terrestrial planets, yet direct evidence remains elusive.
In a new study published in Nature Communications, a team of researchers shows that the largest impact crater in Europe, the Siljan impact structure, Sweden, has hosted long-term deep microbial activity.
Life thrives deep beneath our feet in a vast but underexplored environment coined the deep biosphere. Colonization of these 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.
At the scenic site of Siljan, in the heart of Sweden, an impressive impact structure of >50 km diameter formed almost 400 million years ago. Previous well-known drilling attempts for deep natural gas are now renewed, and from these newly retrieved drill cores, a team of researchers have found widespread evidence of deep ancient life.
Henrik Drake, of the Linnaeus University, Sweden, and lead author of the study, explains the discovery:
“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.”
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