This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study reveals that microbial life deep within Earth has persisted and repeatedly flourished through hundreds of millions of years of mountain-building and erosion. By analyzing minerals, fluids and gases from a 2.3-kilometer-deep (1.4-mile-deep) borehole in central Sweden, researchers have uncovered episodic bursts of methane-producing life linked to major geological events that shaped Scandinavia.
The paper is published in the journal Communications Earth & Environment. The deep continental subsurface is one of Earth's least explored ecosystems. Yet it hosts microbial communities capable of ancient metabolisms such as methanogenesis—the production of methane by microorganisms.
Now, an international research team led by scientists at Linnaeus University has reconstructed an unprecedented long-term history of these deep biosphere processes. The researchers analyzed fracture-filling calcite minerals from the COSC‑2 drill core, drilled west of Östersund in central Sweden. The borehole extends more than 2,300 meters (1.4 miles) into the bedrock and passes through several geological layers formed at different times in Earth's history.
The results revealed exceptionally high carbon isotope values in the calcite. Such signatures are a hallmark of microbial methanogenesis, in which microbes preferentially use lighter carbon isotopes, leaving behind a strongly enriched carbon reservoir. "These are some of the clearest mineral-scale fingerprints of deep microbial methane production that we've seen.
They show that microbial communities have left a chemical archive of their activity deep in the crust," says Henrik Drake, professor at Linnaeus University and senior researcher on the study. By dating the minerals using high-precision U–Pb dating, the team determined when episodes of methane production occurred. Rather than a single event, the results revealed multiple distinct episodes of microbial activity spanning from approximately 378 million years ago to as recently as 1.8 million years ago.
"This tells us that the deep biosphere is not static. Instead, it responds to geological processes over vast timescales, turning on and off as conditions shift," says Femke van Dam, researcher at Linnaeus University and lead author of the study. The borehole intersects rocks that were once part of the Caledonian mountain range, an ancient mountain belt that stretched across Scandinavia but has worn down over hundreds of millions of years.
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