Microbes may have lived underground for more than a billion years

Microbes may have lived underground for more than a billion years

Microorganism-related calcite from a deep quarry in Swedish granite. This kind of mineral-related biosignatures were used as part of this new study to look for old habitable conditions in depth. Credit: Henrik Drake

A study using the thermal history and biosignatures from the top few kilometers of some of the oldest rocks on Earth places limits on the evolutionary history of microbes in the deep biosphere. A new study, published in PNAS, Proceedings of the National Academy of Sciences, shows that the rocks were uninhabitable for a large part of their lifetime, with the longest period of habitability not extending much over 1 billion years, and usually much shorter. Understanding the history of the deep biosphere can provide insight into the evolution of life on Earth.

The deep, dark and anoxic fracture systems of the Precambrian cratons on Earth are home to microorganisms that derive their energy from the consumption of gases, nutrients in liquids and sparingly available organic carbon. Most current estimates show that this deep biosphere hosts the majority of microbial life on Earth and about 10-20% of all terrestrial biomass.

These ecosystems host microbial lineages that are of interest in understanding the origin and evolution of life on our planet, but remain the least explored and understood ecosystems on Earth. Understanding the history of these microbial communities requires assessment of the complex evolution of habitable conditions, but such an assessment has not been presented until now.

In a new study, Henrik Drake, associate professor at Linnaeus University, Sweden, teamed up with Professor Peter Reiners of the University of Arizona to present the first thermochronological perspective on the habitability of Earth’s Precambrian cratons over time. The study suggests that the longest record of continuous habitability to the present does not extend much beyond 1 billion years.

Henrik Drake explains the discoveries:

“In this study, we wanted to combine the registration of signatures of deep ancient life found in craton fracture systems with the latest advances in medium and low temperature thermochronology. The cratonic rocks were formed billions of years ago, deep in the crust, at. “temperatures were too high for any life. It was only much later, after erosion, that the currently exposed rocks reached levels in the crust where the temperature was habitable.”

Microbes may have lived underground for more than a billion years

Dr. Henrik Drake. Credit: Ivan Pidchenko

Assessing when these rocky environments became habitable, and in some cases, when they may have been buried and sterilized again, provides new insight into the evolutionary aspect of the deep biosphere. This is especially important because the microbes in depth use the same metabolism that is expected for the earliest metabolism on Earth. There are also recent reports of exciting long stays for deep liquids in some of the Earth’s cratons, further suggesting the importance of understanding when these systems have maintained active ecosystems.

“By combining thermochronological results from several different radioisotopic dating systems, we can reconstruct their thermal histories through the ups and downs of burial and erosion over time. This approach gives us context to prospect and interpret the little explored geological record of the deep biosphere of Earth. kratoner. ”

The researchers were able to successfully correlate their fossil records of deep ancient life in Scandinavian cratonic rocks with habitable periods from the thermochronological framework.

Henrik Drake summarizes the results:

“This made us sure we could do the other way too – using thermochronology to point to candidate areas for the oldest records of subterranean microorganisms on Earth. Eastern Finland, Greenland and perhaps parts of the Canadian shield look particularly interesting with habitable conditions that stretch back a billion years or more. These are obvious targets for further studies of deep microbial evolution. ”

Deep bedrock mineral veins are microbial cemeteries

More information:
The results are presented in the article “Thermochronological perspectives on the deep time evolution of the deep biosphere”, Proceedings of the National Academy of Sciences, published November 1, 2021. www.pnas.org/cgi/doi/10.1073/pnas.2109609118

Provided by Linnaeus University

Citation: Microbes may have lived underground for more than a billion years (2021, November 1) Retrieved November 2, 2021 from https://phys.org/news/2021-11-microbes-underground-billion-years.html

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