Evolution: Ancient Life Discovered Deep Below the Seafloor in Mantle Rocks

Scientists have uncovered evidence of ancient life deep below the seafloor. Researchers have uncovered evidence of microbial life from drilled rocks samples of the Earth's mantle.

"We were initially looking at how seawater interacts with mantle rocks, and how that process generates hydrogen," said Frieder Klein, lead author of the new study, in a news release. "But during our analysis of the rock samples, we discovered organic-rich inclusions that contained lipids, proteins and amino acids-the building blocks of life-mummified in the surrounding minerals."

The researchers focused on mantle rocks that were originally exposed to seawater about 125 million years ago when a large rift split the massive supercontinent known as Pangaea. This rift, which eventually evolved into the Atlantic Ocean, pulled mantle rocks from Earth's interior to the seafloor. These rocks had chemical reactions with the sweater that transformed the water into a hydrothermal fluid.

"The hydrothermal fluid likely had a high pH and was depleted in carbon and electron acceptors," said Klein. "These extreme chemical conditions can be challenging for microbes. However, the hydrothermal fluid contained hydrogen and methane and seawater contains dissolved carbon and electron acceptors. So when you mix the two in just the right proportions, you can have the ingredients to support life."

The researchers found that colonies of bacteria and archaea were feeding off the sweater-hydrothermal fluid mix and became engulfed in the minerals growing in the fractured rock. The rocks provided what ultimately turned out to be storage containers for these organisms, preserving their lipids and proteins for 100 million years.

"In the future, we'll be trying to learn more about these particular microorganisms and what the environmental conditions were in the mixing zone in that location," said Klein. "We also plan to go to different places where we think similar processes may have taken place, such as along the Newfoundland margin, and analyze samples to see if we find similar signatures. Broadening this research could provide additional insights about Earth's history and search for life in the solar system."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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