Have Researchers Really Found Life Within Earth's Mantle?

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An international team of scientists, having just returned from a 47-day-long expedition to the mid-Atlantic, have announced in a statement that they have found microbial life dwelling in mantle rocks. Despite several headlines declaring or implying that life has been found within the molten mantle itself, the reality is far less controversial.

The team was excavating samples from a deep, rocky region called the Atlantis Massif. It is situated on the western side of the Mid-Atlantic ridge, the fiery chasm from which new oceanic crust is born. This dome-shaped formation is unlike the basaltic rock typically found in the surrounding oceanic crust, in that it is made of green peridotite, a rock type found in the depths of the mantle.

The team, investigating how seawater interacts with crustal and mantle rocks, began drilling into the Massif, and it was within this formation that their discovery was made. “During the expedition, we were able to find evidence for microscopic ‘microbial’ life in shallow mantle rocks that have been brought near the seafloor,” expedition member Dr. Beth Orcutt, a senior research scientist at the Bigelow Laboratory for Ocean Sciences in Maine, told IFLScience.

However, despite reports to the contrary, the researchers are not saying this life originated in the mantle itself. Instead, they have simply found evidence of life in the mantle rocks within the seafloor, suggesting that the interaction of the rocks and the seawater may fuel life, even in the absence of sunlight.

Although the Massif once formed within the depths of the molten mantle, which even near the oceanic crust can reach temperatures of up to 900°C (1,650°F), it is no longer there; it has been exhumed to the seafloor long ago, and has since cooled down considerably. It now rises up 4,000 meters (2.5 miles) from the seafloor.

By chance, this complex now happens to be situated nearby the Lost City Hydrothermal Field, a series of hydrothermal vents that form when near-boiling seawater reacts with shallow mantle minerals. At both the vents and within the nearby geology, a process known as “serpentinization” occurs, which among other things produces microscopic holes or “pores” within the rock.

These carbonate growths form part of the Lost City Hydrothermal Field; primitive life can be found living on and within them. National Science Foundation

Within these pores, dissolved substances used by primitive life forms – including hydrogen and methane – are known to be concentrated. Some think that the nucleic acids that form RNA, a vital component within all living cells, has a good chance at forming in these pore spaces.

Indeed, life is found all across these vents, from more advanced shellfish to far more primitive bacteria. Even biofilms of archaea – single-celled microorganisms without a cell nucleus – are found using the methane and hydrogen within these serpentinite pores, oxidizing them to produce energy.

This research team, part of the International Ocean Discovery Program (IODP), may have found microbial life within the nearby exhumed Massif, but considering that microbial life is commonplace in the region, this shouldn’t come as a huge surprise. The rocks within the Massif are also serpentinite-rich, and also contain pore spaces full of hydrogen and methane.

“At this time, we do not know the identity of these microbial cells,” Orcutt added. Formal identification “will require more laboratory analyses over the coming months to years.” Going by what’s found in the nearby hydrothermal vent ecosystems, it is likely that they are either bacterial or from the archaea domain of life.

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