Life discovered deep in the ocean floor

30 March 2020

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Light shines on sea floor

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Scientists have found life in the deepest rock layers under the ocean. The results extend what we regard as the habitable space on Earth...

Microorganisms that survive on meagre sources of carbon and energy have been found in fissures and cracks in the rocks 4 to 8 km below the seabed.

Even though these organisms are found rarely and are relatively metabolically inactive, they contribute significantly to the world’s carbon budget, and how carbon is sequestered and recycled to the surface. 

“We’re expanding our idea of what the habitable portion of Earth's biosphere is,” explains Ginny Edgcomb from Woods Hole Oceanographic Institution in the US, who led this study and discovered the ocean-floor dwelling microbes. “So it’s not just what you see above land and in the oceans, and it’s not just the muddy ocean sediments, it’s not just the basalts of the upper ocean crust,  but it now includes at least some portion of the lower ocean crust.”

The scientists confirmed the cells in the rock samples were living organisms because they contained genes for processes like cell division, and contained molecules for storing carbon, enabling them to survive for long periods of time without fresh food supplies.

Owing to its extreme depth, the lower crust, typically 4-8 km down beneath the rocky upper crust and the muddy sedimentary layer of the seafloor, has barely been explored. “But there are parts of the world where this lower crust is exposed, like in Atlantis bank in the middle of the Indian ocean where this expedition took place,” says Edgcomb. 

Here, the lower crust was just 700m down, enabling the team to extract samples using a special drilling vessel.

Every 10m, they would extract a core of rock, and then send the drill back down again. Samples of rock were taken from these cores and the geology and microbiology analysed.

Essential to the discovery of a new lifeform is to avoid contamination of the samples, in order to make sure that the detected microorganisms do not already exist elsewhere. The scientists mixed a tracer with a known chemical composition in the drilling fluid so they could be certain that the samples they were collecting had not been contaminated by the drilling process.

“We were extremely cautious,” says Edgcomb, “to make sure the sample was not contaminated by anything in the lab”. They even threw away “bits that would have probably been good” in order to guarantee that the sample only contained content from the lower ocean crust.

The results show that life is even better at eeking out an existence under even extreme conditions than we had anticipated. This means that the likelihood of finding life in equivalently extreme conditions on other worlds is correspondingly higher too...

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