Microorganisms discovered under seabed

Scientists have discovered life in the deepest parts of the rock floor under the oceans - tiny microorganisms that live in the 'lower oceanic crust'. Melanie Jans-Singh reports...

Melanie - Over the last decades, researchers have looked for signs of life underground, in gold mines and in the seafloor. They’ve focused mostly on life in the first layer of the seafloor, which consists of sediments, and that’s mud mixed with dead fish and other microorganisms containing carbon. Below the mud is the rocky ocean crust. And the lower crust has not been explored much because it's typically 4-8 km deep. 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.

Ginny - We really didn't know what to expect because it seems like such an inhospitable environment.

Melanie - That's Ginny Edgcomb, from the Woods Hole Oceanographic Institution.

Ginny - But there had been a study previously, that had found signatures of life in gabbro samples from another location. And so we were optimistic that we might find something and we thought if we did, we'd probably find signs of life around cracks and fissures in the rock where fluids might be able to deliver carbon and energy sources to microbes living down there.

Melanie - How did you manage to get samples from under the sea floor like that?

Ginny - This kind of work is made possible through ocean drilling and requires a special drill ship that can hold a position over a spot that you want to drill into the sea floor on. And, and we spent two months, drilling down through the lower crust at this one location and every 10 meters of advancement a sample of the rock would come up to the drill ship and people would be able to quickly process it, and we could take samples for microbiology.

Melanie - How did you make sure that nothing was being contaminated by the environment around you?

Ginny - Since drilling requires us to pump fluid down to the drill bit to keep it cool while it's drilling, we had to be really careful that we removed all traces of that fluid before we collected samples for analysis. We did this in a couple of different ways. We ran a chemical along with the seawater and mud that the ship pumps down to the drill bit. We put a chemical in there that we would be able to detect in the laboratory, and we made sure that we couldn't detect any more traces of that chemical before we collected samples for analysis.

Melanie - When analysing in the lab they also checked that they were not contaminating through the lab equipment or the handling process, and took many steps to control everything, sometimes throwing away possibly good data. It was worth it though! They found that microorganisms deep under the seafloor were alive because they had genes to do things like dividing, which must mean they have enough food to live on. I asked Ginny how they could survive there?

Ginny - Organisms that live so far under the sea floor have to survive by being able to store carbon. When they see it, they can store it. We think in the form of a molecule that is kind of like storing fat would be for humans. But it's not fat. They can store it and keep it for a rainy day. They can also recycle different forms of carbon internally, which is something not all organisms do or have to do because they live in environments where they have plenty of carbon to access. So in the deep seafloor, and below the seafloor, many organisms are probably in a state of suspended animation. You know, they're just eking out a living.

Melanie - Even if the cells down there are just surviving, they're still consuming carbon. So now we know to take these organisms into account when calculating the world's carbon budgets.

Ginny - We are expanding our idea of what the habitable portion of Earth's biosphere is. 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.