Even in this time of 7 billion human inhabitants, there are still frontiers being explored on Earth. One frontier is Earth’s deepest depths, which scientists are probing for signs of life. In late 2010, microbiologist Stephen Giovannoni and his research team discovered bacterial life deeper in the Earth’s crust than ever before, 1.4 kilometers below the sea floor in the North Atlantic. This discovery might have implications for life on other planets, such as Mars.
For four months, a research ship, part of the Integrated Ocean Drilling Program, drilled down into the rock below the ocean floor to the deepest layer of Earth’s crust. Rock samples from the drill cores revealed living organisms. Giovannoni said:
This expedition investigated microbial life in gabbros, which are rocks in the deep part of the ocean crust, and discovered bacteria there.
How can bacteria, or any form of life, survive in rock so deep underground? Dr. Giovannoni explained that cracks in the ocean floor allow seawater and microbes to circulate through the Earth’s crust, bringing nutrients and other ingredients necessary for life.
These rocks are highly fractured. So the ocean actually circulates through the Earth’s crust at quite a high rate. So there are what are called hydrothermal fluids circulating through all these deep crustal rocks. And it’s wet down there, wet and warm.
He said his team wasn’t surprised to find organisms so deep beneath the ocean floor. They already knew that temperatures there were right for life and that there was water there.
The big surprise was the type of bacteria we found. They weren’t the same ones that were found in the basalts above. The organisms we found down there were normally associated with degrading hydrocarbons. Here’s what that means. Other scientists working in a nearby and very exciting area, called the Lost City Hydrothermal Vent, have reported that hydrocarbons in this region are being formed abiotically [from non-living chemical and physical factors in the environment]. That means, essentially, that carbon and hydrogen molecules are being made from carbon dioxide and hydrogen, in interactions between water and rock. These interactions are producing organic matter.
Organic matter in the part of the biosphere we’re used to all comes from photosynthesis. So it strongly appears that in this region of the Earth’s crust, at least, you’ve got abiotic synthesis of organic matter occurring, and that the microbial community we encountered is using that material as a source of nutrients for growth.
Giovannoni said this finding has many implications. For one thing, he said, it means that this community of microorganisms – far below the sea floor – might be subsisting on materials that are not derived from photosynthesis at the surface.
So they might be truly independent of the surface biosphere.
He said the discovery might also have implications for understanding what life might be like on other planets.
The planet that everybody is most interested in is Mars, because it’s known that there’s water on Mars. And it’s known that Mars is producing methane. And it’s a bit of a mystery of where that methane comes from. So one possibility is that it’s being produced by abiotic processes like this. And there’s always the possibility that there might be life on Mars. There’s no direct proof of that at this time. Enough is known about Mars to postulate that if there is life there, it’s probably some sort of subterranean life, occurring in rocks very much like the rocks that we were investigating in the North Atlantic.
Dr. Giovannoni said he believes scientists are motivated to look for life deep within the Earth for several reasons.
One is, these rocks certainly are similar to the kinds of rocks found on planets like Mars. And so one wonders whether similar processes could be, whether you could find out about what’s happening in the deep Earth sub-surface and whether similar processes might be happening elsewhere in the solar system.
Secondly, he said, learning about life below the sea floor in the North Atlantic might help shed light on how the climate and chemistry of our own planet formed and evolved. He said the interaction of seawater with rocks in Earth’s crust is a very important long-term process that has transformed the chemistry of seawater and continues to alter seawater chemistry.
And finally, he said, people are simply curious about the diversity of life on Earth.
There’s the feeling that we might discover new things about how diverse life is and how it’s able to harvest forms of energy that are unusual by going to these unusual, extreme environments.
Giovannoni said that there are no current plans to return to the area, but he’s hopeful that his team will eventually be able to drill deeper, past the crust, into the mantle, and perhaps find life there too.