Many scientists believe that life exists deep beneath the Earth’s surface, not only changing what we know about life but also how we might look for life on alien planets. Now, scientists at the Deep Carbon Observatory have provided evidence on it. They reveal a rich ecosystem beneath our feet that is almost twice the size of all the world’s oceans.
Scientists discovered bacteria, archaea, and other microbes—some of them zombies—exist even in deepest known subsurface, and they’re weirder than their surface counterparts.
On the eve of the American Geophysical Union’s annual meeting, scientists reported several transformational discoveries, including how much and what kinds of life exist in the deep subsurface under the greatest extremes of pressure, temperature, and low energy and nutrient availability.
They also reported that life constitutes an immense amount of carbon deep within Earth’s subsurface is 245 to 385 times greater than the carbon mass of all humans on the surface.
Karen Lloyd, an associate professor at the University of Tennessee in Knoxville said, “It’s like finding a whole new reservoir of life on Earth. We are discovering new types of life all the time. So much of life is within the Earth rather than on top of it.”
Scientists took samples from boreholes more than 5km deep and undersea drilling sites to construct models of the ecosystem and estimate how much living carbon it might contain.
They found that 70% of Earth’s bacteria and archaea exist in the subsurface, including barbed Altiarchaeales that live in sulphuric springs and Geogemma barossii, a single-celled organism found at 121C hydrothermal vents at the bottom of the sea.
One organism found 2.5km below the surface has been buried for millions of years and may not rely at all on energy from the sun. Instead, the methanogen has found a way to create methane in this low energy environment, which it may not use to reproduce or divide but to replace or repair broken parts.
Lloyd said: “The strangest thing for me is that some organisms can exist for millennia. They are metabolically active but in stasis, with less energy than we thought possible of supporting life.”
Rick Colwell, a microbial ecologist at Oregon State University, said, “the timescales of subterranean life were completely different. Some microorganisms have been alive for thousands of years, barely moving except with shifts in the tectonic plates, earthquakes or eruptions.”
“We humans orientate towards relatively rapid processes – diurnal cycles based on the sun, or lunar cycles based on the moon – but these organisms are part of slow, persistent cycles on geological timescales.”
Scientists are now trying to discover a lower limit beyond which life can’t exist, however, the deeper they dig the more life they find. There is a temperature maximum – currently 122C – yet the scientists trust this record will be broken on the off chance that they continue investigating and growing increasingly sophisticated instruments.
Robert Hazen, a mineralogist at the Carnegie Institution for Science, said: “We must ask ourselves: if life on Earth can be this different from what experience has led us to expect, then what strangeness might await as we probe for life on other worlds?”