Researchers at the Deep Carbon Observatory say the diversity of the ecosystem below the Earth’s surface is twice the size of world’s oceans and bears comparison to the Amazon or the Galápagos Islands. Unlike those places, the underground environment is still largely pristine because people have yet to probe most of the subsurface. Despite extreme heat, no light, minuscule nutrition and intense pressure, scientists estimate this subterranean biosphere is teeming with between 15 billion and 23 billion tonnes of micro-organisms, hundreds of times the combined weight of every human on the planet.
The researchers said their discoveries were made possible by two technical advances: drills that can penetrate far deeper below the Earth’s crust, and improvements in microscopes that allow life to be detected at increasingly minute levels. The scientists have been trying to find a lower limit beyond which life cannot exist, but the deeper they dig the more life they find. There is a temperature maximum – currently 122 degrees Celsius – but the researchers believe this record will be broken if they keep exploring and developing more sophisticated instruments.
Associate professor at the University of Tennessee Karen Lloyd 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.” The team combines 1,200 scientists from 52 countries in disciplines ranging from geology and microbiology to chemistry and physics and a year prior to the conclusion of their ten-year study, they will present an amalgamation of findings to date before the American Geophysical Union’s annual meeting opens this week.
Ms. Lloyd added, “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.” Samples were taken from boreholes more than 5 kilometres deep and undersea drilling sites to construct models of the ecosystem and estimate how much living carbon it might contain. The results suggest 70 percent of Earth’s bacteria and archaea exist in the subsurface. One organism found 2.5 kilometers 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.
Rick Colwell, a microbial ecologist at Oregon State University, said the timescales of subterranean life were completely different, where 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,” he said.
Underworld biospheres vary depending on geology and geography. Their combined size is estimated to be more than 2 billion cubic kilometres, but this could be expanded further in the future.