An international group of scientists is closing in on the end of a 10-year study that has uncovered secrets of "deep life," a stunningly diverse population of microscopic organisms miles inside Earth's surface. Some of those organisms live off little other than the energy of surrounding rocks — and survive in temperatures hotter than boiling water.
Undertaken by some 1,000 scientists, the Deep Carbon Observatory (DCO) project aims "to understand the quantities, movements, forms and origins of carbon inside Earth," according to the website. Carbon is essential to life. The DCO estimates that the amount of carbon underneath the surface is hundreds of times more than all the carbon in humans.
"A decade ago, we had no idea that the rocks beneath our feet could be so vastly inhabited," Isabelle Daniel, a geobiologist from the University of Lyon 1 in France, said in a press statement. "Experimental investigations told us that microbes could potentially survive to great depth; at that time, we had no evidence, and this has become real 10 years later. This is simply fascinating and will surely foster enthusiasm to look for the biotic-abiotic fringe on Earth and elsewhere."
During the course of their studies, scientists drilled more than 1.5 miles (2.5 kilometers) into the sea floor, captured samples from mines and boreholes from depths more than 3.1 miles (5 kilometers), and took the data from these hundreds of sites to get an idea of what an ecosystem in subterranean rock within the surface of Earth looks like. The biosphere they've uncovered is thought to be twice the volume of all the oceans.
This living world in the rock underneath our world consists of three types of life: two microbes that dominate the underground world — archaea (microbes with no membrane-bound nucleus) and eukarya (microbes or multicellular organisms with cells that contain a nucleus as well as membrane-bound structures within a cell) — and bacteria. Scientists report millions of distinct types of life there, most as-yet discovered or named.
This new world underneath the surface may even be more diverse than life on Earth. Yet these microbes are nothing like life on Earth. Many have life cycles measured in geologic terms.
The implications of these findings is wide-ranging. These organisms show they can live and thrive in highly pressurized environments, with few nutrients and in temperatures that would kill organisms on the surface. They may now give us clues about the possibility of life in other areas. Or on other planets.
"I think it's probably reasonable to assume that the subsurface of other planets and their moons are habitable," Rick Colwell, a microbiologist from Oregon State University, told the BBC, "especially since we've seen here on Earth that organisms can function far away from sunlight using the energy provided directly from the rocks deep underground."
For all the DCO has discovered, of course, many questions still remain. How does this "deep life" spread through rock? Is this where life began on Earth, percolating up toward the sun? Or is it the other way around? Without nutrients, where do these life forms get their energy?
The studies present a whole new world of questions, for a whole new world underneath the surface of the planet.