You would need a microscope to see this subterranean biosphere, however.
It is made up mostly of microbes, such as bacteria and their evolutionary cousins, the archaea.
Nonetheless, it represents a lot of carbon - about 15 to 23 billion tonnes of it. That is hundreds of times more carbon than is woven into all the humans on the planet.
"Something like 70% of the total number of microbes on Earth are below our feet," said Karen Lloyd from the University of Tennessee at Knoxville, US.
"So, this changes our perception of where we find life on Earth, from mostly on the surface in things like trees and whales and dolphins, to most of it actually being underground," she told BBC News.
Prof Lloyd is part of the Deep Carbon Observatory (DCO) project, a near-decade long effort to identify how the ubiquitous element is cycled through the Earth system. The consortium is reporting its latest discoveries here at the American Geophysical Union (AGU) annual Fall Meeting in Washington DC.
BBC
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