Science Alert
Earth is not the home you think it is. Far below the scant surface spaces we inhabit, the planet is teeming with an incredibly vast and deep ‘dark biosphere’ of subterranean lifeforms that scientists are only just beginning to comprehend.
Hidden throughout this subsurface realm, some of the world’s deepest and oldest organisms thrive in places where life shouldn’t even exist, and in new research, scientists have quantified this ‘dark matter’ of the microbial world like never before.
There’s a good reason why the sampling remains in its early stages.
“Ten years ago, we had sampled only a few sites – the kinds of places we’d expect to find life,” explains microbiologist Karen Lloyd from the University of Tennessee at Knoxville.
“Now, thanks to ultra-deep sampling, we know we can find them pretty much everywhere, albeit the sampling has obviously reached only an infinitesimally tiny part of the deep biosphere.”
Above: Candidatus Desulforudis audaxviator (purple bacteria straddling orange carbon spheres) from under Mponeng gold mine in South Africa.
In a preview of results from an epic 10-year collaboration by over 1,000 scientists, Lloyd and fellow researchers with the Deep Carbon Observatory (DCO) estimate the deep biosphere – the zone of life under Earth’s surface – occupies a volume of between 2 to 2.3 billion cubic kilometres (0.48 to 0.55 billion cubic miles).
That’s almost twice the volume of all the world’s oceans – another enormous natural environment that lies largely unexplored by humans.
And just like the oceans, the deep biosphere is an abundant source of countless lifeforms – a population totalling some 15 to 23 billion tonnes of carbon mass (between 245 to 385 times greater than the equivalent mass of all humans on the surface).
The findings, representing numerous studies conducted at hundreds of sites around the world, are based on analyses of microbes extracted from sediment samples sourced 2.5 kilometres (1.6 miles) under the seafloor, and drilled from surface mines and boreholes more than 5 kilometres (3.1 miles) deep.
Hidden at these depths, two forms of microbes (bacteria and archaea) dominate the deep biosphere, and are estimated to make up 70 percent of all Earth’s bacteria and archaea.
As for how many kinds of organisms we’re talking about, nobody knows.
But the Deep Carbon Observatory scientists say millions of distinct types are waiting to be discovered and characterised with these techniques.