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An international team of scientists are completing a 10-year research project designed to test for life deep within the earth’s surface.

The ‘Deep Carbon Observatory’ project involved drilling deep into the seafloor and sampling microbes from mines and boreholes up to three miles underground. Results from the study have shown there is an astonishingly rich and diverse array of microorganisms living miles inside the earth’s surface, living in a habitat nearly twice the size of the oceans.

These microorganisms are surviving in extreme conditions including high temperatures, high pressures and lack of nutrients; yet despite these hostile conditions, scientists found this hidden world is home to 70 per cent of earth’s bacteria and their cousins the archaea.

The aim of the study was to investigate the amount and different forms of carbon inside the earth.

During the course of the study, scientists drilled more than 1.5 miles into the sea floor and captured samples from mines and boreholes from depths of more than 3 miles.

Data was collected from hundreds of different sites to assess what ecosystems and life forms could be present in subterranean rock within the surface of the earth. At the start of the study, it was unknown that such a rich diversity of life could exist so deep within the earth’s surface, but the biosphere they uncovered is thought to be twice the volume of the oceans.

The record depth at which microbes were found in this study was approximately three miles below the earth’s surface (which is a deep as they tested), but the absolute limits of life underground have yet to be established.

Whilst this study possibly only scratched the surface of the spectrum of underground life, the scientists estimated up to 23 billion tonnes of micro-organisms living in this “deep biosphere” – accounting for nearly 400 times the amount of carbon found in all humans.

Remarkably, deep earth life appears to have comparable genetic diversity to all life found above the surface. The so-called microbial “dark matter” of mysterious creatures consists mainly of bacteria and other single-celled organisms but also included minuscule worms and “zombie” microbes the team described as “barely alive”.

These microbes were surviving in extreme conditions with lack of nutrients and without light. One microbe was living in temperatures of 1210C around thermal vents at the bottom of the sea – a temperature that would normally kill most life forms. The implications of these findings have fuelled speculation that similar life could exist within the surface of other planets and their moons, such as Mars.

These microorganisms have shown they can survive without light, at high pressure and temperatures – which raises many unanswered questions such as where do they get their energy from in an environment lacking in nutrients? Also, how deep do these life forms live within the earth’s surface?
The scientists presented their findings before the annual meeting of the American Geophysical Union in Washington DC.

Rachel Kayani