New findings about carbon deep beneath the Earth's surface suggest it might have influenced the history of life on the planet - and diamonds.

There is little understanding of how carbon behaved deep below the Earth's surface so researchers have created a model to try and calculate how much carbon and what types exist in fluids at 100 miles below the Earth's surface at temperatures up to 2,100 degrees F. 

They believe that in addition to the carbon dioxide and methane already documented deep in subduction zones, there exists a rich variety of organic carbon species that could spark the formation of diamonds and perhaps even become food for microbial life. This hypothetical model, called the Deep Earth Water model, calculated the chemical makeup of fluids in the Earth's mantle, expelled from descending tectonic plates. Some of the fluids, those in equilibrium with mantle peridotite minerals, contained the expected carbon dioxide and methane. But others, those in equilibrium with diamonds and eclogitic minerals, contained dissolved organic carbon species including a vinegar-like acetic acid.  

These high concentrations of dissolved carbon species, previously unknown at great depth in the Earth, suggest they are helping to ferry large amounts of carbon from the subduction zone into the overlying mantle wedge where they are likely to alter the mantle and affect the cycling of elements back into the Earth's atmosphere.

The team also suggested that these mantle fluids with dissolved organic carbon species could be creating diamonds in a previously unknown way. Scientists have long believed diamond formation resulted through chemical reactions starting with either carbon dioxide or methane. The organic species offer a range of different starting materials, and an entirely new take on the creation of the gemstones.