Reserves of oil and gas, like the puddle of Venezuelan crude seen above, are made from the remains of plants and animals buried just a few miles below Earth's surface.
By mimicking the extreme conditions found much deeper, inside Earth's mantle, scientists have created the chains of carbon and hydrogen that make up so-called fossil fuels—without the fossils.
Photograph by Rebecca Hale
The study addresses the controversial view, first proposed by Soviet geologists in the 1950s, that deep Earth holds reserves of oil made from just minerals and water.
Some scientists have even suggested that material from these deeper reservoirs occasionally migrates to the surface and may help to replenish known oil fields.
Henry Scott, of Indiana University South Bend, was part of a 2004 team that made inorganic methane from marble under simulated "deep Earth" conditions.
Production of heavier hydrocarbons from methane is a "big step forward," said Scott, who was not part of the new study.
The work makes it seem increasingly likely that some abotic hydrocarbons can form in the deep Earth.
However, he cautioned, there is little to suggest that commercially important amounts of oil, gas, and other hydrocarbons have fossil-free origins.
"There is simply an overwhelming body of evidence suggesting [commercial deposits] form from the decay of once-living things," he said.
