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Deeper earth conditions create ethane abiogenically by Adam Duckett |
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Researchers mimicked the conditions of the upper mantle using a laser heat source | |
HEAVY hydrocarbons can be created in the upper mantle without the need for organic matter, researchers say.
Conventional thinking is that the oil and gas we use in everyday life is formed from dead microorganisms that were compressed beneath layers of sediment subducted deep into the Earth’s crust. This crust ranges from between 5 and 70 km in depth with the layer below, called the upper mantle, extending a further 340 km beneath. Though it is hard to imagine life evolving to survive the excessive pressures and temperatures found at this depth, it has been theorised that these extreme conditions could produce methane from the iron oxide, calcium carbonate, and water believed to be present in the upper mantle and immediately overlying subducted crust.
Now, new research from the US’ Carnegie Institution’s Geophysical Laboratory says its lab tests show that this methane could be converted into a variety of heavier hydrocarbons and that they could then seep up through the crust and contribute to the biogenic reserves that we tap to power our cars and cook our food. Proponents of the theory, who stand on the fringes of petroleum engineering thinking say that if the process is occurring it could negate concerns surrounding peak oil.
Researchers mimicked the conditions of the upper mantle using a laser heat source and a bench-top diamond anvil cell to subject methane to pressures 20,000 times that at sea level and temperatures ranging from 1300oF to over 2240oF. The methane reacted to produce ethane, propane, butane, molecular hydrogen and graphite. Taking the ethane produced and subjecting it to the same conditions the researchers found they could convert it back to ethane. This reversibility, they say, suggests that the synthesis of saturated hydrocarbons is thermodynamically controlled and does not require organic matter.
Study collaborator Vladimir Kutcherov from Russia’s Lomonosov Moscow State Academy of Fine Chemical Technology says: “The notion that hydrocarbons generated in the mantle migrate into the Earth's crust and contribute to oil-and-gas reservoirs was promoted in Russia and Ukraine many years ago. The synthesis and stability of the compounds studied here as well as heavier hydrocarbons...now needs to be explored. In addition, the extent to which this 'reduced' carbon survives migration into the crust needs to be established. These and related questions demonstrate the need for a new experimental and theoretical programme to study the fate of carbon in the deep Earth."
The research is published in Nature Geoscience (doi:10.1038/ngeo591
