Origin of the massive methane reservoir identified

A new study by the Woods Hole Oceanographic Institution (WHOI) published on 19 August 2019 in the Proceedings of the National Academy of Sciences provides evidence of the formation and abundance of abiotic methane – methane formed by chemical reactions involving no organic matter – on Earth and shows how the gases could have a similar origin on d. other planets and moons, even those containing no more liquid water. Researchers have long noted the methane released by deep-sea mouths. But while gas is abundant in the atmosphere where it is produced by living beings, the source of methane at the bottom of the sea was a mystery.

"The identification of an abiotic source of high-seas methane is a problem we have been struggling with for many years," says Jeffrey Seewald, senior scientist at WHOI, who studies geochemistry in hydrothermal systems.

Of the 160 rock samples analyzed from the world's oceans, almost all contained pockets of methane. These oceanic deposits constitute a reservoir exceeding the amount of methane in the Earth's atmosphere prior to industrialization, says Frieder Klein, marine geologist at WHOI and lead author of the study.

"We were totally surprised to find this huge reservoir of abiotic methane in the oceanic crust and mantle," Klein said.

Scientists analyzed the rocks using Raman spectroscopy, a laser microscope allowing them to identify the fluids and minerals contained in a thin slice of rock. Almost every sample contained an assemblage of minerals and gases that form when seawater, passing through the deep oceanic crust, is trapped in olivine with magma. When the mineral cools, the water trapped inside undergoes a chemical reaction, a process called serpentinization, which forms hydrogen and methane. The authors demonstrate that in otherwise inhospitable environments, only two ingredients, water and olivine, can form methane.

"Here is a source of chemical energy created by geology," said Seewald.

On Earth, deep-sea methane could have played a crucial role in the evolution of primitive organisms living in hydrothermal vents at the bottom of the sea, says Seewald. And elsewhere in the solar system, in places like Europa, the moon of Jupiter, and Saturn's Enceladus, methane produced by the same process could be a source of energy for basic life forms.