The process of hydrocarbon production occurs in two steps. In the first, an iron compound in rock strips water of its oxygen, liberating hydrogen gas. In the second step, hydrogen gas and carbon dioxide (from the degassing of magma) combine to produce methane and water. The Minnesota team discovered that rocks rich in chromium minerals accelerate the second step, while also producing more complex hydrocarbons–ethane and propane. Both likely serve as food for some bacteria.
“The second step is a reaction well known to chemists,” said Seyfried, a professor of geology and geophysics. “But in several papers published in the last few years, researchers have noted great difficulty in forming hydrocarbons more complex than methane. Dionysios [Foustoukas] showed that in the presence of chromium-bearing minerals, it could happen.
“Chemists might want to tweak this process and see if they can produce hydrocarbons more efficienty. But we want to get clues about what goes on in hydrothermal vents and to understand how hydrocarbon gases are generated in the continental and oceanic crust.”
In related work, Seyfried and and his colleague Kang Ding have built chemical sensors that can be placed in hydrothermal vents to measure such items as acidity and the amounts of gases like hydrogen and hydrogen sulfide, which also serve as energy sources for microbial communities. Acidity also seems to play a role in hydrocarbon synthesis in submarine hydrothermal systems. To access the vents as deep as two miles beneath the sea surface, the researchers use the submersible ALVIN; they have now dived to a number of vent sites.
Text for this article comes from a University of Minnesota press release.