Mantle mockup. Methane bubbles (at the bottom, left and slightly right of center) in a lab simulation of Earth's interior suggest that the gas may form in the mantle.

Methane in the Mantle?

Earth's supply of fossil fuels may not depend entirely on fossils after all. For the first time scientists have created methane gas in the lab using only inorganic materials, leading to speculation that vast reserves of the gas may be present deep underground.

The conventional wisdom is that fossil fuels typically derive from ancient plants or organisms. A few scientists have long speculated, however, that oil and gas could arise in the absence of organic matter. The late astrophysicist Thomas Gold of Cornell University was one of the strongest proponents of the idea. He suggested that the biological molecules found in oil and gas are not proof of a biological origin but instead are traces of microscopic organisms that thrive deep in the crust. In recent years, Gold's theory that organisms live beneath the surface has proved correct. But until now, nobody has been able to demonstrate that hydrocarbons could be produced without the byproducts of life.

The breakthrough came when a team led by geophysicist Henry Scott of Indiana University in South Bend used an apparatus called a diamond anvil cell to heat and squeeze iron oxide, calcite, and water. The experiment was intended to mimic conditions 100 km to 200 km deep, in the partially molten layer known as the mantle. At temperatures between 500° and 1500°C and pressures between 50,000 and 110,000 atmospheres, methane bubbles formed, the team discovered by sending x-rays through the sample. The results, published online this week in the Proceedings of the National Academy of Sciences, point to the possibility of a huge reservoir of methane in the mantle. But even if such a reservoir exists, it's out of reach with today's technology; the typical oil or gas well is rarely deeper than 10 km.

The findings have implications for the possibility of life on other planets as well, says geologist Barbara Sherwood Lollar of the University of Toronto. The methane recently detected on Mars (ScienceNOW, 24 Mars) may not indicate life, because it could have been produced from simple elements. On the other hand, a deep hydrocarbon reservoir could be a source of energy for subsurface microbes. "It would provide them with the energy they need to subsist in the absence of photosynthesis," Lollar says.

Related sites
Henry Scott's research
Thomas Gold's obituary

Posted in Earth