An Inexhaustible Source of Energy from Methane in Deep Earth

Sep 15, 2004

Untapped reserves of methane, the main component in natural gas, may be found deep in Earth’s crust, according to a recently released report in the Proceedings of the National Academy of Sciences of the United States of America (PNAS). These reserves could be a virtually inexhaustible source of energy for future generations. The team of researchers from Lawrence Livermore National Laboratory, Carnegie Institution’s Geophysical Laboratory, Harvard University, Argonne National Laboratory and Indiana University, South Bend, through a series of experiments and theoretical calculations, showed that methane forms under conditions that occur in Earth’s upper mantle.

Methane is the most plentiful hydrocarbon in Earth’s crust and is a main component of natural gas. However, oil and gas wells are typically only drilled 5 to 10 kilometers beneath the surface. These depths correspond to pressures of a few thousand atmospheres.

Using a diamond anvil cell, the scientists squeezed materials common at Earth’s surface — iron oxide (FeO), calcite (CaCO3) (the primary component of marble) and water to pressures ranging from 50,000 to 110,000 atmospheres and temperatures more than 2,500 degrees Fahrenheit — to create conditions similar to those found deep within Earth.

Methane (CH4) formed by combining the carbon in calcite with the hydrogen in water. The reaction occurred over a range of temperatures and pressures. Methane production was most favorable at 900 degrees Fahrenheit and 70,000 atmospheres of pressure.

The experiments show that a non-biological source of hydrocarbons may lie in Earth’s mantle and was created from reactions between water and rock — not just from the decomposition of living organisms.

“The results demonstrate that methane readily forms by the reaction of marble with iron-rich minerals and water under conditions typical in Earth’s upper mantle,” said Laurence Fried, of Livermore’s Chemistry and Materials Science Directorate. “This suggests that there may be untapped methane reserves well below Earth’s surface. Our calculations show that methane is thermodynamically stable under conditions typical of Earth’s mantle, indicating that such reserves could potentially exist for millions of years.”

The study is published in the Sept. 13-17 early, online edition of the PNAS.

The mantle is a dense, hot layer of semi-solid rock approximately 2,900 kilometers thick. The mantle, which contains more iron, magnesium and calcium than the crust, is hotter and denser because temperature and pressure inside Earth increase with depth. Because of the firestorm-like temperatures and crushing pressure in Earth’s mantle, molecules behave very differently than they do on the surface.

“When we looked at the samples under these pressures and temperatures, they revealed optical changes indicative of methane formation,” Fried said. “At temperatures above 2,200 degrees Fahrenheit, we found that the carbon in calcite formed carbon dioxide rather than methane. This implies that methane in the interior of Earth might exist at depths between 100 and 200 kilometers. This has broad implications for the hydrocarbon reserves of the planet and could indicate that methane is more prevalent in the mantle than previously thought. Due to the vast size of Earth’s mantle, hydrocarbon reserves in the mantle could be much larger than reserves currently found in Earth’s crust.”

Explore further: Ceres bright spots sharpen but questions remain

Related Stories

New detector sniffs out origins of methane

Mar 05, 2015

Methane is a potent greenhouse gas, second only to carbon dioxide in its capacity to trap heat in Earth's atmosphere for a long time. The gas can originate from lakes and swamps, natural-gas pipelines, deep-sea ...

Some of the best pictures of the planets in our solar system

Jan 19, 2015

Our Solar System is a pretty picturesque place. Between the Sun, the Moon, and the Inner and Outer Solar System, there is no shortage of wondrous things to behold. But arguably, it is the eight planets that make up our Solar ...

Recommended for you

Ceres bright spots sharpen but questions remain

2 minutes ago

The latest views of Ceres' enigmatic white spots are sharper and clearer, but it's obvious that Dawn will have to descend much lower before we'll see crucial details hidden in this overexposed splatter of ...

What are extrasolar planets?

12 minutes ago

For countless generations, human beings have looked out at the night sky and wondered if they were alone in the universe. With the discovery of other planets in our solar system, the true extent of the Milky ...

Rosetta's view of a comet's "great divide"

22 minutes ago

The latest image to be revealed of comet 67P/Churyumov-Gerasimenko comes from October 27, 2014, before the Philae lander even departed for its surface. Above we get a view of a dramatically-shadowed cliff ...

How long will our spacecraft survive?

32 minutes ago

There are many hazards out there, eager to disrupt and dismantle the mighty machines we send out into space. How long can they survive to perform their important missions?

Why roundworms are ideal for space studies

52 minutes ago

Humans have long been fascinated by the cosmos. Ancient cave paintings show that we've been thinking about space for much of the history of our species. The popularity of recent sci-fi movies suggest that ...

A curious family of giant exoplanets

1 hour ago

There are 565 exoplanets currently known that are as massive as Jupiter or bigger, about one third of the total known, confirmed exoplanet population. About one quarter of the massive population orbits very ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.