Methane Warmed Ancient 'Snowball Earth'

May 28, 2008 -- The melting of methane ice unleashed runaway global warming some 635 million years ago, according to a study released Wednesday that has implications for today's climate-change crisis.

Release of the potent greenhouse gas, at first in small amounts and then in massive volumes, brought a sudden end to the planet's longest Ice Age, the study's authors believe.

During the so-called "Snowball Earth" era, Earth froze over completely, with glaciers that crept down into the tropics and possibly even reached the equator.

The chill was self-sustaining, because the ice formed a brilliant white shell that reflected the sun's rays, preventing the surface from warming.

After a frozen slumber lasting 155 million years, Earth warmed dramatically.

How this happened has been fiercely disputed, although all agree that the event changed the planet's climate system and ocean chemistry forever.

Publishing in the weekly British journal Nature, scientists in the United States and Australia point the finger at methane clathrates -- methane-rich ice that forms under ice sheets at specific temperatures and pressures.

The researchers believe that the ice sheets on Snowball Earth became unstable, which released pressure on the clathrates.