When Methane Made Climate; July 2004; Scientific American Magazine; by James F. Kasting; 8 Page(s)

About 2.3 billion years ago unusual microbes breathed new life into young Planet Earth by filling its skies with oxygen. Without those prolific organisms, called cyanobacteria, most of the life that we see around us would never have evolved. Now many scientists think another group of single-celled microbes were making the planet habitable long before that time. In this view, oxygen-detesting methanogens reigned supreme during the first two billion years of Earth's history, and the greenhouse effect of the methane they produced had profound consequences for climate.

Scientists first began to suspect methane's dramatic role more than 20 years ago, but only during the past four years have the various pieces of the ancient methane story come together. Computer simulations now reveal that the gas - which survives about 10 years in today's atmosphere - could have endured for as long as 10,000 years in an oxygen-free world. No fossil remains exist from that time, but many microbiologists believe that methanogens were some of the first life-forms to evolve. In their prime, these microbes could have generated methane in quantities large enough to stave off a global deep freeze. The sun was considerably dimmer then, so the added greenhouse influence of methane could have been exactly what the planet needed to keep warm. But the methanogens did not dominate forever. The plummeting temperatures associated with their fading glory could explain Earth's first global ice age and perhaps others as well.