The global ice age is of particular interest to paleobiologists because it took place shortly before the first appearance of animals in the fossil record, and may have supplied an environmental drive to evolution. The Earth's most severe climate is thought to have occurred about 600 million years ago with ice sheets stretching to the tropics. Some scientists have referred to times of such extreme cold as a "snowball Earth" condition, assuming that the ocean would have been totally ice covered.
The new evidence is based on a chemical fingerprint of the methane gas from rocks in south China, which is strongly enriched in lighter carbon isotope, carbon-12, and which the researchers measured in ancient ocean carbonate sediments that were deposited as the temperature rose. The methane gas was apparently derived from the melting of frozen methane clathrate crystals that had accumulated beneath the seafloor.
"The extremely negative isotopic values from these sediments provide unambiguous evidence for methane-derived carbon," said Ganqing Jiang, a researcher at the University of California, Riverside, and the article's lead author. "The identification of a methane-derived isotope signal and widespread seep-like deposits indicate the massive passage of methane through the sediments," he added. "We now have an important record of the role methane plays in climate change and the global carbon cycle."
Methane clathrates are increasingly thought to play a role in mass extinctions associa
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Contact: Ricardo Duran
ricardo.duran@ucr.edu
909-787-5893
University of California - Riverside
17-Dec-2003