Global methane release about 600 million years ago
- Study finds evidence for global methane release about 600 million years
December 18, 2003
New findings may have implications for the stability of today's climate
Scientists at the University of California, Riverside and Columbia
University have found evidence of the release of an enormous quantity of
methane gas as ice sheets melted at the end of a global ice age about 600
million years ago, possibly altering the ocean's chemistry, influencing
oxygen levels in the ocean and atmosphere, and enhancing climate warming
because methane is a powerful greenhouse gas. The study was published in
today's issue of the journal Nature.
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
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 associated with significant climate change in the Earth's
history, and they are a large and exceedingly unstable source of
greenhouse gas, greater than the equivalent of instantaneously burning
all the oil reserves on Earth.
"Linking these dramatic climate events to changes in the methane
clathrate pool has important implications for the stability of our
current climate," said Martin Kennedy, an associate professor of geology
at UC Riverside. "The Earth has a large unstable pool of these clathrates
in ocean sediments today, and it is thought that a few degrees of ocean
warming could trigger large-scale release into the atmosphere. We now
have strong evidence of this doomsday scenario in one of the most
important intervals of Earth's biologic history".
The recognition of extreme isotope variability in the rocks examined in
south China is expected to stimulate new research.
"This is a very exciting result because the existence of methane seeps
and their possible significance in explaining the unusual carbon isotopic
signature of the carbonate deposits had been discounted by many on the
basis of the lack of expected isotopic heterogeneity," said Nicholas
Christie-Blick, a professor of earth and environmental sciences at the
Lamont-Doherty Earth Observatory of Columbia University. "If the methane
hydrate hypothesis is borne out by new studies that are sure to be
stimulated by this research, it represents one more reason for
questioning why the snowball Earth edifice is needed."
The National Science Foundation's (NSF) division of earth sciences funded
the research. NSF is the federal agency responsible for supporting basic
science, engineering and education research. NSF is an independent
federal agency that supports fundamental research and education across
all fields of science and engineering, with an annual budget of nearly
University of California - Riverside
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