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Global methane release about 600 million years ago

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  • npat1@juno.com
    Study finds evidence for global methane release about 600 million years ago December 18, 2003 New findings may have implications for the stability of today s
    Message 1 of 1 , Feb 6, 2004
      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
      $5.3 billion.
      University of California - Riverside

      Century may bring unprecedented climate change to southern hemisphere
      February 6, 2004

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