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Clay Major Contributor To Oxygen That Enabled Early Animal Life

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  • Pat Neuman
    Clay Major Contributor To Oxygen That Enabled Early Animal Life by Staff Writers Riverside CA (SPX) Feb 03, 2006 A UC Riverside-led study has found that clay
    Message 1 of 1 , Feb 2, 2006
      Clay Major Contributor To Oxygen That Enabled Early Animal Life

      by Staff Writers
      Riverside CA (SPX) Feb 03, 2006
      A UC Riverside-led study has found that clay made animal life
      possible on Earth. A sudden increase in oxygen in the Earth's recent
      geological history, widely considered necessary for the expansion of
      animal life, occurred just as the rate of clay formation on the
      Earth's surface also increased, the researchers report.
      "Our study shows for the first time that the initial soils covering
      the terrestrial surface of Earth increased the production of clay
      minerals and provided the critical geochemical processes necessary
      to oxygenate the atmosphere and support multicellular animal life,"
      said Martin Kennedy, an associate professor of sedimentary geology
      and geochemistry at UCR, who led the study.

      Study results appear in the Feb. 2 issue of Science Express, which
      provides electronic publication of selected Science papers in
      advance of print.

      Analyzing old sedimentary rocks, the researchers found evidence of
      an increase in clay mineral deposition in the oceans during a 200
      million year period that fell between 1.1 to 0.54 billion years ago –
      a stretch of time known as the late Precambrian when oxygen
      suddenly increased in the Earth's atmosphere. The increases in clay
      formation and oxygen shortly preceded – in geological time – the
      first animal fossils about 600 million years ago.

      "This study shows how we can use principles developed from the study
      of modern environments to understand the very complex origin of life
      on our planet – studying a time in history that has left us only a
      scanty record of its conditions," said Lawrence M. Mayer, a
      professor of oceanography at the University of Maine and a co-author
      of the Science paper.

      Clay minerals form in soils through biological interactions with
      weathering rocks and are then eroded and flushed to the sea, where
      they are deposited as mud. Because clay minerals are chemically
      reactive, they attract and absorb organic matter in ocean water, and
      physically shelter and preserve it.

      The UCR-led study emphasizes the possibility that colonization of
      the land surface by a primitive terrestrial ecosystem (possibly
      involving fungi) accelerated clay formation, as happens in modern

      Upon being washed down to the sea, the clay minerals were
      responsible for preserving more organic matter in marine sediments
      than had been the case in the absence of clays. Organic matter
      preservation results in an equal portion of oxygen released to the
      atmosphere through the chemical reaction of photosynthesis. Thus an
      increase in the burial of organic carbon made it possible for more
      oxygen to escape into the atmosphere, the researchers posit.

      "One of the things we least understand is why animals evolved so
      late in Earth history," Kennedy said. "Why did animals wait until
      the eleventh hour, whereas evidence for more primitive life dates
      back to billions of years? One of the best bets to explain the
      difference is an increase in oxygen concentration in the atmosphere,
      which is necessary for animal life and was likely too low through
      most of Earth's history."

      To establish a change in clay abundance during the late Precambrian,
      the researchers studied thick sections of ancient sedimentary rocks
      in Australia, China and Scandinavia, representing a history of
      hundreds of millions of years, to identify when clay minerals
      increased in the sediment from almost nothing to modern depositional

      "We predicted we would only find a significant percentage of clay
      minerals in sediments toward the end of the Precambrian, when
      complex life arose, while earlier sediments would have less clay
      content," Kennedy said. "This test is easier than it sounds. Because
      clay minerals make up the bulk of sediment deposited today, we are
      saying that it should be largely absent in ancient rocks. And this
      is just what one finds."

      The study attracted the attention of the National Aeronautics and
      Space Administration during the proposal stage, and the agency
      helped fund the research.

      "NASA is interested in what conditions to look for on other planets
      that might lead to the arrival of life," Kennedy said. "What are the
      processes? Using Earth as our most detailed study site, what are the
      necessary steps a planet needs to go through to enable complex
      animal life to arise? If oxygen is the metabolic pathway, then we
      need to know what conditions have to allow for that to happen. The
      geologic record provides us with a record of these steps that
      occurred on Earth."

      UCR's Mary Droser and David Mrofka; and David Pevear collaborated on
      the study, which was supported also by the National Science


      Martin Kennedy, associate professor in the Department of Earth
      Sciences at UCR, led a study that identifies clay as a major
      contributor to oxygen that enabled early animal life on Earth.

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