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Ancient Pebbles Contain Evidence Of A Hotter World
Stanford CA (SPX) May 26, 2004 Analysis of 3.2-billion-year-old pebbles has yielded perhaps the oldest geological evidence of Earth's ancient atmosphere and climate. The findings, published in the April 15 issue of the journal Nature, indicate that carbon dioxide levels in the early atmosphere were substantially above those that exist today and above those predicted by other models of the early Earth. The research implies that carbon dioxide, perhaps aided by another greenhouse gas such as methane, helped to keep the planet warm enough for life to form and evolve. "The early mix of greenhouse gases is relevant to the evolution of atmospheric oxygen and the conditions in which life arose," said Angela Hessler, a geology professor at Grand Valley State University, who completed the research as a doctoral student at Stanford University. "A more detailed picture of early Earth might serve as a proxy for exploring the history of nearby planets in the solar system." Stanford geologists Donald R. Lowe and Dennis K. Bird, and senior Stanford researcher Robert E. Jones, also contributed to the research.
Early to rise? The exact mix of these ancient greenhouse gases is poorly understood, in large part because of the paucity of data. Weathering rinds -- discolorations near the surface of pebbles that give evidence of reactions that occurred billions of years ago with the primeval atmosphere -- offer useful evidence. But the steady churning of the Earth's crust through plate tectonics ensured that most of these pebbles, and all their accompanying information, have long since been recycled. The researchers say the pebbles they analyzed, found in drill cores taken at the Royal Sheba gold mine in South Africa, were rolled into smooth, round shapes in a 3.2 billion-year-old river or stream system. "This outcrop [in South Africa] is unique in its preservation," Bird said. "Few remain that haven't been modified in some way by tectonic and metamorphic processes."
Rising atmosphere This amount is several times higher than the amount of carbon dioxide in the atmosphere today, consistent with the current understanding that life evolved in a dramatically different environment than exists today. Other research by the Stanford group suggests that carbon dioxide levels gradually declined during the 500 million years after the formation of the pebbles. As the continents became stable, and surface weathering and photosynthesis evolved, it is likely that carbon dioxide was more readily removed from the atmosphere. Methane, another greenhouse gas produced by decaying biomass, may have combined with carbon dioxide to maintain warm or even hot surface temperatures. Earlier work by the study's authors suggests that surface temperatures on the 3.2-billion-year-old Earth may have topped 60 degrees Celsius (140 degrees Fahrenheit). Geologic samples with evidence of atmospheric chemistry in the Archaean Eon, the first two billion years of Earth's history, are separated by 500 million years. So despite the new information in the Nature study, attempts to understand Earth's ancient history still involve lots of inferences and educated guesses. The authors, whose research was funded by the NASA Exobiology Program and the National Science Foundation, agree on the need for more hard evidence. "There can be little doubt about the importance of empirical geologic observations for constraining future climate models of Earth's early atmosphere," they wrote. Community Email This Article Comment On This Article Related Links Stanford SpaceDaily Search SpaceDaily Subscribe To SpaceDaily Express Dirt, rocks and all the stuff we stand on firmly
Magnetic Reconnection Region Larger Than 2.5 Million Km Found In The Solar Wind
Paris (ESA) Jan 12, 2006Using the ESA Cluster spacecraft and the NASA Wind and ACE satellites, a team of American and European scientists have discovered the largest jets of particles created between the Earth and the Sun by magnetic reconnection. This result makes the cover of this week's issue of Nature. |
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