Monday, November 29, 1999

Fossil evidence challenges Younger Dryas Impact theory

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Washington, June 17 (ANI): A new study has found evidence against a theory, which claimed that a meteor explosion or impact thousands of years ago caused catastrophic fires over much of North America and Europe and triggered an abrupt global cooling period, called the Younger Dryas.In fact, proponents of the theory, suggested that the impact resulted in "carbonaceous spherules" and nanodiamonds-both of which they claimed were formed by intense heat.However, a new study has challenged the theory by claiming that those supposed clues are nothing more than fossilized balls of fungus, charcoal, and fecal pellets.Moreover, these naturally occurring organic materials, some of which had likely been subjected to normal cycles of wildfires, date from a period of thousands of years both before and after the time that the Younger Dryas period began -- further suggesting that there was no sudden impact event."People get very excited about the idea of a major impact causing a catastrophic fire and the abrupt climate change in that period, but there just isn't the evidence to support it," said Andrew C. Scott of the Department of Earth Sciences at Royal Holloway, University of London, who led the research.The Younger Dryas impact event theory holds that a very large meteor struck Earth or exploded in the atmosphere about 12,900 years ago, causing a vast fire over most of North America, which contributed to extinctions of most of large animals on the continent and triggered a thousand-year-long cold period.While there is much previous evidence for the abrupt onset of a cooling period at that time, other researchers have theorized that the climatic change resulted from increased freshwater in the ocean, changes in ocean and atmospheric circulation patterns, or other causes unrelated to impacts.The impact-theory proponents point to a charred layer of sediment filled with organic material that they say is unique to that period as evidence of such an event.These researchers described carbon spheres, carbon cylinders, and charcoal pieces that they conclude are melted and charred organic matter created in the intense heat of a widespread fire.Scott and his fellow researchers analyzed sediment samples to determine the origins of the carbonaceous particles.After comparing the fossil particles with modern fungal ones exposed to low to moderate heat (less than 500 degrees Celsius, or 932 degrees Fahrenheit), Scott's group concludes that the particles are actually balls of fungal material and other ordinary organic particles, such as fecal pellets from insects, plant or fungal galls, and wood, some of which may have been exposed to regularly-occurring low-intensity wildfires."There is a long history of fire in the fossil record, and these fungal samples are common everywhere, from ancient times to the present. These data support our conclusion that there wasn't one single intense fire that triggered the onset of the cold period," said Scott.The findings will be published in Geophysical Research Letters, a journal of the American Geophysical Union (AGU). (ANI)

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