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Vulcanism and Impacts
Emp is correct that flood basalts are an important factor in explaining past extinction events. One notable absence from the list of such deposits is that of the Columbia Plateau in the northwest US. During late Miocene and early Pliocene times (between 17 and 6 million years ago), one of the largest basaltic lava floods ever to appear on the earth's surface engulfed about 63,000 square miles of the Pacific Northwest. Over a period of perhaps 10 to 15 million years lava flow after lava flow poured out, eventually accumulating to a thickness of more than 6,000 feet. However, most of the lava flowed during the first 1.5 million years. Being that the molten flooding occured on the cusp of recent geologic epochs, the eruptions are linked to the extinctions of many large mammals.
http://vulcan.wr.usgs.gov/Volcanoes/ColumbiaPlateau/framework.html
Recent detractors from the impact theory for the vast K-T extinction event provide solid evidence that the an impact(s) was not the ONLY factor in the mass extinction. According to Gerta Keller, a paleontologist of Princeton University, the impact of a meteor or comet in the Late Cretaceous was "the straw that broke the camel's back" and not the sole cause of extinctions. Furthermore, it has long been known that dinosaurs were in decline when a geologically sudden event authored their demise. Of course, many other species went with them, though in separate ecosystems. While the sequence of events may be argued, it does seem clear that more than one factor triggered the K-T carnage.
http://www.sciencedaily.com/releases/2003/09/030926065930.htm
Emp is correct that flood basalts are an important factor in explaining past extinction events. One notable absence from the list of such deposits is that of the Columbia Plateau in the northwest US. During late Miocene and early Pliocene times (between 17 and 6 million years ago), one of the largest basaltic lava floods ever to appear on the earth's surface engulfed about 63,000 square miles of the Pacific Northwest. Over a period of perhaps 10 to 15 million years lava flow after lava flow poured out, eventually accumulating to a thickness of more than 6,000 feet. However, most of the lava flowed during the first 1.5 million years. Being that the molten flooding occured on the cusp of recent geologic epochs, the eruptions are linked to the extinctions of many large mammals.
http://vulcan.wr.usgs.gov/Volcanoes/ColumbiaPlateau/framework.html
Recent detractors from the impact theory for the vast K-T extinction event provide solid evidence that the an impact(s) was not the ONLY factor in the mass extinction. According to Gerta Keller, a paleontologist of Princeton University, the impact of a meteor or comet in the Late Cretaceous was "the straw that broke the camel's back" and not the sole cause of extinctions. Furthermore, it has long been known that dinosaurs were in decline when a geologically sudden event authored their demise. Of course, many other species went with them, though in separate ecosystems. While the sequence of events may be argued, it does seem clear that more than one factor triggered the K-T carnage.
http://www.sciencedaily.com/releases/2003/09/030926065930.htm