Eric I don't know about that theory, but considering the number of mass extinction events that occurred, it certainly is possible. A major volcanic eruption could spew enough ash into the atmosphere to cut down the sun enough to cause global cooling and depending on the length and extent could cause some species extinction.
Peter
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Peter Kaufman NRA Life GOA SAF RKCC CM-023 RKS #5642 SHAG # 005 Ironwood Nut Life is too short to have ugly knives