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BOB HIRSHON (host):
Cycles of exinction. I’m Bob Hirshon and this is Science Update.
Not all extinctions are due to comet strikes or overhunting. In fact, new research shows that long-term cycles in the Earth’s orbit and the tilt of its axis may be responsible for a regular rhythm of species extinction and creation. Paleontologist Jan van Dam of Utrect University in the Netherlands found the connection by charting turnover in the fossil record of rodent species.
JAN VAN DAM (Utrect University):We found periods of two and a half million years, and another period of about one million years, and these are exactly the same frequencies which are known from astronomical calculations. So that made us think that there could be a connection.
HIRSHON:
Van Dam says these cycles in Earth’s orbit and tilt may have caused periods of global cooling, which in turn could have caused some mammals to perish while others flourished. I’m Bob Hirshon, for AAAS, the science society.