Post by Chicago Astronomer - Astro Joe on Oct 11, 2006 21:43:59 GMT -6
Adler Astronomer chimes in on Species Extinction
A wobble in Earth's orbit that causes climate change may explain why some species disappear and others emerge at seemingly regular intervals, according to a study in the journal Nature.
Utrecht University researchers in the Netherlands, studying rodent fossils from Spain spanning 22 million years, found that the rate of emergence and decline of the mammals followed cycles of about 1.2 million and 2.4 million years.
The 2.4 million-year cycles correspond with periods when the Earth's elliptical orbit becomes nearly circular, and the 1.2 million-year cycles conform to ages when the planet's tilt, which varies over the centuries, holds steady for about 200,000 years, the researchers said. Both cycles would cool the Earth and allow ice sheets to expand, forcing species to adapt or die out.
Volcanic activity, movements in Earth's tectonic plates and the amount of carbon dioxide in the atmosphere contribute to species turnover as well, said Larry Ciupik, an astronomer at the Adler Planetarium in Chicago.
Source: www.startribune.com/722/story/736693.html
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Good to be referenced...
