Wobbly planet Earth: Photo courtesy NASA.
The extinction of rodents and other mammals have been linked to variations in the Earth’s tilt and orbit, according to new research published in the journal Nature.
Dutch scientists studying 22 million year old rodent fossils in central Spain found that the rise and fall of the mammal species correlated with cooling periods due to changes in the Earth’s behavior. Rodents offer one of the best fossil mammal records and are excellent indicators of seasonal changes because of their short life spans.
"Extinctions in rodent species occur in pulses which are spaced by intervals controlled by astronomical variations and their effects on climate change," Dr Jan van Dam, of the Utrecht University in the Netherlands, said.
The researchers discovered two cycles associated with changes in climate, habitat and food availability are linked to the disappearance of rodent species. One cycle, which lasts 2.4 million years, is linked to variations in the Earth’s orbit. The other 1.2 million year cycle is related to changes in the tilt of the Earth’s axis. Both cycles would cool the Earth, allowing the expansion of ice sheets and causing species to adapt or die out.
Right now Earth is in a relatively circular orbit and about 700,000 years away from the next period of axis stability.
"The environment is responsible to what happens to species," said Van Dam. "Biological factors are secondary, according to our results."
However, Larry Ciupik, an astronomer at Chicago’s Adler Planetarium says volcanic activities, plate tectonics and the amount of carbon dioxide in the atmosphere also contribute to species turnover.
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