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Rodents tell a geologic tale

From Ottawa, at a meeting of the Society of Vertebrate Paleontology

The discovery of previously unknown rodent species that lived in Chile millions of years ago suggests that mountains in the southern Andes first rose to significant heights at least 18 million years ago.

By measuring the proportions of radioactive isotopes in ash deposits, scientists can estimate the date but not the height of a particular volcanic eruption. Therefore, geologists haven't been able to determine when the southernmost portions of South America's Andes, as a whole, rose to their current heights, says Jill Wertheim, a paleontologist at the University of California, Santa Barbara. Fossils could provide the answer.

Wertheim and her colleagues studied fossils of small animals from a part of that area that's now hundreds of meters high. More than 20 million years ago, however, the region would have sat close to sea level along the Pacific coast, she notes.

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