The research papers, appearing in the January 26 issue of Science and a forthcoming issue of Earth and Planetary Science Letters, mean scientists will have to re-evaluate tectonic processes that build high elevation plateaus, such as those in Tibet and the central Andes.
"These results really change the paradigm of understanding of how mountain belts grow," says Garzione, coauthor of both papers. "We've always assumed that the folding and faulting in the upper crust produced high elevation mountains. Now we have data on ancient mountain elevation that shows something else is responsible for the mountains' uplift."
Garzione took a new approach to paleoaltimetry, the tricky science of measuring mountain height from the distant past. As mountains lift, weather erodes them, complicating the estimation of how high they might be at any given time. Until Garzione's research, geologists estimated surface uplift by examining leaf fossils to determine at what elevation the plants lived, or by dating when certain minerals began moving rapidly to the surface. Unfortunately, plant characteristics can change radically over millions of years, and changes in climate can also cause erosion, throwing a significant question mark into the equation.
Garzione instead focused on the products of that erosion. As mountains are eroded, their sediment is carried down the slope in streams and collected at the base of the forming mountain range. As a mountain range rises, it experiences different atmospheric conditions simply due to its change in height. Those atmospheric changes, such as temperature and the amount and composition of rainfall are recorded in minerals that grow near the surface at different altitudes on the mountainside. Garzione wrote her doctoral dissertation on the possibility of retrieving that atmospheric information from the ancient sediment, dating it, and forming a record of a mountain belt's uplift history.
Garzione's recent work concentrated on the Bolivian Altiplano, which is a large, high elevation basin in the Andes Mountains in South America. There she took samples of sedimentary rock that had accumulated between 12 and 5 million years ago from erosion of the surrounding ranges. Garzione analyzed the samples using two methods, and both studies yielded the same results: Between 10 and 7 million years ago, the Andes shot up.
"When I first showed this data to others, they had a hard time believing that mountains could pop up so quickly," says Garzione. "With supporting data from the new paleotemperature technique, we have more confidence in the uplift history and can determine processes that caused the mountains to rise.
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Data shows mountains rise faster than expected
Garzione
wo new studies by Carmala Garzione, assistant professor of earth and environmental sciences, show that mountain ranges rise to their height in as little as two million years--several times faster than geologists have always thought. Each of the findings came from two pioneering methods of measuring ancient mountain elevations, and the results are in tight agreement.
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