GEOLOGY: When Mountains Rose Up

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Science  18 Feb 2000:
Vol. 287, Issue 5456, pp. 1169d
DOI: 10.1126/science.287.5456.1169d

Formation of mountains affects Earth's climate, ecosystems, and evolution. In many areas, the uncertainty in the age of formation of Earth's high topography is tens of millions of years. Because of this uncertainty, the relation between formation of topography and tectonic processes also is unclear, as is the role of weathering and denudation in limiting high topography.

One way to measure relief is to use the known effect that the oxygen and hydrogen isotope ratios of precipitation decreases with elevation. Chamberlain and Poage thus looked at minerals formed from rain water worldwide to develop a relation between isotopic composition and relief. They then applied this approach to show that the topography of the Southern Alps in New Zealand formed about 5 million years ago whereas that of the Sierra Nevada in California formed about 16 million years ago. The age for the Southern Alps is consistent with another study by Batt et al., who examined the cooling rates of rocks close to the Alpine Fault, the major fault through the Alps, thus connecting tectonic and topographic processes.—BH

Geology 28, 115 (2000); Geol. Soc. Am. Bull.112, 250 (2000).

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