CLIMATOLOGY

A Hot Record of a Cooling Climate

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Science  19 Oct 2001:
Vol. 294, Issue 5542, pp. 479-481
DOI: 10.1126/science.294.5542.479e

Earth's climate has generally cooled during the past 50 million years or so. Large ice sheets first formed in Antarctica, though the exact timing of their growth has been debated. Their development is important because the presence of large ice sheets affects Earth's climate and oceans greatly.

When magma intrudes into the upper crust, its heat drives vigorous hydrothermal systems, as is currently happening, for example, in Yellowstone Park and in New Zealand. The heated ground water alters the rocks of the shallow crust. The hydrogen isotope composition of the altered rocks can then provide information about the air temperatures when the water evaporated and formed as rain or snow. By analyzing fossil hydrothermal systems of different ages, Dallai et al. show that the temperatures over Antarctica cooled dramatically about 40 million years ago, consistent with an onset of glaciation shortly thereafter.—BH

Geology29, 931 (2001).

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