Geology

When It's Cold Down South

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Science  13 May 2011:
Vol. 332, Issue 6031, pp. 769
DOI: 10.1126/science.332.6031.769-c

Earth's climate cooled markedly over the past 65 million years, changing from a world with forests and dinosaurs near the poles to one with huge ice sheets in Antarctica and much lower sea levels. A marked decrease in atmospheric CO2 levels probably drove this cooling; a further important change was that plate motions isolated Antarctica from the other continents. Temperature records have been available from the oceans and other continents, where a variety of biological records can be tapped, but not from Antarctica for comparison. Dallai and Burgess have now constructed an initial temperature record using hydrogen isotopes in minerals in Antarctic igneous rocks altered by hydrothermal fluids at specific dated times in the past. These fluids tap surface waters where the isotopic ratio in part reflects temperature, and hydrogen is regularly exchanged between fluids and OH-bearing minerals. The record, although rough and in some cases supported with limited data, shows cooling after about 40 to 45 million years ago by more than 10°C and a suggestion of some significant oscillations.

Geology 39, 423 (2011).

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