Magazine article Oceanus

Shifting Continents and Climates

Magazine article Oceanus

Shifting Continents and Climates

Article excerpt

Sixty-five millions years ago, dinosaurs had just become extinct, and mammals were starting to dominate the planet. Tropical conditions extended to Northern Spain and the heartland of North America. Large trees grew in Greenland and Antarctica, and alligators and primates could be found on Ellesmere Island in Arctic Canada. Global temperatures were 6[degrees] to 10[degrees]G (11[degrees] to 18[degrees]F) warmer than today, and the polar regions were free of ice.

Since then, Earth's history has been marked by a sustained and nearly continuous cooling trend, punctuated by abrupt shifts and transitions. Today, Homo sapiens dominate the landscape, the poles are blanketed in ice, and over the past 3 million years, massive continental glaciers have waxed and waned in an ongoing era of ice ages. Our modern climate is a brief, temperate respite from an otherwise cold cycle in Earth's geologic life.

So how did our hothouse planet turn into an icehouse planet?

Tectonic causes, climatic effects

One explanation for the change is the steadily and substantially decreasing levels of carbon dioxide and other greenhouse gases in the atmosphere (at least until the anomalous and very recent post-Industrial Revolution era). Less greenhouse gas means that less heat is trapped in Earth's atmosphere.

But changes in Earth's atmosphere cannot explain the full extent of global cooling or periods of acute change. Nor can scientists fully explain the causes of the atmospheric changes themselves. …

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