Cold and ice, not heat, episodically gripped tropical regions 300 million years ago

July 31, 2008
Cold and ice, not heat, episodically gripped tropical regions 300 million years ago

Unaweep Canyon in the Rocky Mountains is the site of a deep gorge that reveals ancient landscapes and sediments. The inset image is of a "dropstone" from an eons-old glacier. Credit: Gerilyn Soreghan

Geoscientists have long presumed that, like today, the tropics remained warm throughout Earth's last major glaciation 300 million years ago.

New evidence, however, indicates that cold temperatures in fact episodically gripped these equatorial latitudes at that time.

Geologist Gerilyn Soreghan of Oklahoma University found evidence for this conclusion in the preservation of an ancient glacial landscape in the Rocky Mountains of western Colorado. Three hundred million years ago, the region was part of the tropics. The continents then were assembled into the supercontinent Pangaea.

Soreghan and colleagues published their results in the August 2008, issue of the journal Geology.

Climate model simulations are unable to replicate such cold tropical conditions for this time period, said Soreghan. "We are left with the prospect that what has been termed our 'best-known' analogue to Earth's modern glaciation is in fact poorly known."

"This study is an example of the wealth of untapped climate information stored in Earth's 'deep time' geologic record millions of years ago," said H. Richard Lane, program director in NSF's Division of Earth Sciences, which funded the research. "These kinds of discoveries may greatly improve our understanding and prediction of modern climate change."

As a result of the close proximity of the ancient tropical glaciers to the sea, the toes of the glaciers were likely less than 500 meters above sea level--much lower than the tropical glaciers of Earth's recent glacial times.

"The Late Paleozoic tropical climate was not buffered against cold from the high latitudes, as everyone had thought," said Soreghan. "The evidence we found indicates that glaciers were common at this time, even in tropical latitudes. This calls into question traditional assumptions of long-lasting equatorial warmth in the Late Paleozoic, and raises the possibility of large-scale and unexpected climate change in the tropics during that time."

Source: National Science Foundation

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out7x
Aug 01, 2008

Rank: 3.3 / 5 (3)
Paleo-Climates are not understood well, due to different continent positions, ocean currents,and atmosphere composition. The antarctic was tropical, eventhough it was high latitude, 40-100Myr ago(cretaceous thru eocene).
D666
Aug 01, 2008

Rank: 4.5 / 5 (2)
I think the title should more accurately read "Cold and ice, AS WELL AS heat, episodically gripped ... etc". By definition, they're hot right now, and this is an episode.
jeffsaunders
Aug 04, 2008

Rank: 5 / 5 (1)
I agree with D666 lets get the basics right and go from there.

Plus. we might want to double check that that location really was in the tropics at that time as geology of drift is not that accurate.

Plus. There have been times when the planet was complete frozen from pole to pole so it not surprising that at some time there were glaciers in the tropics.

What we need is a time line image showing average temperatures by location which includes positions of land masses locations.

Perhaps we should get Google to put one together for us. Probably only take them a few months and Ohhh what a research tool that would be.
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