Mountain Building and Global Cooling
Thursday, October 26, 2006 2:58:50 PM
What's unusual about the Ordovician period is that island arcs were being uplifted onto a continent. The ones in the Pacific Ocean now are mostly underwater. The crustal plate underneath what is now the Atlantic Ocean pushed against the eastern side of North America, lifting ancient volcanic rock up from the seafloor and onto the continent. Volcanic rock weathers quickly. It reacts with CO2 and water, and the rock disintegrates. Carbon from the CO2 is trapped in the resulting sediment.
The chemical reaction that weathered away part of the Appalachians would have consumed large amounts of CO2 from the atmosphere - right around the time that the Ordovician ice age began.
The Ordovician period started out warm, with high sea levels worldwide. It ended cold, with low sea levels as glaciers covered the poles and portions of the continents. According to the study, most of the Appalachian weathering took place over 7 or 8 million years -- a very short time, by geological standards -- as the climate moved from one extreme to the next (a.o. culminating in mass extinctions of ocean life).
The rise and subsequent weathering of the Himalayas may have caused our current ice age, the one that began 40 million years ago. In the Himalayas, the process would have been the same as in the Appalachian - volcanic rocks are exposed to the atmosphere, weathering/erosion sucks CO2 out of the atmosphere and chills the planet. Ocean deposits of calcium carbonate (CaCO3), or limestone, indicate that CO2-rich rainwater stripped calcium from the Himalayan rock.
The research indicates that CO2 levels in the atmosphere are a major driver of Earth's climate in suggesting that atmospheric CO2 levels were dropping at the same time that the planet was getting colder.
- ScientificAmerican.com of 25 October 2006 at http://www.sciam.com/article.cfm?chanID=sa003&articleID=000CC5E6-9AB7-153F-9AB783414B7F0000&ref=rss
- ScienceDaily of 26 October 2006 at http://www.sciencedaily.com/releases/2006/10/061025185539.htm
- EurekAlert of 25 October 2006 at http://www.eurekalert.org/pub_releases/2006-10/osu-amc102306.php#