olelog

There is no doubt that plate tectonics have an influence on the global climate.
A change in global temperature of a few degrees Celsius over 50 years is dramatic. A change in global temperature of a few degrees Celsius over 5 000 000 years is NOT, you just cannot compare two trends on such extremely different time scales - a fact that some people seem to ignore.

About 90-70 million years ago India had split from the supercontinent Gondwana and raced northwards, sometimes at the incredible speed of 25 cm per year, until it rammed into Asia about 40 to 50 million years ago. Before the collision it was hot on earth, partly because volcanoes at the sea bottom released enormous quantities of the greenhouse gas CO₂ into the atmosphere. The Cretaceous (145 million to 65 million years ago) was one long heat wave. Average annual temperatures at the equator topped 38°C and even polar temperatures hovered near a temperate 10°C.

Some of the undersea volcanism came to an end at the collision of India against Asia, and erosion of uplifted volcanic rocks in the tropics soaked up much of the CO₂. This led to a cooling of the global climate that lasted until about 34 million years ago. A cooling that together with changes in the ocean circulation initiated the covering of Antarctica with ice.

Fact or fantasy? Fact seems to be that increases in atmospheric CO₂ contributed to a warm spell 50 million years ago called the Early Eocene climate optimum – the warmest period in the 65 million years since the Cretaceous. But over the following 15 million years, deep sea temperatures fell by about 12°C, reflecting a significant cooling at the surface. This cooling ultimately allowed the cycle of ice ages to emerge.

According to a paper in PNAS atmospheric CO₂ levels sat well above 1,000 parts per million by about 50 million years ago, when India crashed into Asia. But after the collision, seafloor sediments were no longer a volcanic source of carbon (C), so levels began to drop. Simultaneously, erosion of rocks on the Indian subcontinent - in particular, the chemical weathering of a large amount of basaltic rocks formed from volcanic eruptions just a few million years earlier (the Deccan traps that formed about 65 million years ago) - consumed large volumes of CO₂. When the volcanic basalts formed, only 3 percent of Earth's continental land area sat within 10 degrees of the equator. But as tectonic motions carried India into the tropics and shifted other land masses, that proportion increased to about 20 percent. The high temperature and rainfall of the tropics increased erosion on the landmass, essentially soaking up large amounts of CO₂ from the atmosphere.

Scientists do not quite agree on exactly how the planet got so warm in the Cretaceous. It is indeed something that they have struggled to explain. Here is a view published in Geotimes in April 2008: A slight reduction in cloud cover that allowed more sunlight to reach Earth could have been the necessary nudge needed to push the planet into a "supergreenhouse" world. - Blue skies!

• http://www.pnas.org/content/105/42/16065
• http://www.articlearchives.com/north-america/united-states-northeast-usa-new-york/2179279-1.html
• http://features.csmonitor.com/innovation/2008/09/25/warming-in-a-global-cool-period/
• http://www.geotimes.org/apr08/article.html?id=WebExtra041008.html

I thought it appropriate that my first post after the terrible tragedy in Mumbai, for which I have no words, nevertheless should contain words like Mumbai, India and Deccan (with Deccan Mujahideen in mind).

I fight with my pen - sorry keyboard. Knowledge is a life saver.

An “eye for eye” only ends up making the whole world blind.