India-Asia continental clash may have caused long term cooling in Earth's climate

Washington, Oct 11 : A new study has suggested that the collision between India and Asia set off events that likely caused long-term cooling in Earth's climate.

According to a report in Science News, the study determines that when the tectonic plate carrying India slammed into Asia about 50 million years ago, the ensuing geological changes triggered a long-term cooling trend.

That trend later enabled Antarctic ice sheets to grow.

Before the collision, volcanoes along the rim of southern Asia spewed immense quantities of carbon dioxide into the atmosphere.

Much of that planet-warming greenhouse gas came from seafloor, carbonate-rich sediments that were shoved below Asia by tectonic movements, according to Dennis V. Kent, an earth scientist at Rutgers University in Piscataway, New Jersey.

Carbon in those sediments soon reappeared in the atmosphere as the carbon dioxide spewing from volcanoes.

When the India-Asia collision removed those seafloor sediments, that source of carbon dioxide disappeared, explained Kent and his colleagues.

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 - consumed large volumes of carbon dioxide.

That double whammy, the researchers speculate, caused atmospheric concentrations of carbon dioxide to plummet, cooling Earth significantly.

About 120 million years ago, the tectonic plate that carried what is now the Indian subcontinent split from Gondwana, the supercontinent that sat astride the South Pole. The subcontinent began to move quickly northward, at times migrating about 25 centimeters per year.

By about 50 million years ago, when India crashed into Asia, atmospheric carbon dioxide levels sat well above 1,000 parts per million.

After the collision, subduction of carbonate-rich ocean crust beneath Asia ceased, so carbon dioxide levels began to drop.

Erosion of India's volcanic basalts caused carbon dioxide levels to drop even farther, the researchers propose.

When those eruptions had occurred, only 3 percent of Earth's continental land area sat between 10 degrees North and 10 degrees South.

When tectonic motions carried India into the tropics, however, that proportion rose to about 20 percent.

The high temperature and rainfall of the tropics increased erosion on the landmass, essentially soaking up large amounts of carbon dioxide from the atmosphere and cooling Earth significantly.

Between 50 million and 34 million years ago, as erosion and other geological processes sapped the greenhouse gas from the atmosphere, CO2 levels dropped to modern-day, pre-industrial levels of about 300 parts per million.

Other changes in landmass distribution in the Southern Hemisphere resulted in changes in ocean currents in the region, which led to further cooling and the development of permanent ice sheets on Antarctica.

--ANI