Magazine article Science News

Continental Clash Cooled Climate: When India and Asia Collided, Sources of C[O.Sub.2] Disappeared

Magazine article Science News

Continental Clash Cooled Climate: When India and Asia Collided, Sources of C[O.Sub.2] Disappeared

Article excerpt

When the tectonic plate carrying India slammed into Asia about 50 million years ago, the ensuing geological changes triggered a long-term cooling trend--a trend that later enabled Antarctic ice sheets to grow, a new study suggests.

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 being shoved below Asia by tectonic movements, says Dennis V. Kent, an earth scientist at Rutgers University in Piscataway, N.J.

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

Before India reached the tropics, a spate of volcanic activity lasting a million years spewed about 4 million cubic kilometers of basalt lava--an outpouring that contributed to the demise of the dinosaurs, some scientists propose.

By about 50 million years ago, when India crashed into Asia, atmospheric C[O.sub.2] levels sat well above 1,000 parts per million. But after the collision, seafloor sediments were no longer a volcanic source of C[O.sub.2], so levels began to drop, Kent and his colleagues argue in a paper published online September 22 in the Proceedings of the National Academy of Sciences.

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 C[O.sub.2].

When the volcanic basalts formed, only 3 percent of Earth's continental land area sat within 10 degrees of the equator. …

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