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Continental slice

india Updated: Nov 04, 2007 21:12 IST
Prakash Chandra

Scientists are trying to solve the biggest jigsaw in the world: continents that drift. New research published in Nature explains why the subcontinent drifts the fastest, ramming into Eurasia at 20 cm per year and pushing up the Himalayas.

German scientist Alfred Wegener first proposed the theory of Continental Drift in 1912. He argued that continents once formed a single landmass, called Pangaea (Greek for ‘all land’). When lava, or molten rock, weakened Earth’s crust, this super-continent broke into pieces, which drifted into their current locations over millions of years.

On the map, you could cut out the continents and ‘fit’ them together to make a single landmass. The bulge of Africa, for instance, ‘fits’ neatly with the shape of the North American coast. So does Brazil along the African coast, beneath the bulge. Ancient mountain belts virtually line up when the continents are aligned along their coastlines. Similar plant fossils on different continents suggest their evolution on a single landmass. Antarctica, for instance, has fossils of tropical plants, indicating this frozen land was once near the Equator.

In the 1960s, scientists developed the theory of plate tectonics. According to this, continents are part of larger lithospheric ‘plates’ (rigid blocks of the planet’s surface) that include oceans and continents. When these ‘plates’ move, so do the continents and the ocean floor above them. The latest findings show that India’s lithosphere is only half as thick as others, which explains its high-speed collision with Eurasia.

There were probably several supercontinents before Pangaea, all going through a similar cycle. And it could happen again as the continents move. The Atlantic and Indian oceans are expanding, while the Pacific is shrinking. In 200 million years, people in America (if there are any) needn’t cross the Pacific to reach Asia! At the northeast corner of Africa, a new ocean is being born: the Red Sea is widening so fast that in 200 million years, it will be as big as the Atlantic is today.

Eventually, when the Mediterranean Sea disappears, Africa will be connected with Europe — like pieces of a giant jigsaw falling into place.