for National Geographic News
The thinness of the Indian continent allowed it to speed northward at ten times the rate of other tectonic plates, a new study suggests.
The oldest parts of India are about a half to a third as deep as similarly old portions of Australia, Africa, and Antarctica, geophysicists measured using a new technique.
This allowed India to far outstrip the speed of the other sluggish and thicker tectonic plates, also known as lithosphere, after the breakup of a massive supercontinent 150 million years ago.
"The Indian lithosphere is only 62 miles [100 kilometers] thick, whereas the African, Australia, and Antarctica lithospheres are 124 miles [200 kilometers] or more," said Rainer Kind, one of the study's authors.
"India was able to move faster and farther because it was much thinner. If it is thinner, it's easier to push away—the resistance is less," added Kind, who is a geophysicist at the Geoforschugsventrum in Potsdam, Germany, and the Freie Universität in Berlin.
The new study appears in this week's issue of the journal Nature.
Tracking the Continents
Earth is covered by several major continental plates, which have jostled around its surface for billions of years. Their movements shift the world's oceans and land masses around at a snail's pace—but one that adds up over enough time.
(Related: "Oldest Known Ocean Crust Found on Greenland" [March 22, 2007].)
"From mapping both the gravity and magnetic field of the ocean, we can then [reconstruct] the relative motions between plates," said Dietmar Müller, an earth scientist at the University of Sydney, Australia, who was not involved in the study.
"Paths of the individual tectonic plates are frozen into the ocean floor a little bit like railroad tracks, and we can see these tracks in the ocean's gravity field."
Geologists can also study rock samples to map the path of a continent relative to the magnetic poles through time.
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