Ancient Indian basin beat the cold

By , Staff Writer for The Christian Science Monitor

Scientists in the US and India appear to have kicked back the age of a prominent feature in India – the Vindhyan Basin – by half a billion years. In the process, they may have removed one of the stumbling blocks to the so-called “snowball Earth” theory. The theory posits that Earth’s surface was covered pole to pole with ice on and off between 635 million and 700 million years ago. At the least, the team says, the new results give a better sense of India’s relative position as the supercontinent Gondwana formed.

Initial estimates of the basin’s age ranged from 500 million to 700 million years old, forming as the crust thinned, then subsided. But the team analyzed tiny zircon crystals in the basin’s sediments, which yielded dates for the basin’s formation some 1.02 billion years ago. In addition, they used paleomagnetic information gleaned from samples of kimberlite, a volcanic, diamond-bearing rock, to reconstruct the Indian continent’s migration at the time.

As for snowball Earth, one criticism of the theory – based on the old dates – holds that the Vindhyan Basin lacks the physical evidence for the presence of ancient glaciers, such as boulder beds with striated pebbles, or changes in the type of carbon found in rocks. But the new age for the basin explains that lack of evidence, the team holds, because the subsurface rocks that comprise it had been deposited and covered long before Earth froze over.

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The results appear in the current issue of the journal Precambrian Research.

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