India Basins Half a Billion Years Older Than Thought

Kimberly Johnson
for National Geographic News
July 10, 2008

India's Vindhyan Basins have hidden their age well—by as much as 500 million years, according to controversial new research.

The basins, which stretch across a 39,000-square-mile (100,000-square-kilometer) swath of central India, were initially believed to have formed about 500 to 700 million years ago after Earth's crust stretched, thinned, and then faulted.

Six of the basins studied, however, show evidence that they were created a billion years ago, said study lead author Joseph Meert, a geology professor at the University of Florida.

The drastic age revision offers new evidence for the "snowball Earth" hypothesis, which says that Earth's surface was completely covered with snow and ice about 700 million years ago, according to the scientists.

It may also lend some support to claims that multicellular organisms found in the region date to 1.6 billion years ago, several hundred million years before most scientists believe such creatures developed.

The study appears in a recent issue of the journal Precambrian Research.

Rock-Solid Evidence

The team made their new age assessment after stumbling across kimberlite—a type of volcanic mineral often laced with diamonds—in vertical channels running down into Earth's mantle.

Researchers dated the kimberlite to about 1.073 billion years ago using radioactive decay.

The scientists also documented the rocks' magnetic orientation, since rocks containing magnetic, iron-bearing minerals typically orient themselves with Earth's magnetic poles as they crystallize.

"If you look at old rocks, the pole position can be all over the place—not because the pole has moved but because the rocks have moved," said Syracuse University geology professor M.E. Bickford, who was not affiliated with the new study.

The magnetic orientations of rocks from 56 other sites scattered throughout the basin were consistent with the kimberlite, the researchers found.

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