Washington, July 4 : Geologists have found strong evidence that a half-dozen major basins that are located south of New Delhi in India were formed a billion or more years ago, making them at least 500 million years older than commonly thought.
The Purana basins - which include the subject of the study, the Vindhyan basin - are located south of New Delhi in the northern and central regions of India. They are slight, mostly flat depressions in the Earth's crust that span thousands of square miles.
According to Joe Meert, a UF (University of Florida) associate professor of geology, for decades, most geologists have believed the basins formed 500 million to 700 million years ago when the Earth's crust stretched, thinned and then subsided.
"In modern geology, to revise the age of basins like this by 500 million years is pretty unique," said Meert.
"The required revision is enormous - 500 million years or about 11 percent of total Earth history," said Abhijit Basu, a professor of geological studies at Indiana University.
Meert said that the date may have originated in early radiometric dating of sediment from the basin. Radiometric dating involves estimating age based on the decay or radioactive elements.
Additionally, he said, apparent fossils retrieved from the basin seemed to have originated between 500 million and 700 million years ago.
The researchers were working on an unrelated project when a UF graduate student, Laura Gregory, dated a kimberlite retrieved from the Vindhyan basin to about 1,073 million years ago.
A kimberlite is a volcanic rock that contains diamonds.
Gregory also used paleomagnetism, a technique that estimates where rocks were formed by using the orientation of their magnetic minerals.
Curious about whether the kimberlite results would apply more generally to the region, fellow UF graduate student Shawn Malone compared the kimberlite's orientation to other rocks from the Vindhyan basin.
To his surprise, he found the orientations were virtually identical.
As a result, the geologists expanded the investigation, using a modified chain saw to drill wine-cork-sized cores out of dozens of rocks collected from 56 sites.
"Their contents all also had the same or very similar magnetic orientation," said Meert.
Much of the basins are composed of sediments that cannot be dated using any method. But, according to Meert, the sediment also contains zircon, which can be dated using laser mass spectrometry.
"All the zircon the researchers tested originated 1,020 million years ago," said Meert.
The findings appear to remove one of the major obstacles to the Snowball Earth theory that a frozen Earth was once entirely covered in snow and ice - and might even lend some weight to a controversial claim that complex life originated hundreds of million years earlier than most scientists currently believe.