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.

Meert, the study leader, said the discrepancy between the new study and older ones is easy to explain: Initial age estimates were done in the early days of geochronology, when methods for dating rocks and sediments were not as accurate.

Even still, he noted, "in geology it's rare these days to revise the age of a large region of Earth by 500 million years."

Mired in Controversy

The findings have raised the ire of some researchers in India, "where the age of the basins has been sacrosanct," Meert added.

"Some Indian researchers think that we are wrong on the ages of the upper and lower sections, and [that] they both are only about 630 to 500 million years old," Meert said.

But the findings match with other recent work in the area, he added.

While his team focused on upper sedimentary sections of the basin, researchers in 2002 dated lower sediments at 1.8 to 1.5 billion years, older than the initial 1.4-billion-year age estimates, he said.

Bickford, who conducted a similar dating study in recent years in India's neighboring Chhattishgarh Basin, also found minerals dated at a billion years.

"There are a lot of implications to this," he said. "The one most exciting is the question of snowball Earth."

New Lease on Life

Supporters of the snowball Earth theory say evidence can be found in glacial etchings and sediment deposits that chart the ice flows long after it melted.

"One of the puzzling aspects of these basins, when they were thought to be younger, is that they contained no evidence of these severe glaciations," study leader Meert said. "If the rocks are as old as we think, then they should not contain glacial relics because they are too old."

Given the new age assessments, the basins would have been filled with sediment 500 million years ago, which explains the lack of glacial evidence, Bickford said.

And the new age estimates of the basins may potentially have a ripple effect on how life is believed to have developed on Earth, Meert said.

The new findings would mean that any verified fossils of multicellular organisms found in both the upper and lower sediments are older by hundreds of millions of years, he said.

Some researchers, for example, have made disputed claims about the discovery of multicellular creatures in the area dating to 1.6 billion years ago.

(Related: "Indian Fossil Bed Being Ground Into Cement" [February 6, 2008].)

If this speculation is verified, Meert said, "that would drastically impact our theories on the evolution of multicellularity."