When the volcano Toba erupted on Sumatra 73,000 years ago, the blast was so powerful that a curtain of ash blocked solar radiation for six years and plunged the world into an 1,800-year ice age that saw temperatures plummet as much as 28 degrees Fahrenheit.

Now, a new study from the University of Illinois at Urbana-Champaign shows the eruption caused even more chaos: It deforested much of central India, some 3,000 miles away from the blast's epicenter.

Stanley Ambrose, a University of Illinois anthropology professor, has been studying the Toba eruption for more than a decade.

In 1998, he proposed that the effects of the volcano blast and ensuing "Instant Ice Age" could explain the apparent bottleneck in human populations that scientists believe happened 50,000 and 100,000 years ago.

When Toba erupted, the volcano covered the entire Indian subcontinent with about 6 inches of ash. Today that ash continues to be found in India, the Indian Ocean, the Bay of Bengal and the South China Sea.

To better understand the eruption's massive devastation, Ambrose teamed up with Martin A.J. Williams, a University of Adelaide environmental studies professor who discovered Toba ash in 1980, to gauge the terrestrial impact.

First, they looked at pollen trapped below the floor of the Bay of Bengal where ash from the Toba eruption was deposited.

Then they analyzed carbon isotopes from soil taken above and below the Toba ash in three locations in central India in hopes of determining the kind of vegetation that existed at the time. Certain carbon isotopes reflect the type of vegetation that existed at a given location at a specific time.

What they found was a distinct change in vegetation after the Toba eruption, according to their study published in the journal Paleogeography, Paleoclimatology and Paleoecology.

The pollen analysis showed a more open vegetation and cover and the widespread loss of ferns, which grow best in humid conditions. The loss of ferns, the researchers wrote, "would suggest significantly drier conditions in this region for at least 1,000 years after the Toba eruption."

The isotope analysis revealed that forests covered central India when Toba erupted, but wooded to open grasslands took over for at least 1,000 years after that.

"This is unambiguous evidence that Toba caused deforestation in the tropics for a long time," Ambrose said.