It has been known for years that the Deccan Traps, an area of volcanic rock in central India, was an active volcano around 65 million years ago. It has even been suggested that it was massive volcanic eruptions from that region that killed the dinosaurs, rather than an asteroid impact. A new study indicates that environmental changes had already been causing mass extinctions on the ocean floor at the time the asteroid hit Mexico's Yucatán Peninsula.
A research team from the University of Washington examined sediment and fossils from Seymour Island, off the Antarctic Peninsula, using a method called magnetostratigraphy — comparing the magnetic polarity of the sediment to known changes in Earth's magnetic field over time. The unusually thick layers of sediment on Seymour Island gave the researchers better accuracy in their estimates of when the layers, and any fossils in the layers, were deposited.
"The eruptions started 300,000 to 200,000 years before the [asteroid] impact, and they may have lasted 100,000 years," said UW doctoral student Thomas Tobin, who was on the research team.
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They also discovered another mass extinction that coincided with that time period. Along with volcanic dust, the eruptions spewed out tons of carbon dioxide, methane and water vapour — greenhouse gases that warmed the planet and caused a die-off of clam and snail species on the ocean floor. Of course, there may have been other species that died off during that same time and for the same reason, but clams and snails left behind the most obvious evidence — their shells.
The study found no evidence that this first extinction event had any direct effect on extinctions caused by the asteroid impact. However, Tobin speculates that it's possible some species that may have been able to survive after the asteroid impact may still have died off due to being weakened by the environmental after-effects of the Deccan Traps eruptions.
"It seems improbable to me that they are completely independent events," he said.