Science Team says Giant Meteorite, not Volcanoes, Killed Dinosaurs

A team of scientists, including Elisabetta Pierazzo, a senior scientist at the Tucson-based Planetary Science Institute, has concluded that a giant meteorite impact is still the best explanation for the disappearance of dinosaurs and many other species 65.5 million years ago.

The 41 scientists, from Europe, Mexico, Canada, Japan and the United States, published their results today in the highly respected scientific journal Science, concluding that alternative hypotheses are inadequate in explaining the abrupt mass extinction at the end of the Cretaceous period.

Scientists refer to this point in the geologic record as the K/Pg boundary, and attribute it to extreme climate change caused by the Chicxulub (Chick-shuh-loob) meteorite impact.

Pierazzo, who began modeling the impact as a Ph.D. student, was the first scientist to develop high-resolution, 3-D simulations of the Chicxulub event as an oblique impact. This work was done in collaboration with David Crawford, of Sandia National Laboratory. The results clearly showed that the effects on Earth’s climate were even more dramatic than had been previously hypothesized. The simulation showed huge amounts of sulfur oxides were ejected into the upper atmosphere, drastically altering the Earth’s climate.

However, some scientists have disputed the Chicxulub hypothesis, attributing the climate change and mass extinctions to volcanic activity in the Deccan Traps, an area on the Indian subcontinent. They theorize that global cooling and acid rain resulting from this volcanic activity were the major cause of mass extinctions, not the Chicxulub impact in Mexico.

“Large amounts of sulfur oxides were injected into the atmosphere during the Deccan volcanism,” Pierazzo said. “But they were distributed in several pulses that extended over several hundred thousand years before – and after – the K/Pg boundary. Yet, the major, large biotic changes at the end of the Cretaceous era appear to have happened abruptly and exactly at the K/Pg boundary, when Chicxulub hit.”

Marine and terrestrial ecosystems showed only minor changes during the 500,000 years leading up to the K/Pg boundary, the researchers conclude in the Science article. But an abrupt and major decrease in the mass of living things and species diversity occurs precisely at the boundary.

This data, along with new data derived from ocean drilling samples and continental sites, as well as reanalysis of previous K/Pg boundary studies, leads the research team to conclude that the Chicxulub impact hypothesis has grown stronger than ever.

“Combining all available data from different science disciplines led us to conclude that a large asteroid impact 65 million years ago in modern-day Mexico was the major cause of the mass extinctions,” says Peter Schulte, assistant professor at the University of Erlangen in Germany and lead author of the review paper.

According to analysis of the Chicxulub crater in Yucatan, Mexico and other data from the geologic record, scientists conclude that the meteorite was between 10 and 15 kilometers in diameter and hit Earth at a speed 20 times faster than a rifle bullet. The resulting explosion was a billion times larger than the Hiroshima atomic bomb and a million times larger than the biggest nuclear bomb ever tested.

Ed Stiles, Planetary Science Institute

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