Comet, Not Asteroid, Killed The Dinosaurs, Study Claims

By Pierre Dumont , Mar 23, 2013 08:52 AM EDT

The giant rock that slammed into the Yucatan Peninsula around 65 million years ago and resulted in the eventual extinction of dinosaurs was a comet, not an asteroid, scientists claim.

When the rock impacted earth, it created a 110 to 180-mile crater and resulted in the gradual elimination of over half of the species on Earth. The theory that a rock impact resulted in the mass extinction was largely agreed upon in 2010 after an international group of scientists came together to discuss the issue. They still debated, however, whether the impact was the result of a comet or an asteroid. According to new research, a comet was to blame.

The researchers came to their conclusions by studying levels of iridium, an element that could not have developed on Earth, in the crater. Their examination revealed that the rock generated less debris than thought before, indicating that it was smaller than previously believed. Given its size, the rock must have been going extremely fast to create such an impact.

 "How do we get something that has enough energy to generate that size of crater, but has much less rocky material? That brings us to comets," study author and paleoecologist at Dartmouth College Jason Moore told BBC news.

Comets are objects made of dust, ice and rocky particles and can be distinguished from asteroids by their tails, called comas, as well as their unusual orbits and thin atmospheres. If the object was in fact a comet, then much more material would have descended than from an asteroid.

There is still debate, however, given that much of the rock material could have ejected, making it impossible to find on Earth. Therefore, the traceable rock material could be just a small part of the rock itself, implying it could have still been an asteroid.

Purdue University geophysicist Jay Melosh sides with the idea that the object was a "faster-than-usual" asteroid.

"The evidence that they have for a high velocity impact is marginally positive," Melosh states. "However, the probability that that high velocity impact is a comet is very low."

The group of researchers presented their study this week at the 44th Lunar and Planetary Science Conference in The Woodlands, Texas.

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