March 24, 2013
New Theory Suggests That A Comet Was The Culprit Behind Chicxulub Dinosaur Extinction
Brett Smith for redOrbit.com - Your Universe Online
One of the most popular theories on the disappearance of the dinosaurs surrounds the 110 mile-wide Chicxulub crater in Mexico. Many scientists believe the extinction was caused by an asteroid that crashed into Earth, leaving only a massive crater behind.However, a group of American scientists is presenting a theory that the culprit was actually a speeding comet, not a relatively slow-moving asteroid as many theories assert.
According to Jason Moore from Dartmouth College, who presented a study at the 44th Lunar and Planetary Science Conference, evidence from the crater suggests there are possibilities beyond an asteroid impact.
"The overall aim of our project is to better characterize the impactor that produced the crater in the Yucatan peninsula [in Mexico]," Moore told BBC News.
After analyzing the distribution of iridium and osmium that was globally deposited by the impact, the team determined the collision left less debris than previously calculated. This led the team to believe the impact was caused by a relatively smaller object than previously thought.
"You'd need an asteroid of about 5km diameter to contribute that much iridium and osmium. But an asteroid that size would not make a 200km-diameter crater," Moore said. "So we said: 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."
Gareth Collins, who researches impact craters at Imperial College London, told the BBC that the Dartmouth study was "thought-provoking". However, he disagreed with the American team´s conclusion.
"I don't think it is possible to accurately determine the impactor size from geochemistry,” he said. "Geochemistry tells you - quite accurately - only the mass of meteoritic material that is distributed globally, not the total mass of the impactor.
“To estimate the latter, one needs to know what fraction of the impactor was distributed globally, as opposed to being ejected to space or landing close to the crater,” Collins noted. "The authors suggest that 75 percent of the impactor mass is distributed globally, and hence arrive at quite a small-sized impactor, but in reality this fraction could be lower than 20 percent.”
Comets are thought to originate from just outside the solar system. They follow highly elliptical orbits that pass the sun. Some scientists believe gravitational forces from the outer planets or passing stars occasionally send the icy rocks hurtling towards the inner Solar System at high speeds.
If a comet did cause the impact at Chicxulub, it would have set off an enormous shockwave that would trigger gigantic tsunamis, earthquakes, and volcanic eruptions. The impact would have also sent a cloud of super-heated dust into the atmosphere, blocking out the sun and sending global temperatures plummeting. This chain of events would have likely spelled the end of the dinosaurs rule on Earth.
A massive impact isn´t the only major theory surrounding the extinction of the massive creatures. redOrbit recently reported scientists have also suggested a high level of volcanic activity could have produced the same results as a large asteroid or comet striking the Earth.