Study suggests a massive comet killed dinosaurs, not an asteroid

Rick Docksai | Science Recorder | March 23, 2013

Study suggests a massive comet killed dinosaurs, not an asteroid

Did a comet kill off the dinosaurs?

The story of dinosaur extinction may be wrong, if a new scientific study of the Chicxulub crater in Mexico proves correct. The study’s authors argue that it wasn’t an asteroid that killed the dinosaurs off, but rather a comet.

The study, led by lead author Jason Moore, a paleoecologist at Dartmouth College in New Hampshire, bases its conclusions on an analysis of  series of rock collected at the Chicxulub site. Many scientists peg this 112-mile-wide crater as the site of the infamous collision from space that resulted, some 65 million years ago, in the destruction of most of the prehistoric Earth’s large reptiles and 70 percent of all animal species on the planet at the time — including the dinosaurs.

Moore and his colleagues analyzed the layers of iridium and osmium—two sediments found within the crater that could not have occurred within the rock naturally—and determined that the collision event generated less debris than scientists had previously thought. The object would therefore have been smaller than scientists had projected but going exceptionally fast.

The researchers noted that, based on the quantities of osmium and iridium, an asteroid would need to have measured three or more miles across. However, an asteroid of that size would have left a crater much smaller than 112 miles. The object that made the crater would have to have been smaller than three miles but moving at a very high speed—about 20 times as fast as a bullet, according to the team of researchers.

In all, the object’s theoretical properties more closely match a comet than an asteroid. Comets have been documented moving faster than asteroids and tend to exhibit less mass—their composite materials include ice and gas that melt away when the comets near the sun, creating the visible plumes for which comets are well known.

Comet impacts are also a much rarer occurrence than asteroids. Whereas the regions of space surrounding Earth teem with asteroids, comets are found in the solar system’s outer reaches and follow exceptionally lengthy orbits around the sun that can take thousands or even millions of years to complete. A comet striking Earth and extinguishing life would have been an extremely anomalous occurrence.

Moore and his colleagues presented their findings at the 44th Lunar and Planetary Science Conference, which convened March 18-22 in The Woodlands, Texas.

While the theory seems to have garnered a widespread consensus, they have drawn their share of challengers in the meantime. Other researchers point out that any object that falls through Earth’s atmosphere loses large quantities of matter as friction with the air burns it away. According to experts, the offending object could have plausibly been an asteroid all the same, albeit one that was reduced somewhat by the atmosphere. In other words, scientists cannot rule out a dinosaur-killing, faster-than-average asteroid just yet.


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