It was the Asteroid!

The jury’s finally back: it was indeed an asteroid that killed the dinosaurs.

How the dinosaurs went extinct 65 million years at the end of the Cretaceous period has been up to debate for decades, though many paleontologists agreed that a massive asteroid impact could have done it. Alternate theories were climate change, plant evolution, volcanic activity, disease, and mammals evolving fast enough to be a threat to the dinosaurs.

The asteroid theory held the most plausibility of all the theories—and was the most widely accepted—because of evidence that showed that there was such an event around 65 million years ago. On the Yucatan Peninsula in Mexico, there’s the Chicxulub crater, which is at least 110 miles wide, meaning the asteroid that did the deed had to be greater than six miles long.

What paleontologists have found and used for evidence that the Chicxulub impact was the cause for the extinction was the KT boundary. The layer of sediment from 65 million years ago—coinciding with the impact and the extinction—contains an astronomically high level of iridium, a heavy metallic element that is rarely found on Earth, but commonly in asteroids. Luis Alvarez and his son Walter found the KT boundary and created the theory in 1980 that an asteroid caused the extinction.

About 40 scientists from around the world met to discuss the event. They published an article in Science on Thursday stating that it was the asteroid at Chicxulub that caused the massive extinction. The Yucatan region was already sulfur-rich, and the impact kicked billions of tons of the element into the atmosphere. That along with other debris from impact blocked out the sun and killed off plant life. The shockwave knocked down trees, and the heat of the asteroid entering the atmosphere set forests on fire even before impact. The resulting explosion was a billion times more powerful than the bomb that was dropped on Hiroshima, Japan.

The fact that any life could survive this event seems miraculous. Mammals at the time were more like mice and shrews than anything big enough to be of any concern to a dinosaur, so having a much smaller need for food and being able to hide underground allowed our ancestors to live long enough to claim the Earth in their name in later geologic periods.

For more information:

http://www.csmonitor.com/From-the-news-wires/2010/0309/What-s-to-blame-for-dinosaur-extinction-Asteroids

http://www.washingtonpost.com/wp-dyn/content/article/2010/03/09/AR2010030903428.html

http://en.wikipedia.org/wiki/Kt_boundary

http://en.wikipedia.org/wiki/Chicxulub_crater