Asteroid that killed dinosaurs 66 million years ago ‘also cooled earth’

PUBLISHED : Wednesday, 14 May, 2014, 9:14pm
UPDATED : Wednesday, 14 May, 2014, 9:15pm


The asteroid that wiped out the dinosaurs also caused a temporary but devastating "impact winter" - darkening the sky, cooling the earth and inhibiting photosynthesis, new research suggests.

Some 66 million years ago, a 10km-wide asteroid known as Chicxulub struck the earth off the Yucatan coast in Mexico, setting off a series of catastrophic events that led to one of the world's worst mass extinctions.

Computer simulations suggest that in the hours immediately after the impact, life on earth was rattled by massive earthquakes and tsunamis, as well as global wildfires.

Then, dust and soot rose into the atmosphere, absorbing sunlight and keeping it from reaching the earth's surface. Plants had trouble getting enough light to photosynthesise, causing a wide-scale collapse of the food web. At the same time, the surface of the planet began to cool.

The impact winter did not last long, however. Over a few months or possibly a few decades, the dust and soot fell out of the atmosphere and rained down onto the land and oceans, allowing sunlight to warm the planet once again.

It's a compelling story, but one that has been difficult to prove - until now. Writing in the Proceedings of the National Academy of Sciences, a team of scientists from the Netherlands say they have found the first hard evidence of the impact winter, buried deep in the geological record.

To take the temperature of the earth 66 million years ago, the researchers looked at lipids produced by an ocean-dwelling micro-organism called Thaumarchaeota, preserved in sedimentary rocks near the Brazos River in the US state of Texas.

Back in the Cretaceous period this site was covered by a warm sea, said Johan Vellekoop of Utrecht University in the Netherlands and the lead author of the paper.

When the giant asteroid hit, a tsunami rolled over the site and covered it with a series of sandy layers. On top of that, the researchers found a thin layer of sediment that is more fine at the top than at the bottom, and it is in this layer that they found lipid evidence of a major cooling.