'Asteroid winter' killed dinosaurs 66 mln years ago

A devastating "impact winter" caused by a massive asteroid strike 66 million years ago may have wiped out the dinosaurs, a new study has found.
Researchers have discovered the first physical evidence that global temperatures suddenly plummeted following the impact off Mexico's Yucatan Peninsula.
A huge meteorite impact caused the extinction of approximately half of all the plant and animal species on Earth some 66 million years ago.
This meant not only the end of the dinosaur era, but also of the Cretaceous period.
The Chicxulub impact marked the start of the Palaeogene era and caused a global drop in temperature lasting several decades.

The impact ejected huge quantities of dust and aerosols into the atmosphere, temporarily blocking the sunlight. This caused a rapid global drop in temperature, commonly referred to as 'impact winter'.

No concrete evidence of an impact winter had previously been found, but Johan Vellekoop from the Utrecht University in the Netherlands found it in rock outcrops in Texas.
Together with his colleagues at the VU University Amsterdam and the Royal Netherlands Institute for Sea Research (NIOZ), Vellekoop discovered marine sediments in these outcrops. These sediments were laid down at the time of the meteorite impact.
"The layer of sand and shells we found was deposited by tsunamis caused by the meteorite impact," said Vellekoop.

"In the rocks just above that layer we measured high concentrations of iridium, a mineral originating from the meteorite itself. That's how we knew for sure we were looking at the right layers," said Vellekoop.
By measuring certain lipids in single-celled organisms preserved in these rocks, the scientists could determine the seawater temperature at the time. Their reconstruction shows that the seawater temperature dropped at least 7 degrees Celsius immediately after the impact.
"And that's only a minimum estimate; it was probably much more. Storms following the tsunami completely stirred the sediments up," said Vellekoop.
These findings are the first concrete evidence of an impact winter following the Chicxulub impact.

This period of cold and darkness probably lasted several decades and must have been one of the main causes of the mass extinctions at the end of the Cretaceous.
The finding was published in the journal PNAS.