Scientists from three Dutch universities have found the first concrete evidence for the global winter that ended the age of the dinosaurs 66 million years ago.

Palaeoclimatologists at Utrecht University, VU University Amsterdam and the Royal Netherlands Institute for Sea Research have determined that the "impact winter" was caused by a huge meteorite hitting the area of present-day Mexico.

An impact winter

The Chicxulub impact, named after the village currently located at the centre of the (now buried) impact crater, led to the extinction of around half of all the plant and animal species on Earth.

When the asteroid hit the ground, it caused huge quantities of dust and aerosols to be ejected into the atmosphere, temporarily blocking the sunlight.

This caused a rapid global drop in temperature that lasted several decades, which is commonly referred to as an impact winter.

This change in the Earth’s climate ended the Cretaceous period and the existence of dinosaurs, ushering in instead the Palaeogene era.

Unearthing the evidence

While no concrete evidence of such an event had been found before, PhD student Johan Vellekoop found it in rock outcrops in Texas.

With his colleagues, Vellekoop discovered marine sediments in the rocks. These sediments had been 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," says 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."

Proving the theory

Scientists were able to determine seawater temperatures at the time of the impact by measuring certain lipids in single-cell organisms preserved in the Texan rocks. Their reconstruction shows that seawater temperature dropped at least seven degrees Celsius immediately after the impact.

"And that’s only a minimum estimate; it was probably much more," said Vellekoop. "Storms following the tsunami completely stirred the sediments up."

First solid evidence

These findings are the first concrete evidence of an impact winter following the Chicxulub impact, also known as the the K–Pg impact as it lies at the Cretaceous–Paleogene boundary.

The impact is a unique event in Earth history because not only did it cause massive climate change, followed as it was by several decades of cold and darkness, this change happened at an unparalleled rate.

The scientists propose that their detailed portrayal of the environmental consequences of the impact and its aftermath aids in understanding truly rapid climate change.

Source: University of Utrecht