Meteorite impact caused global darkness and cooling

Evidence for impact winter 66 Million years ago

13 May 2014

Paleoclimatologists of Utrecht University and VU University Amsterdam have found the first concrete evidence for the global cooling caused by the meteorite impact at the Cretaceous-Paleogene boundary, 66 million years ago. The results, financed by the Open programma of NWO Earth and Life Sciences, were published on the 12th of May in Proceedings of the National Academy of Sciences PNAS.

About 66 million years ago, a large meteorite impact in present-day Mexico whipped out about half of all animal and plant species on Earth. This was the end of the Dinosaurs and with it the end of the Cretaceous period. This Chicxulub impact, named after the town near its center, was the beginning of the Paleogene period, which started with a global drop in temperatures that lasted for decades.

Blocked sunlight

This impact lofted large quantities of dust and aerosols into the air, which, in turn, blocked sunlight. As a result, the earth was temporarily cloaked in darkness, which resulted in severe global cooling. This temperature drop is called an impact winter. So far however, no concrete evidence had been found that unambiguously demonstrated that this impact winter truly took place. Now, PhD-student Johan Vellekoop, from Utrecht University found the first evidence in sedimentary rocks from Texas, USA.

The right place

Together with colleagues he studied rocks from Texas that date back to the time of the impact. 'There, we studied a layer of sand and shells, deposited on the former sea floor by the tsunami caused by the impact', Vellekoop explains. 'Just above that layer is a peak in Iridium concentrations, derived from dust from the meteorite. That's how we knew we were measuring on the right spot.'

 

Yucatan chix crater  © NASAYucatan chix crater © NASA

Minimum estimate

The scientists were able to reconstruct past sea water temperatures based on microbial membrane lipids preserved in the sedimentary rocks. Their reconstruction shows that sea water cooled down with more than 7°C immediately following the impact. 'This may be a minimum estimate, as the actual cooling was probably even more', Vellekoop says. 'After the tsunami, storms have mixed sediments on the former sea floor.'

The first concrete evidence

These results are the first concrete evidence for an impact winter following the Chicxulub impact. This period of darkness and cold probably lasted for several decades and must have been one of the most important causes for the mass extinction at the end of the Cretaceous.

Publication

This publication Rapid short-term cooling following the Chicxulub impact at the Cretaceous-Paleogene boundary by Johan Vellekoop, Appy Sluijs, Jan Smit, Stefan Schouten, Johan W.H. Weijers, Jaap S. Sinninghe Damsté and Henk Brinkhuis appeared in the Proceedings of the National Academy of Sciences on May 12th, 2014.

 


Source: Utrecht University