Blocking the sun
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 PhD student Johan Vellekoop (Utrecht University) found it in rock outcrops in Texas.

Right spot
Together with his colleagues, he 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”, 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.”

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°C immediately after the impact. “And that’s only a minimum estimate; it was probably much more”, says Vellekoop. “Storms following the tsunami completely stirred the sediments up.”