The last day of the dinosaurs: “They were charred and then frozen”


65 million years ago, a massive ten-kilometer rock hit Earth, triggering the fifth mass extinction . It was, then, the last day of the dinosaurs and the first of a new era dominated by mammals and man. Little was known of what happened at that time … until now. And it is that those 24 hours have been reconstructed minute by minute in a study published by the magazine Pnas. 

The research, led by scientists from the Institute of Geophysics of the University of Texas (United States), is based on the analysis of rock samples extracted from the “ground zero” of the impact, the Chicxulub crater, in the Yucatan peninsula ( Mexico).

The study, in which researchers from the Center for Astrobiology (CSIC-INTA) have participated, reconstructs the geological , chemical and biological processes generated by the impact of the asteroid that fell on Earth with a power equivalent to ten billion atomic bombs such as Hiroshima’s.

At first, the explosion burned the vegetation that was several thousand kilometers around and triggered a giant tsunami that swept sediments into the interior of North America – more than 2,000 kilometers inland – but the worst came later.

The impact killed 75% of life on the planet

The impact released so much sulfur into the atmosphere that it blocked sunlight and caused global cooling that wiped out dinosaurs and 75 percent of the planet’s life forms.

It was a short-lived local hell , followed by a long period of global cooling: the dinosaurs ” burned and then froze, ” though “not all died that day.” This is summarized by Sean Gulick, a research professor at the University of Texas Institute of Geophysics and lead author of the study.

Analyzes indicate that most of the material that filled the crater in the hours after impact originated from the same impact site or was carried by ocean water that flowed back into the crater from the surrounding Gulf of Mexico.

About 130 meters of material were deposited in a single day , a vertiginous accumulation rate that is among the highest ever found in the geological record and that has allowed the reconstruction of events that took place inside and outside the crater from the moment of impact until several hours later.

Jens Ormö, a researcher at the Center for Astrobiology and co-author of the study, analyzed the samples to try to determine how the accumulated material had been transported and deposited at the impact site – and sometimes also where it came from – something essential to understand the amount of water that was flowing in the crater and the processes that happened when it was filling up.

Sulfur was “the real killer”

“The sediments reveal enormous transport energies that are much larger than any other known catastrophic flood on the planet. Dense, debris-filled water moved at speeds that were equal to the wind speed of hurricanes, ” Ormö says.

But perhaps the most important research finding is related to sulfur, the chemical element that caused global cooling and climate change that caused the mass extinction ; “the real killer,” according to Gulick.

Analysis of the rock samples reveals that the asteroid’s impact vaporized at least 325 billion metric tons of sulfur-rich minerals present at the impact site, enough to cause sunlight to become opaque and cause drastic cooling. on the whole Earth.

The amount of sulfur released into the atmosphere that day is about 10,000 times greater than that expelled by the Indonesian Krakatoa volcano in 1883 , which caused an average drop of 2.2 degrees in global temperature for five years.

For Ormö, “everything that can be deduced from the sediments deposited in those first moments allows us to know what the first day of the Cenozoic was like, the first day of a new era dominated by mammals and eventually by our own species. A species that Now, for other reasons such as massive pollution of the oceans and the atmosphere, the sixth and last of the mass extinctions has begun. Perhaps we are still in time to learn something from the past


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