“It would have felt like the ground beneath your feet had become a ship in the middle of the ocean,” says earth and space science professor Mark Richards at the University of Washington. “Then rocks would have bombarded you from a boiling sky that was beginning to take on a hazy glow. Massive wildfires would have sprouted up as the ground burst into flames. It would have seemed like the end of the world.”
On November 21, 2018 in “Dinosaurs On the Moon” — The Impossible Magnitude-12 Earthquake That Changed Our World, The Daily Galaxy reported that the asteroid itself was so large that, even at the moment of impact, the top of it might have still towered more than a mile above the cruising altitude of a 747, writes author Peter Brannen in Ends of the World. “In its nearly instantaneous descent, it compressed the air below it so violently that it briefly became several times hotter than the surface of the sun.”
The atmosphere didn’t even make a scratch on it
“The pressure of the atmosphere in front of the asteroid started excavating the crater before it even got there,” geophysicist Mario Rebolledo at the Centro de Investigación Científica de Yucatán, told Brannen. “Then, when the meteorite touched ground zero, it was totally intact. It was so massive that the atmosphere didn’t even make a scratch on it.”
In the Yucatán, Rebolledo continues, “it would have been a pleasant day one second and the world was already over by the next. As the asteroid collided with the earth, in the sky above it where there should have been air, the rock had punched a hole of outer space vacuum in the atmosphere. As the heavens rushed in to close this hole, enormous volumes of earth were expelled into orbit and beyond—all within a second or two of impact.”
That’s the scenario scientists have painted. Now, a new study led by The University of Texas at Austin has confirmed it by finding hard evidence in the hundreds of feet of rocks that filled the impact crater within the first 24 hours after impact.
The evidence includes bits of charcoal, jumbles of rock brought in by the tsunami’s backflow and conspicuously absent sulfur. They are all part of a rock record that offers the most detailed look yet into the aftermath of the catastrophe that ended the Age of Dinosaurs, said Sean Gulick, a research professor at the University of Texas Institute for Geophysics (UTIG) at the Jackson School of Geosciences.
“It’s an expanded record of events that we were able to recover from within ground zero,” said Gulick, who led the study and co-led the 2016 International Ocean Discovery Program scientific drilling mission that retrieved the rocks from the impact site offshore of the Yucatan Peninsula. “It tells us about impact processes from an eyewitness location.”
The NASA image below shows an artist’s interpretation of the asteroid impact. The asteroid in the artwork appears much larger than the six-mile rock that scientists hypothesize actually struck the Earth 66 million years ago. Nevertheless, the image nicely illuminates the heat generated as the asteroid rapidly compresses upon impact and the vacuum in its wake. (Don Davis)
The research was published in the Proceedings of the National Academy of Sciences on Sept. 9 and builds on earlier work co-led and led by the Jackson School that described how the crater formed and how life quickly recovered at the impact site. An international team of more than two dozen scientists contributed to this study.
When they examined a portion of the drilled cores from the rocks that filled the crater left by the asteroid impact that wiped out the dinosaurs. Scientists found melted and broken rocks such as sandstone, limestone and granite — but no sulfur-bearing minerals, despite the area’s high concentration of sulfur containing rocks. This finding suggests that the impact vaporized these rocks forming sulfate aerosols in the atmosphere, causing cooling on the global scale.
Most of the material that filled the crater within hours of impact was produced at the impact site or was swept in by seawater pouring back into the crater from the surrounding Gulf of Mexico. Just one day deposited about 425 feet of material—a rate that’s among the highest ever encountered in the geologic record. This breakneck rate of accumulation means that the rocks record what was happening in the environment within and around the crater in the minutes and hours after impact and give clues about the longer-lasting effects of the impact that wiped out 75% of life on the planet.
A Short-lived inferno followed by a long period of global cooling
Gulick described it as a short-lived inferno at the regional level, followed by a long period of global cooling. “We fried them and then we froze them,” Gulick said. “Not all the dinosaurs died that day, but many dinosaurs did.”
Researchers estimate the asteroid hit with the equivalent power of 10 billion atomic bombs of the size used in World War II. The blast ignited trees and plants that were thousands of miles away and triggered a massive tsunami that reached as far inland as Illinois. Inside the crater, researchers found charcoal and a chemical biomarker associated with soil fungi within or just above layers of sand that shows signs of being deposited by resurging waters. This suggests that the charred landscape was pulled into the crater with the receding waters of the tsunami.
Jay Melosh, a Purdue University professor and expert on impact cratering, said that finding evidence for wildfire helps scientists know that their understanding of the asteroid impact is on the right track.
“It was a momentous day in the history of life, and this is a very clear documentation of what happened at ground zero,” said Melosh, who was not involved with this study.
However, one of the most important takeaways from the research is what was missing from the core samples. The area surrounding the impact crater is full of sulfur-rich rocks. But there was no sulfur in the core.
That finding supports a theory that the asteroid impact vaporized the sulfur-bearing minerals present at the impact site and released it into the atmosphere, where it wreaked havoc on the Earth’s climate, reflecting sunlight away from the planet and causing global cooling. Researchers estimate that at least 325 billion metric tons would have been released by the impact. To put that in perspective, that’s about four orders of magnitude greater than the sulfur that was spewed during the 1883 eruption of Krakatoa—which cooled the Earth’s climate by an average of 2.2 degrees Fahrenheit for five years.
Although the asteroid impact created mass destruction at the regional level, it was this global climate change that caused a mass extinction, killing off the dinosaurs along with most other life on the planet at the time.
“The real killer has got to be atmospheric,” Gulick said. “The only way you get a global mass extinction like this is an atmospheric effect.”
The Daily Galaxy, Chris Anderson, via University of Texas at Austin
Image credit top of page: BBC Day the Dinosaurs Died