Scientists Reconstruct What Happened The Day The Dinosaurs Died

Sixty-six million years ago, an asteroid blast the equivalent of 10 billion World War II atomic bombs set off wildfires, triggered tsunamis and emitting enough sulfur into the atmosphere to block out the sun. The result? A mass extinction that killed off 75 percent of life on Earth, including all nonavian dinosaurs. AuntSpray/Shutterstock

Sixty-six million years ago, an asteroid blast the equivalent of 10 billion World War II atomic bombs set off wildfires, triggered tsunamis, and emitted enough sulfur into the atmosphere to block out the Sun. The result? A mass extinction that killed off 75 percent of life on Earth, including all nonavian dinosaurs.

At least, that’s been the longstanding, yet often contested theory. Now, new research published in Proceedings of the National Academy of Sciences confirms the theory and provides an “unprecedented window” into the immediate aftermath of the impact.

An international team of more than two dozen scientists analyzed core samples from rocks within the mountains and hills surrounding the Chixculub cater in the Yucatan Peninsula, a massive hole measuring nearly 30 kilometers (19 miles) deep and 193 kilometers (120 miles) wide. Within minutes of the asteroid’s impact, “fluidized basement rocks” formed a ring of hills around the crater. Within hours, ocean waters flooded the crater and deposited an estimated 90 meters (295 feet) of rock into its base. Within one day, 130 meters (425 feet) of material was deposited within the crater – among the highest in the geological record. By the next day, a tsunami had left material from distant shorelines that included the remnants of charcoal.

The charcoal here is key. Scientists say they can use its presence as a “chemical biomarker” that suggests wildfires ignited by the impact burned trees and plants thousands of miles away. Within charcoal samples were indicators of soil fungi present in sand, suggesting the charcoal was pushed into the crater by receding tsunami waters.

A portion of the drilled cores from the rocks that filled the crater. 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 the impact vaporized these rocks, forming sulfate aerosols in the atmosphere and causing cooling on a global scale. Credit: International Ocean Discovery Program.

“It’s an expanded record of events that we were able to recover from within ground zero,” said study author Sean Gulick, a research professor at the University of Texas Institute for Geophysics, in a statement. “It tells us about impact processes from an eyewitness location.”

Here’s where it gets interesting. The area around the crater is full of sulfur-rich rocks, and yet no sulfur was found within the core samples. This may be explained by the asteroid’s ability to vaporize any minerals that might have held sulfur, thereby releasing an estimated 225 billion metric tons of sulfur into the atmosphere. As the mineral reflected the Sun away from the Earth, global cooling would have ensued to pave the way for mass extinction.

“The real killer has got to be atmospheric,” said Gulick. “The only way you get a global mass extinction like this is an atmospheric effect.”

The study builds on previous research that explains how the crater was formed and validates the notion that the asteroid’s impact caused the planet’s surface to behave like a fluid, creating the mountains and hills that surround the crater from rocks that came from deep within the Earth’s crust.

“We fried them and then we froze them,” Gulick said. “Not all the dinosaurs died that day, but many dinosaurs did.”

Interestingly, life quickly recovered at the site. Less than a decade after the impact, researchers discovered that the crater quickly became home to sea life and thrived as a marine ecosystem for the next 30,000 years.

An animation showing the impact and subsequent crater formation (University of Arizona, Space Imagery Center)

 

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