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Sixty-six million years ago, the story of life on Earth changed dramatically when an asteroid slammed into what is now the Yucatán Peninsula at Chicxulub, Mexico. The aftermath of the impact wiped out an estimated 75 percent of animal species, including most of the dinosaurs except for birds. But almost nothing remained of the asteroid itself.
In a new study published Thursday in the journal sciencesResearchers have identified the chemical identity of the asteroid that caused the planet’s fifth mass extinction. The findings suggest the dinosaur killer was a clay-rich mud ball containing material from the dawn of the solar system.
Although the Chicxulub asteroid landed on Earth tens of millions of years ago, identifying this ancient space rock is important because it is “part of a bigger picture of understanding the dynamic nature of our solar system,” said Dr. Steven Godris, a research professor of chemistry at Vrije Universiteit Brussel and co-author of the study.
In 1980, scientists hypothesized that Collision with a giant space rock resulted in At the time, researchers didn’t find the asteroid itself; instead, they found a thin layer of the mineral iridium in rocks around the world dating back 66 million years. Iridium is rare in Earth’s crust but abundant in some asteroids and meteorites.
Some members of the wider scientific community were skeptical of this hypothesis. However, in 1991, scientists found that the Chicxulub crater was the right age to have been formed by a massive asteroid impact that coincided with the extinction of the dinosaurs. Over the years, researchers have gathered more and more evidence that the asteroid impact was indeed the trigger for the catastrophic extinction event.
The asteroid was huge—likely between 6 and 9 miles (9.7 and 14.5 kilometers) in diameter. But its sheer size is largely what caused it to disappear. The rock, which was about the size of Mount Everest, hurtled toward Earth at 15.5 miles per second (25 kilometers per second), According to NASA.
“Basically, all that kinetic energy is converted into heat,” Godris said. “When the thing hits the target, it’s going to explode even more; it’s going to vaporize.” The impact created a cloud of dust made up of the asteroid itself and the rock it landed on. The dust was scattered around the world, Block out sunlight and lower temperatures for years.leading to mass extinction.
As for the asteroid, Godris said: “All that remains of it is this chemical signature that has been deposited all over the world. It’s a little clay layer that you can recognize anywhere in the world, and it’s basically the same moment, 66 million years ago.”
Asteroids (and the smaller meteorites that break off from them) come in three main types, each with its own chemical and mineral composition: metallic, stony, and chondritic. In the new study, Goderis and his colleagues, including lead author Dr. Mario Fischer-Gudi of the University of Cologne in Germany, examined the chemical composition of the thin clay layer to uncover the asteroid’s secrets.
The researchers sampled 66-million-year-old rocks from Denmark, Italy and Spain and isolated fragments that contained the mineral ruthenium. (Like iridium, ruthenium is more abundant in space rocks than in Earth’s crust.) The team also analyzed ruthenium from other asteroid and meteorite impact sites. The scientists found that the chemical composition of ruthenium from 66 million years ago matches the chemical composition of ruthenium found in a certain type of chondritic meteorite.
“We saw a perfect overlap with the carbonaceous chondrite signatures,” Godris said. So the asteroid that killed the dinosaurs was likely a carbonaceous chondrite, an ancient space rock that often contains water, clay and organic (carbon-containing) compounds.
While carbonaceous chondrites make up the majority of rocks in space, only about 5 percent of meteorites that fall to Earth are of this type. “There is some diversity in carbonaceous chondrites, Some of them can smell.“But in hell, when the Chicxulub spacecraft landed,” Godris said, “you probably didn’t have time to breathe.”
Chicxulub-sized impacts only happen every 100 million to 500 million years. But since there’s only a small chance of Earth being hit by another asteroid or giant meteorite, Godris said it’s good to know “the physical and chemical properties of these objects, to think about how we can protect ourselves” from being hit by a large space rock.
Godris cited the DART 2022 mission, or Double Asteroid Redirection Test, in which NASA sent a spacecraft to deliberately deflect an asteroid. Knowing how different types of asteroids interact with the physical forces around them will be crucial to an effective planetary defense.
“Carbonaceous chondrites will react very differently than regular chondrites — they’re much more porous, they absorb more light, and they’ll absorb more impact if you point an object at them,” Godris said. “So we need to figure that out to get a similar response.”
Dr. Ed Young, a professor of cosmochemistry at the University of California, Los Angeles, who was not involved in the study, agreed with the findings.
The discovery “adds richness to our understanding of what happened” when the dinosaurs went extinct, he said. Young said the researchers’ assessment that the asteroid was a carbonaceous chondrite was “a solid conclusion.”
Kate Golembiewski He is a freelance science writer based in Chicago with interests in zoology, thermodynamics, and death.