(CNN) – Sixty-six million years ago, the history of life on Earth took a dramatic turn when an asteroid collided with what is now the Yucatán Peninsula in Chicxulub, Mexico. The aftermath of the collision led to the extinction of about 75% of animal species, including most dinosaurs except birds. But virtually nothing remains of the asteroid itself.
In a new study published on Thursday in the academic journal ScienceResearchers have reconstructed the chemical identity of the asteroid that triggered the planet's fifth mass extinction event. The dinosaur killer was a rare clay-rich mudball containing materials from the dawn of the solar system, the findings suggest.
Although the Chicxulub asteroid landed tens of millions of years ago, learning about this ancient space rock is important because “it is part of a broader view of understanding the dynamic nature of our solar system,” said study co-author Dr. Steven Goderis, a research professor of chemistry at the Université Libre de Bruxelles.
Scientists hypothesized in 1980 that a collision with a giant space rock caused the death of the dinosaurs. At the time, researchers did not find the asteroid itself, but a thin layer of the metal iridium in rocks around the world dating back 66 million years. Iridium is rare in the Earth's crust but abundant in some asteroids and meteorites.
Some members of the broader scientific community were skeptical of the hypothesis. However, in 1991, scientists discovered that the Chicxulub crater was just the right age to have been formed by the impact of a massive asteroid coinciding with the demise of the dinosaurs. Over the years, researchers have gathered more and more evidence that the asteroid impact was indeed the impetus for the cataclysmic extinction.
The asteroid was huge, probably between 9.7 and 14.5 kilometers in diameter. But its colossal size is the cause of its grand demise. The rock, roughly the size of Mount Everest, hurtled toward Earth, traveling at 25 kilometers per second, According to NASA.
“Basically, all this kinetic energy is converted to heat,” Goderis explained. “When it hits the target, it vaporizes rather than explodes.” The impact created a cloud of dust composed of the asteroid itself and the rock it landed on. The dust spread across the globe, blotting out sunlight and causing a temperature drop for yearswhich caused a mass extinction.
As for the asteroid, “there’s nothing left except this chemical signature that’s deposited all over the globe,” Goderis said. “This forms this tiny layer of clay that you can recognize everywhere in the world, and it’s basically the same instant in time, 66 million years ago.”
Asteroids (and the smaller meteoroids that break off from them) come in three main varieties, each with its own chemical and mineral composition: metallic, stony, and chondritic. In the new study, Goderis and his colleagues, including the study's lead author Dr. Mario Fischer-Gödde of the University of Cologne in Germany, examined the chemical composition of the thin clay layer to unlock the asteroid's secrets.
The researchers took samples of 66-million-year-old rocks from Denmark, Italy and Spain and isolated the parts that contained the metal 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 the 66 million-year-old ruthenium matched that of ruthenium found in a certain type of chondritic meteorite.
“We realized that there is a perfect overlap with the signatures of carbonaceous chondrites,” Goderis said. Therefore, 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.
Although carbonaceous chondrites make up the majority of rocks in space, only about 5% of meteorites that fall to Earth fall into this category. “There is quite a bit of diversity in carbonaceous chondrites, and some of them can smell“They probably wouldn’t have had time to get a good sniff,” Goderis said. But in hell, when the Chicxulub impactor hit, Goderis said, “they probably wouldn’t have had time to get a good sniff.”
Impacts of the magnitude of Chicxulub only occur every 100 million to 500 million years. But because there is still a remote chance that Earth could cross paths with another giant asteroid or meteorite, Goderis said it is good to know “the physical and chemical properties of these objects, in order to think about how to protect ourselves” from a collision with a large space rock.
Goderis cited the 2022 DART mission, or Double Asteroid Redirection Test, in which NASA sent a spacecraft to intentionally divert an asteroid from its path. Knowing how different types of asteroids interact with the physical forces around them would be critical to an effective planetary defense operation.
“The carbonaceous chondrite will react completely differently than an ordinary chondrite: it is much more porous, it is much lighter and it will absorb much more of an impact if an object is sent towards it. So we need to learn about this in order to have a corresponding response,” Goderis said.
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.
He said the discovery “adds richness to our understanding of what happened” when the dinosaurs became extinct. Young said the researchers’ assessment that the asteroid was a carbonaceous chondrite “is a solid conclusion.”
– Kate Golembiewski is a Chicago-based freelance science writer with a passion for zoology, thermodynamics, and death.
