When an asteroid hit the Gulf of Mexico 66 million years ago, Earth changed forever. The impact caused a mass extinction event, killing around 60 per cent of the planet’s species – including all of the non-avian dinosaurs.
Now, new evidence suggests that the asteroid behind the destruction did not come from nearby, but from very far away: beyond the outer parts of the Solar System, in fact. The authors of the research, published in the journal Science, say that this evidence finally settles long-standing debates about this crucial part of the planet’s history.
“This is one of those studies that makes you stop in your tracks and think about the cosmic interconnectedness of everything,” palaeontologist Prof Stephen Brusatte, who was not involved, explained to BBC Science Focus.
“It's remarkable that one day, 66 million years ago, dinosaurs across the world were going about their business as they had been for tens of millions of years, and then suddenly this asteroid arrives out of nowhere and changes the world forever. But it didn't arrive out of nowhere, it had an origin, and that origin was out in the far reaches of our Solar System, beyond Jupiter.”
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This moment in time, between the Cretaceous and Paleogene eras, is captured in the chemistry of the layers of rock buried under the Earth’s surface, all over the world. In geology, this layer of rock is known as the K-Pg boundary. Here, scientists have previously found high levels of platinum-group elements (including iridium, ruthenium, osmium, rhodium, platinum, and palladium).
These elements are rare on Earth but common in meteorites. Nevertheless, some scientists have previously thought that the high levels of these elements could have been caused by widespread volcanic activity. Others thought, however, that the specific composition of elements, known as the isotopic signature, aligned more with that of asteroids.
To settle the debate, the researchers took samples from the K-Pg boundary. Comparing against samples from other asteroid impacts, the team discovered that the levels of ruthenium (Ru) isotopes were not similar to those from Earth or other meteorite types. Instead, they closely matched extraterrestrial carbonaceous chondrites: a type of asteroid that forms in the outer Solar System.
“To think that this bit of space junk, from such a far-off and remote place, somehow, against the odds, intersected with the Earth and the dinosaurs. It's such an unlikely story, but it actually happened,” said Brusatte.
About our expert
Steve Brusatte is a professor of palaeontology at the University of Edinburgh who specialises in the anatomy, genealogy, and evolution of dinosaurs. He served as the dinosaur consultant in the film Jurassic World: Dominion, as well as BBC's Walking with Dinosaurs. His research has been published in journals including Nature, Ecology and Evolution, and Current Biology.
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