A major international study has found overwhelming evidence that a massive asteroid impact in did indeed wipe out the dinosaurs 65 million years ago.
The theory has long been controversial. Many scientists have suggested that the Cretaceous-Paleogene (K-Pg) extinction actually occurred 300,000 years after the Chicxulub impact, and was caused by something else - possibly a second asteroid strike, or volcanic activity at the Deccan Traps in what is now India.
Now, an interdisciplinary team of 41 scientists from 12 nations has concluded that the asteroid impact did indeed cause the extinction, triggering earthquakes, tsunamis 1,000 feet high, raging fires and darkness across the globe.
As many as 70 percent of all species on earth were wiped out.
The evidence for the impact comes in the form of iridium, found in a clay layer all around the world that dates from the time of impact. While it's extremely rare in the earth's crust, it's common in asteroids.
"This clay layer - with evidence for it being impact in origin - is found at every well-preserved K-Pg boundary site in the world, showing a truly global event," says University of Texas geophysicist Sean Gulick.
In some sites close to the impact, there are two layers, and some of the recent controversy stems from this. But the team points out that at more distant sites there's only a single layer.
And the Deccan Traps hypothesis doesn't stand up either, say the scientists.
Because deep ocean temperatures were largely unaffected, the the climate recovered relatively rapidly, they say. If volcanic activity were to blame, the changes would have been far slower.
"The Chicxulub impact was an extremely rapid perturbation of the Earth's ecosystems, at a scale greater than that of any single volcanic event at the time, or of any other impact known since life became prevalent on Earth," added Gulick. "The rate of change and scale of the effects were clearly the cause of the mass extinction at the end of the Cretaceous."
The research is published in Science.