Sealing the fate of the dinosaurs
It's official: It really was an asteroid, and not massive volcanic activity, that wiped out the dinosaurs (and more than half the other species on earth) at the Cretaceous-Tertiary boundary some 65 million years ago.
That's the conclusion of a painstaking review of all the available evidence by a panel of 41 international experts and published today in the journal Science.
But you knew that already, right? So what's all the fuss about? And, more importantly, why do we need a panel of experts to spend so much time and money exhaustively reviewing the evidence and producing a ruling on an issue that has long since been laid to rest?
Well (with apologies to Donald Rumsfeld), the fact is that we suspected we knew, but we didn't know that we knew for sure.
The problem is that the asteroid extinction theory is such a powerful explanation, such a catchy story, that it passed into the common narrative of the dinosaurs' demise long before the evidence to substantiate it had been consolidated.
But the asteroid theory is not the only explanation for the Cretaceous-Tertiary mass extinction.
Behind the scenes a dedicated band of geologists, geochemists and palaeontologists have argued that a series of massive volcanic eruptions across the Deccan Traps in India could well have been the real culprit.
These eruptions, spread over more than a million years, spewed billions of tonnes of lava - enough to fill the Black Sea twice over - across the earth's surface, blackening the sky with clouds of ash and triggering acid rain on a global scale.
It all comes down to a question of timing, and of interpretation of the geological record.
The supporters of the Deccan Traps theory argue that the asteroid impact at Chicxulub in Mexico, actually occurred some 300 000 years before the KT extinction boundary.
If that's true then the devastation it caused can only have been a contributory factor in the demise of the dinosaurs - just one of many smoking guns.
But the review team, lead by Peter Schulte at the University of Erlangen-Nurnberg in Germany, has discounted the idea that there was a significant gap between the Chicxulub impact and the rapid disappearance of fossils from the geological record, which they claim is based on a misinterpretation of the rock strata around the impact site.
The strongest evidence for the impact extinction theory has always been the layer of iridium deposits in geological samples dating from the KT boundary.
Iridium is very rare in the earth's crust, but a common component in asteroids. The latest research shows the decline in fossil abundance and species variety correlates very closely with the iridium layer, indicating that the extinction event followed immediately after the asteroid impact.
According to Dr Joanna Morgan from the Department of Earth Sciences at Imperial College London and a co-author on the review.
"We now have great confidence that an asteroid was the cause of the KT extinction," she says.
The impact would have triggered large-scale wildfires, massive earthquakes, and continental landslides which in turn created huge tsunamis, she argues, but the final nail in the dinosaurs coffin would have been the huge volume of material blasted into the atmosphere at high velocity.
"This shrouded the planet in darkness and caused a global winter, killing off many species that couldn't adapt to this hellish environment".
It does seem to be the end for one of science's great known unknowns.