IT IS the world's coldest case. For decades, scientists have argued over what caused the almost overnight demise of land roaming dinosaurs 66 million years ago. Was it climate change, a violent volcanic eruption, a giant meteorite impact – or a combination of all three?
In the most significant advance towards solving the ultimate whodunnit, scientists have re-dated the impact of a more than 10-kilometre-wide meteor that slammed into Mexico to within the same time period as the dinosaur's mass extinction.
"We have shown that these events are synchronous to within a gnat's eyebrow, and therefore the impact clearly played a major role in extinctions," said the research leader, Paul Renne, from the University of California, Berkeley.
The disappearance of most dinosaurs from the fossil record occurs roughly 66 million years ago and is presumed to be the time they died out.
Using a new, more precise geochronological dating method, Professor Renne and his team dated rock samples from a well known dinosaur extinction site in Montana to the more precise time of 66,043,000 years, give or take 49,000 years.
The team then narrowed down the time of the Chicxulub impact by dating particles, known as tekties, which remain in the atmosphere for millennia after the initial collision.
The results showed the crash occurred 66,038,000 years ago, just 32,000 years before dinosaurs died out.
While 30,000 years seems like a long time between events, a German professor of palaeoceanography, Heiko Palike, said the ages suggested the impact coincided with the dinosaurs' downfall.
Professor Renne says the dramatic change in the Earth's climate during the preceding million years would have pushed many species to the brink of extinction.
"The impact was clearly the final straw that pushed Earth past the tipping point," said Professor Renne, whose findings are published in the journal Science.