IT'S 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 mass extinction of the dinosaur. ''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 almost complete disappearance of dinosaurs from the fossil record occurs roughly 66 million years ago, presumed to be the time they died out.
Using a new, more precise dating method, Professor Renne and his team dated rocks from a well known dinosaur extinction site in Montana to the more precise time of 66,043,000 years. The dating method relies on the decay rate of a radioactive potassium isotope.
The team then narrowed 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 show the impact was just 32,000 years before dinosaurs died out. Other studies suggested the Chicxulub impact was 300,000 years before the mass extinction.
Professor Renne says the dramatic change in the Earth's climate during the preceding million years, including long cold snaps, would have pushed many species to the brink.
Large volcanic eruptions also occurred around that time. ''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.