New evidence released Thursday has strengthened the argument that the dinosaurs (and many other animal species) went extinct as a result of an asteroid impact 66 million years ago.
The Chicxulub Crater, located in Mexico's Yucatan Peninsula, was impacted by an asteroid approximately 66,038,000 years ago, an event that was "synchronous to within a gnat's eyebrow" of when the dinosaurs went extinct, says the study's lead author Paul Renne, director of the University of California, Berkeley's Geochronology Center.
"Previously, the dating wasn't good enough, there was enough wiggle room for people to say the dates don't agree, so maybe something else killed the dinosaurs," he says. "Overall, this will strengthen the argument that the extinctions were clearly related to the impact."
The new dating, which pushes back the asteroid impact by more than 180,000 years, is accurate to within 11,000 years.
Renne says that dinosaur populations likely began declining more than a million years before their extinction due to global climate change and some other poorly understood global changes. But that the asteroid and its aftermath likely dealt the final blow.
"I think we have enough evidence to suggest that the asteroid was the straw that broke the camel's back," he says. "But I think we'd be doing ourselves a disservice if now we assumed we knew the whole story."
What's still not known is the mechanism by which the dinosaurs died. It's unlikely that they all died at once—scientists have hypothesized that atmospheric dust kicked up by the impact may have blocked out the sun for an extended period of time, or gases released by the impact may have rapidly changed earth's climate.
"Our study does not clarify the mechanisms by which they died except it had to have happened on a timescale of less than 32,000 years," he says. "That's a pretty narrow window for something to happen 66 million years ago, but it's plenty of time for atmospheric dust and gases to have played a role."