It's been more than 30 years since UC Berkeley researchers first suggested that the extinction of the dinosaurs was probably linked to a massive comet or asteroid impact, known as Chicxulub, off the Yucatan coast. The idea was that the collision from space, which left a 110-mile-wide crater off the coast of Mexico, would have cast off debris that wrapped all the way around Earth, altering the climate and resulting in the global extinction.
But that story hasn't passed muster everywhere. Because different methods of estimating when the extinction and the impact occurred have yielded different answers -- some studies concluded that the asteroid hit as much as 300,000 years before dinosaurs went extinct -- some people have argued that other circumstances, including volcanic eruptions or climate change, must have had more to do with the dinosaurs' end than a whopper of an asteroid.
Now, using highly refined methods of determining the ages of rocks, another team from Berkeley has demonstrated that the extinction and the impact occurred at almost exactly the same time: just over 66 million years ago. They reported their findings (abstract free, subscription required for full text) Thursday in the journal Science.
"The impact was clearly the final straw that pushed the Earth past the tipping point," said study lead author and UC Berkeley earth scientist Paul Renne, in a statement. "We have shown that these events are synchronous to within a gnat's eyebrow."