New evidence that asteroid caused dinosaur demise

In an attempt to discover what wiped out the dinosaurs, researchers have now determined the most precise dates yet for dinosaur extinction and for the well-known impact that occurred around the same time. The researchers say the dates are so close that they provide new evidence that a comet or asteroid – first linked to dinosaur extinction in 1980 – was responsible for the dinosaurs’ demise.

“The impact was clearly the final straw that pushed Earth past the tipping point,” said Professor Paul Renne, director of the Berkeley Geochronology Centre (BGC) and lead author of the paper published in Science. “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.”

Renne and colleagues decided to re-date the dinosaur extinction, which happened at the boundary between the Cretaceous and Tertiary periods (the KT boundary) after recalibrating the 20-year-old accepted date and finding it to be 180,000 years before the impact.

"Everybody had always looked at the age for the KT boundary and compared it with the ages that we had gotten for the tektites and the melt rock from the Chicxulub crater and said, 'Ooh yeah, this is pretty much the same age,'" Renne said. "But they are not. They differ by 180,000 years, actually. So, from simply this esoteric calibration issue, I started to realise, 'Wow, there is a real problem here.'"

The researchers then attempted to get some more data by dating tektites – debris ejected during extraterrestrial impacts – from Haiti and analysed them using the recalibrated argon-argon radiodating technique. The results agreed with recalibrated previous data, but were much more precise.

Renne makes it clear that despite the synchronous extinction and impact it doesn’t mean that the impact was the only cause. There was dramatic climate variation over the previous million years which probably brought many of the organisms to the brink of extinction; the impact was just the final straw.

“These precursory phenomena made the global ecosystem much more sensitive to even relatively small triggers, so that what otherwise might have been a fairly minor effect shifted the ecosystem into a new state. The impact was the coupe de grace,” concluded Renne.

Reference: "Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary," by P.R. Renne et al., Science, 2013.