THE DAY THE DINOSAURS DIED

New BBC documentary, Dinosaurs: The Final Day, presented by Sir David Attenborough, digs into a fossil site that may have recorded the moment an asteroid wiped out almost all life on Earth. Holly Spanner met with Robert DePalma, one of the palaeontologists at the site, to find out more about the significance of this discovery...

- Holly Spanner

YOU’VE BEEN WORKING AT TANIS, A TOP-SECRET FOSSIL LOCATION IN NORTH DAKOTA. WHEN WAS THIS SITE LAID DOWN?

We worked out the site was deposited during the fallout of coarse ejecta material [debris] from an asteroid impact. To give it probably the broadest span possible, we can say the site is constrained [dated] to the first one to two hours [after asteroid impact], maximum, because that’s how long ejecta would have been falling for.

HAVE YOU FOUND ANY OTHER EVIDENCE THAT THIS SITE WAS CREATED RIGHT AFTER THE ASTEROID IMPACT?

We have constrained the site in multiple different ways, using plants, pollen, marine dinoflagellates and different organisms. In addition to that, we have physics. When the asteroid hit, material was thrown out of the crater [as vaporised and molten rock] and out of the atmosphere, where it cooled and solidified, then fell back to Earth in a rain of glowing glass droplets, or spherules. These spherules would have started to arrive at Tanis tens of minutes after impact, raining down for around an hour, two at most. The impact glass has been radiometrically dated, and it dates to the very end of the Cretaceous. Basically, it correlates exactly with the Chicxulub impact event [the moment the asteroid that wiped out the dinosaurs hit Earth in Mexico].

WHAT IS THE SIGNIFICANCE OF THE SPHERULES?

You’re dealing with stuff that was molten by the impact, and they therefore contain contamination from the impactor itself.