A layer of asteroid material in the Chicxulub impact crater matches material deposited around the world at the same time, confirming the connection between the two. This discovery also helps us measure how long lifeforms had to survive before the world returned to something approaching normality after the catastrophic event.
When a distinctive layer of rocks enriched in iridium and other heavy elements was found in many parts of the planet, it was a truly world-changing discovery. More than anything else, it took the idea that an asteroid or comet caused the death of the non-avian dinosaurs from fringe theory to dominant explanation. Iridium is much more common in small space objects than in the Earth's crust, because so much of it sunk into the Earth's core.
The timing of the layer's formation matched the dinosaurs' demise, inspiring a search for a suitably-timed crater. When the Chicxulub crater was found, many considered the case closed. However, some doubters remained. Most accepted there had indeed been a catastrophic collision with a space rock, but argued other factors played a larger role in the mass extinction. A few, however, questioned whether we could even be sure the crater and the iridium layer had anything to do with each other.
Professor Sean Gulick of the University of Texas, Austin, thinks that part of the debate is over. In the course of drilling into the central peak of the Chicxulub crater, Gullick and other scientists from IODP-ICDP Expedition 364 found a store of iridium thicker than at other sites from the same era. The extraterrestrial nature of the find is confirmed in Science Advances through the presence of other elements much more common in asteroids than the Earth's crust.
"It puts to bed any doubts that the iridium anomaly [in the geologic layer] is not related to the Chicxulub crater," Gulick said in a statement.
There's also plenty in the research for those who already thought the connection between the crater and the high-iridium layer was settled. In most places, the post-impact layer is so thin it's hard to measure how long it took to deposit. However, at the source, it is up to five centimeters (two inches) thick, allowing Gulick and co-authors to establish that it fell over something like 20 years.
"If you're actually going to put a clock on extinction 66 million years ago, you could easily make an argument that it all happened within a couple of decades, which is basically how long it takes for everything to starve to death," Gulick said.
The thickness of the deposit also allows us to examine its rarer constituents to a level of detail not possible elsewhere. This might help settle the question of whether what hit us was an asteroid, as the paper calls the spacerock throughout, or a comet as recently suggested.