The age of the impact that created the Chicxulub Crater was pinned down using tiny blobs of rock that were ejected white-hot from the impact crater, cooled mid-air, and landed (in this case) in Haiti. The age for the extinction came from layers of (local) volcanic ash near the iridium-rich clay at a site in Montana. As confirmation, some of the ash was also dated using the decay of uranium to lead, as well.

The dates for the impact and extinction were essentially identical, within the error bars of about 30,000 years—or as Paul Renne, a UC-Berkeley professor who led the study, explained in a university press release, “We have shown that these events are synchronous to within a gnat’s eyebrow.”

The timeline the study sets out includes drastic climate changes in the million years before the meteor hit. As the Deccan Traps eruptions sputtered to life, their emissions drove several sharp drops in global temperature. After millions of years of a hot climate, these cooler periods were likely rough for many species. It was during this already difficult time that the meteor struck the killing blow.

A more detailed account of the Deccan Traps will be needed to establish this version of events, but this work represents significant progress towards fleshing out the demise of the dinosaurs.

The new dates also shorten up the time between the extinction and the return of vertebrate fossils (including mammals) in the Montana rocks. What had previously been thought to be a 400,000 year hiatus now appears to have been less than 50,000 years. Given that short timeframe, the creatures that show up in these fossils were probably survivors from other regions rather than new species that arose after the extinction cleared the ecological decks—preparing the way for the mammal revolution.

Science, 2013. DOI: 10.1126/science.1230492  (About DOIs).