Hat-tip to Gordo: it appears that the Chicxulub impact event did not kill the dinosaurs. Rather, it was another impact, which took place hundreds of thousands of years later, combined with a general increase in volcanism and volatile climate change. Since it’s easier to date geological strata to that level of precision by the animals they contain than by radiometric dating, the best evidence comes from the impact crater itself.
Marine sediments drilled from the Chicxulub crater itself, as well as from a site in Texas along the Brazos River, and from outcrops in northeastern Mexico reveal that Chicxulub hit Earth 300,000 years before the mass extinction. Small marine animal microfossils were left virtually unscathed, says Keller.
“In all these localities we can analyze the marine microfossils in the sediments directly above and below the Chicxulub impact layer and cannot find any significant biotic effect,” said Keller. “We cannot attribute any specific extinctions to this impact.” No one has ever published this critical survival story before, she said. Keller’s research was funded by the National Science Foundation.
I expect creationists to howl that this just means that scientists don’t know what they’re talking about.
My only response to this is that it brings the K-T extinction event in line with the other four Phanerozoic mass extinctions, which appear to have multiple, interrelated causes. Fortunately, since the K-T event was only 65 million years ago, it’s possible to find another impact crater; earlier events are so far back in time that continental drift has erased any possible impact crater.
Even with this revision, scientists appear to know more about what killed the dinosaurs than about what killed 95% of all marine genera at the end of the Permian. I suppose it just goes to show how difficult it is to retrodict what happened hundreds of millions of years ago based on what’s been preserved.