The Day the Dinosaurs Died

I continue to be impressed by Douglas Preston's science writing. He's probably best known as a novelist, both on his own and in collaboration with Lee Child. But a couple of years ago, he published The Lost City of the Monkey God, about the discovery of Mayan ruins lost for centuries in the Honduran jungle and his struggle with leptospirosis, which he contracted while writing the book. It was one of the best non-fiction books I've read in years.

Now he's written The Day the Dinosaurs Died, a long article in the New Yorker, about what may be the most significant paleontological find of all time—fossils that were buried minutes after the impact that killed the dinosaurs. The article is also a profile of the young geologist, Robert DePalma, who discovered them.

The following day, DePalma noticed a small disturbance preserved in the sediment. About three inches in diameter, it appeared to be a crater formed by an object that had fallen from the sky and plunked down in mud. Similar formations, caused by hailstones hitting a muddy surface, had been found before in the fossil record. As DePalma shaved back the layers to make a cross-­section of the crater, he found the thing itself—not a hailstone but a small white sphere—at the bottom of the crater. It was a tektite, about three millimetres in diameter—the fallout from an ancient asteroid impact. As he continued excavating, he found another crater with a tektite at the bottom, and another, and another. Glass turns to clay over millions of years, and these tektites were now clay, but some still had glassy cores. The microtektites he had found earlier might have been carried there by water, but these had been trapped where they fell—on what, DePalma believed, must have been the very day of the disaster.

“When I saw that, I knew this wasn’t just any flood deposit,” DePalma said. “We weren’t just near the KT boundary—this whole site is the KT boundary!” From surveying and mapping the layers, DePalma hypothesized that a massive inland surge of water flooded a river valley and filled the low-lying area where we now stood, perhaps as a result of the KT-impact tsunami, which had roared across the proto-Gulf and up the Western Interior Seaway. As the water slowed and became slack, it deposited everything that had been caught up in its travels—the heaviest material first, up to whatever was floating on the surface. All of it was quickly entombed and preserved in the muck: dying and dead creatures, both marine and freshwater; plants, seeds, tree trunks, roots, cones, pine needles, flowers, and pollen; shells, bones, teeth, and eggs; tektites, shocked minerals, tiny diamonds, iridium-laden dust, ash, charcoal, and amber-smeared wood. As the sediments settled, blobs of glass rained into the mud, the largest first, then finer and finer bits, until grains sifted down like snow.

 If you have any interest at all in dinosaurs, paleontology, or geography, you will enjoy this article. It's a marvellous example of science journalism that reminds me of the great John McPhee at his best.

DePalma's research has recently been published in the Proceedings of the National Academy of Sciences.

The Chicxulub impact played a crucial role in the Cretaceous–Paleogene extinction. However the earliest postimpact effects, critical to fully decode the profound influence on Earth’s biota, are poorly understood due to a lack of high-temporal-resolution contemporaneous deposits. The Tanis site, which preserves a rapidly deposited, ejecta-bearing bed in the Hell Creek Formation, helps to resolve that long-standing deficit. Emplaced immediately (minutes to hours) after impact, Tanis provides a postimpact “snapshot,” including ejecta accretion and faunal mass death, advancing our understanding of the immediate effects of the Chicxulub impact. Moreover, we demonstrate that the depositional event, calculated to have coincided with the arrival of seismic waves from Chicxulub, likely resulted from a seismically coupled local seiche.

You'll probably want to read the paper as after you've read Preston's article. It's cleanly written and despite lots of technical details, should be comprehensible to lay readers.

Update: Here's a short video about the discovery from the PBS show, Nova.