Some discoveries change everything. Most just explain a lot. A few explain a LOT. The latter is the case of a new discovery in North Dakota – a killing field formed perhaps no more than hours after the event that caused the mass extinction of dinosaurs 66 million years ago … the asteroid or comet that smashed into the Earth near the Yucatan Peninsula and created the Chicxulub crater. Fossils found in what was once an inland sea show that the dinosaurs and other creatures there died in a rain of glass crystals formed when molten particles tossed skyward cooled and fell to the ground. And if that didn’t kill them, the seismic waves did. Is this the best picture ever of the day the Cretaceous Period ended? The day the K-T boundary was formed? The day the dinosaurs stood still?
“This is the first mass death assemblage of large organisms anyone has found associated with the K-T boundary. At no other K-T boundary section on Earth can you find such a collection consisting of a large number of species representing different ages of organisms and different stages of life, all of which died at the same time, on the same day.”
In an interview published in the University of California Berkeley News, Robert DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a doctoral student at the University of Kansas, explained how his very first career dig in the summer of 2013 triggered the interest that kept bringing him back to North Dakota to slowly reveal that the Hell Creek Formation — a fossil cornucopia of preserved remains of fish, tree trunks, conifer branches, dead mammals, mosasaurs, insects, Triceratops, dinoflagellates, ammonites and more — was created within 24 hours of the impact that created Chicxulub and ended Cretaceous. That day is described in “Prelude to Extinction: a seismically induced onshore surge deposit at the KPg boundary, North Dakota,” to be published in the journal Proceedings of the National Academy of Sciences.
“It’s like a museum of the end of the Cretaceous in a layer a meter-and-a-half thick.”
Mark Richards, a UC Berkeley professor emeritus and provost and professor of earth and space sciences at the University of Washington, and Walter Alvarez, the UC Berkeley Professor who is credited with coming up with the extinction-causing asteroid over 40 years ago, were brought in by DePalma to analyze this layer of history. (Photos and videos of the site and the researchers can be viewed here.) The key to linking it to the Chicxulub impact was perfectly-preserved beads of glass called tektites that blanketed the creatures to the point that they appeared in the gills of fossilized fish. These beads did more than fall – they were propelled from the sly at up to 200 miles-per-hour.
“You can imagine standing there being pelted by these glass spherules. They could have killed you.”
This is the most well-preserved example of death by tektites in the world and funnels of them in perfect shape were found buried in the ground. How did that happen? That was the second key discovery, according to DePalma.
“Tsunamis from the Chicxulub impact are certainly well-documented, but no one knew how far something like that would go into an inland sea. When Mark came aboard, he discovered a remarkable artifact — that the incoming seismic waves from the impact site would have arrived at just about the same time as the atmospheric travel time of the ejecta. That was our big breakthrough.”
Instead of a single tsunami, the area was hit with seismic waves called seiches that we now know were created far from the impact. Richards described the scene on that day 66 million years ago:
“The seismic waves start arising within nine to 10 minutes of the impact, so they had a chance to get the water sloshing before all the spherules (small spheres) had fallen out of the sky. These spherules coming in cratered the surface, making funnels — you can see the deformed layers in what used to be soft mud — and then rubble covered the spherules. No one has seen these funnels before.”
These layers of fossils, tektites and sediment are topped by a coating of iridium, a metal rarely found on Earth because it comes from … you guessed it … asteroids and comets. No matter where you dig around the world, when you hit the 66 million years ago mark, you find a layer of iridium that has come to be called the K-T or K-Pg boundary when Cretaceous ends and the Tertiary or Paleogene Period begins.
And now we know that the best place to see how the whole thing happened, including definitive proof that dinosaurs were still alive moments before the Chicxulub impact, is not in the Gulf of Mexico but in North Dakota.
The Peace Garden State is standing proud.