66-Million-Year-Old Deathbed Linked to Dinosaur-Killing Meteor

A meteor impact 66 million years ago generated a tsunami-like wave in an inland sea that killed and buried fish, mammals, insects, and a dinosaur, the first victims of Earth’s last mass extinction event. The death scene from within an hour of the impact has been excavated at an unprecedented fossil site in North Dakota. (Image: Courtesy of Robert DePalma)
A meteor impact 66 million years ago generated a tsunami-like wave in an inland sea that killed and buried fish, mammals, insects, and a dinosaur, the first victims of Earth’s last mass extinction event. The death scene from within an hour of the impact has been excavated at an unprecedented fossil site in North Dakota. (Image: Courtesy of Robert DePalma)

The beginning of the end started with violent shaking that raised giant waves in the waters of an inland sea in what is now North Dakota. Then, tiny glass beads began to fall like birdshot from the heavens. The rain of glass was so heavy it may have set fire to much of the vegetation on land. In the water, fish struggled to breathe as the beads clogged their gills.

The heaving sea turned into a 30-foot wall of water when it reached the mouth of a river, tossing hundreds, if not thousands, of freshwater fish — sturgeon and paddlefish — onto a sand bar and temporarily reversing the flow of the river. Stranded by the receding water, the fish were pelted by glass beads up to 5 millimeters in diameter, some burying themselves inches deep in the mud.

Fossilized fish piled one atop another, suggesting that they were flung ashore and died stranded together on a sand bar after the seiche withdrew. (Image: Courtesy of Robert DePalma)

Fossilized fish piled one atop another, suggesting that they were flung ashore and died stranded together on a sand bar after the seiche withdrew. (Image: Courtesy of Robert DePalma)

The torrent of rocks, fine sand, and small glass beads continued for another 10 to 20 minutes before a second large wave inundated the shore and covered the fish with gravel, sand, and fine sediment, sealing them from the world for 66 million years.

This unique, fossilized graveyard — fish stacked one atop another and mixed in with burned tree trunks, conifer branches, dead mammals, mosasaur bones, insects, the partial carcass of a Triceratops, marine microorganisms called dinoflagellates, and snail-like marine cephalopods called ammonites — was unearthed by paleontologist Robert DePalma over the past six years in the Hell Creek Formation, not far from Bowman, North Dakota.

The evidence confirms a suspicion that nagged at DePalma in his first digging season during the summer of 2013 — that this was a killing field laid down soon after the asteroid impact that eventually led to the extinction of all ground-dwelling dinosaurs. The impact at the end of the Cretaceous Period, the so-called K-T boundary, exterminated 75 percent of life on Earth.

DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a doctoral student at the University of Kansas, said:

In a paper published in the journal Proceedings of the National Academy of Sciences, he and his American and European colleagues, including two University of California, Berkeley, geologists, describe the site, dubbed Tanis, and the evidence connecting it with the asteroid or comet strike off Mexico’s Yucatan Peninsula 66 million years ago.

That impact created a huge crater, called Chicxulub, in the ocean floor and sent vaporized rock and cubic miles of asteroid dust into the atmosphere. The cloud eventually enveloped Earth, setting the stage for Earth’s last mass extinction. Mark Richards, a UC Berkeley professor emeritus of Earth and planetary science who is now provost and professor of Earth and space sciences at the University of Washington, said:

Richards and Walter Alvarez, a UC Berkeley Professor of the Graduate School who 40 years ago first hypothesized that a comet or asteroid impact caused the mass extinction, were called in by DePalma and Dutch scientist Jan Smit to consult on the rain of glass beads and the tsunami-like waves that buried and preserved the fish. The beads, called tektites, formed in the atmosphere from rock melted by the impact.

Tsunami vs seiche

Richards and Alvarez determined that the fish could not have been stranded and then buried by a typical tsunami, a single wave that would have reached this previously unknown arm of the Western Interior Seaway no less than 10 to 12 hours after the impact 3,000 kilometers away, if it didn’t peter out before then. Their reasoning: The tektites would have rained down within 45 minutes to an hour of the impact, unable to create mudholes if the seabed had not already been exposed.

Walter Alvarez and Robert DePalma at the Tanis outcrop in North Dakota. (Image: Courtesy of Robert DePalma)

Walter Alvarez and Robert DePalma at the Tanis outcrop in North Dakota. (Image: Courtesy of Robert DePalma)

Instead, they argue, seismic waves likely arrived within 10 minutes of the impact from what would have been the equivalent of a magnitude 10 or 11 earthquake, creating a seiche (pronounced saysh), a standing wave, in the inland sea that is similar to water sloshing in a bathtub during an earthquake.

Though large earthquakes often generate seiches in enclosed bodies of water, they’re seldom noticed, Richards said. The 2011 Tohoku quake in Japan, a magnitude 9.0, created six-foot-high seiches 30 minutes later in a Norwegian fjord 8,000 kilometers away. Richards added:

The tektites would have come in on a ballistic trajectory from space, reaching terminal velocities of between 100 and 200 miles per hour, according to Alvarez, who estimated their travel time decades ago. Richards said:

Many believe that the rain of debris was so intense that the energy ignited wildfires over the entire American continent, if not around the world. DePalma said:

At least two huge seiches inundated the land, perhaps 20 minutes apart, leaving six feet of deposits covering the fossils. Overlaying this is a layer of clay rich in iridium, a metal rare on Earth, but common in asteroids and comets. This layer is known as the K-T, or K-Pg boundary, marking the end of the Cretaceous Period and the beginning of the Tertiary Period, or Paleogene.

Iridium

In 1979, Alvarez and his father, Nobelist Luis Alvarez of UC Berkeley, were the first to recognize the significance of iridium that is found in 66 million-year-old rock layers around the world. They proposed that a comet or asteroid impact was responsible for both the iridium at the K-T boundary and the mass extinction.

Tektites, 1 millimeter spheres of glass, recovered from the Tanis fossil bed. (Image: Courtesy of Robert DePalma)

Tektites, 1-millimeter spheres of glass, recovered from the Tanis fossil bed. (Image: Courtesy of Robert DePalma)

The impact would have melted the bedrock under the seafloor and pulverized the asteroid, sending dust and melted rock into the stratosphere, where winds would have carried them around the planet and blotted out the sun for months, if not years. Debris would have rained down from the sky — not only tektites, but also rock debris from the continental crust, including shocked quartz, whose crystal structure was deformed by the impact.

The iridium-rich dust from the pulverized meteor would have been the last to fall out of the atmosphere after the impact, capping off the Cretaceous. Alvarez said:

Key confirmation of the meteor hypothesis was the discovery of a buried impact crater, Chicxulub, in the Caribbean and off the coast of the Yucatan in Mexico, that was dated to exactly the age of the extinction. Shocked quartz and glass spherules were also found in K-Pg layers worldwide.

Jan Smit, Mark Richards and Walter Alvarez at the North Dakota site of dinosaur-killing meteor’s first victims. (Image: Courtesy of Robert DePalma)

Jan Smit, Mark Richards, and Walter Alvarez at the North Dakota site of dinosaur-killing meteor’s first victims. (Image: Courtesy of Robert DePalma)

The new discovery at Tanis is the first time the debris produced in the impact was found along with animals killed in the immediate aftermath of the impact. Alvarez said:

Tektites

Jan Smit, a retired professor of sedimentary geology from Vrije Universiteit in Amsterdam in The Netherlands who is considered the world expert on tektites from the impact, joined DePalma to analyze and date the tektites from the Tanis site. Many were found in near perfect condition embedded in amber, which at the time was pliable pine pitch.

Smit said:

Fish carcasses and two logs tossed together by the seiche created by seismic waves from the meteor impact. (Image: Courtesy of Robert DePalma)

Fish carcasses and two logs tossed together by the seiche created by seismic waves from the meteor impact. (Image: Courtesy of Robert DePalma)

The tektites in the fishes’ gills are also a first. Smit added:

Smit also noted that the buried body of a Triceratops and a duck-billed hadrosaur proves beyond a doubt that dinosaurs were still alive at the time of the impact, saying:

A perfectly preserved fish tail from Tanis deposit. (Image: Courtesy of Robert DePalma)

A perfectly preserved fish tail from Tanis deposit. (Image: Courtesy of Robert DePalma)

Smit said:

Provided by: University of California – Berkeley [Note: Materials may be edited for content and length.]

Like this article? Subscribe to our weekly email for more!     

Cold-blooded Juvenile Killers Are Everywhere in China
Playwright on China’s Shocking School Bullying Culture