Creatures among mega fossil haul died minutes after dinosaur-ending asteroid

1 Apr 20191.23k Views

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The destruction caused by the asteroid that killed off the dinosaurs has been shown in a new light, with scientists linking it to a recent mega haul of fossils.

Palaeontologists recently celebrated the discovery of a massive haul of fossilised remains of thousands of freshwater fish such as sturgeon and paddlefish, as well as burned tree trunks, dead mammals and even the partial carcass of a triceratops.

The fossil graveyard – now located in the US state of North Dakota – was once an inland sea, but the event that caused this mass destruction was located thousands of kilometres away.

Now, in a paper to be published next week to the Proceedings of the National Academy of Sciences, a team of US and European researchers has found strong evidence linking the event to the asteroid that hit off Mexico’s Yucatán Peninsula and wiped out the dinosaurs 66m years ago.

The site, dubbed Tanis, has been described by University of California Berkeley’s Mark Richards as “a museum of the end of the Cretaceous in a layer a metre-and-a-half thick”.

Evidence found at Tanis suggests that the fish did not wash over the land in a tsunami caused by the impact hours after the initial hit, but actually by seismic waves (called seiches) that arrived mere minutes afterwards. These waves would have been equivalent to a magnitude 10 or 11 earthquake, creating a standing wave in the inland sea reminiscent of water sloshing in a bathtub during an earthquake.

The proof of this occurring can be found by the discovery of melted rock beads (known as tektites) that 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.

“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,” Richards said. “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.”

The tektites would have come in on a ballistic trajectory from space, reaching terminal velocities of as high as 320kph. This raining fire was believed to be of such intensity that it ignited wildfires across the entire American continent, and possibly the world.

Dutch researcher Jan Smit was also able to find evidence that the many fish that died so soon after the impact had actually swallowed tektites, which were caught in their gills, showing them to be the first direct victims of the carnage.

“We have an amazing array of discoveries which will prove in the future to be even more valuable,” Smit said. “We have fantastic deposits that need to be studied from all different viewpoints. And I think we can unravel the sequence of incoming ejecta from the Chicxulub impact in great detail, which we would never have been able to do with all the other deposits around the Gulf of Mexico.”

Updated, 11.39am, 1 April 2019: This article was updated to clarify that the seiches would have been equivalent to a magnitude 10 or 11 earthquake, not 100.

Colm Gorey is a journalist with Siliconrepublic.com

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