At first there was a big shock. Then a 30-meter-high water wave boomed, which threw fish in today's North Dakota on a sandbar. Then there was a hail of molten rock, falling fish and soon dying land creatures. Then the fires started.
For decades scientists have been presuming that the downfall came about when a huge asteroid or comet hit the earth just off the Mexican peninsula of Yucatan. The new study describes a scenario of how this cosmic influence has killed species thousands of miles away and completed the so-called Cretaceous.
An ancient rock stratum found in a place known as "Tanis" in North Dakota's Hell. Creek Formation revealed the fossilized remains of fish, snail-like marine creatures known as ammonites, and a marine reptile known as Mosasaur, as well as land animals including mammals and triceratops. Mixed with the fossils were fragments of burned tree trunks, sediments and tiny glass beads known as tektites.
The research team behind the find was led by Robert DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a Ph.D. student at the University of Kansas. DePalma has been working on the Tanis site since 2013, and says it sheds new light on the chain of events that gave rise to the famous geological and biological dividing line known as the Cretaceous-Paleogene border, the Chalk-Tertiary border or simply known as K-Pg or KT-limit.
"This is the first mass murder of large organisms somebody has associated with the KT boundary," DePalma said in a press release. "At no other KT borderline on earth is there such a collection that consists of a large number of species representing the age of organisms and different stages of life, all dying at the same time on the same day."  Three researchers "class =" JsEnabled_Op (0) JsEnabled_Bg (n) Trsdu (.42s) Bgr (nr) Bgz (cv) StretchedBox W (100%) H (100%) ie-7_H (a) "itemprop = "url" style = "background-image: url (https://s.yimg.com/ny/api/res/1.2/uz9TfsJYua7eSgHaIQMP1w–~A/YXBwaWQ9aGlnaGxhbmRlcjtzbT0xO3c9NjMwO2g9NDIw/http://media.zenfs.com/en- US / homerun / geekwire_312 / 991e1f26313932ac032ecb245c5b4a21); "src =" https://s.yimg.com/g/images/spaceball.gif "data-reactid =" 41 "/>
The researchers Jan Smit, Mark Richards, and Walter Alvarez are gathered together at the Tanis site. (Robert DePalma photo via UC-Berkeley)
DePalma and his colleagues reconstructed the sequence of events on that fatal day by delineating the rock section
"It is like a museum at the end of the chalk in a layer of one and a half meters thick," said Mark Richards, co-author of the study, and was a professor of Earth and Space Sciences at the University of Washington n.
The detective work was based on an analysis by Richards and Walter Alvarez, a professor at the University of California at Berkeley, who helped create the original asteroid hypothesis almost 40 years ago. They evaluated the evidence of the tsunami-like wave and the hail of glass beads and set out a scenario that began with the asteroid impact that triggered a magnitude 10 or 11 earthquake.
This seismic shock could have a number of implications Standing Waves, also known as Seiche, in a body of water known as the Western Interior Seaway, which, according to scientists, was pulled through the middle of North America in the Cretaceous.
Meanwhile, the asteroid impact had created a massive cloud of molten rock that turned into spherical tectites and rained out of space over a wide area of the earth's surface. Richards and Alvarez concluded that the standing waves must have flushed fish before the deadly hail from the deadly hail.
"The seismic waves begin within nine to ten minutes of the impact, giving them a chance to float the water before all the bullets fall from the sky," Richards explains , "These globules entered the surface and made funnels – you can see the deformed layers in early soft mud – and then debris covered the beads."
The sediment layer that covered the debris was rich in iridium, confirming the link to Alvarez's giant asteroid hypothesis.
"When we proposed the impact hypothesis to explain the great extinction, it was based only on finding an anomalous concentration of iridium – the fingerprint of an asteroid or comet," said Alvarez. "Since then, the evidence has gradually built up. But it never occurred to me that we would find such a death bed. "
The researchers say the carnage must have started swiftly – too fast to explain it by a tsunami emanating from the site of Chicxulub's asteroid impact. "A tsunami would have taken at least 17 or more hours to reach the site from the crater, but seismic waves – and a subsequent ascent – would have reached it in ten minutes," DePalma said.
this part of the scenario.
"When Mark came on board, he discovered a remarkable artifact – that the incoming seismic waves would have arrived from the point of impact at about the same time as the atmospheric duration of the ejection wave," DePalma said. "That was our big break."
The Dutch geologist Jan Smit carried out tests on the teasites of the Tanis site and confirmed that they are due to the extinction of the KT.
Some of the tektites were embedded in amber, and some were embedded in fossilized fish gills. "That's an amazing fact," said Smit. "That means the first direct victims of the impact are these clusters of fish."
The researchers suggest that the last act of mass killing of KT began when the hail of tektites triggered widespread forest fires and killed many of the creatures that survived the first shock.
The exact location of the Tanis site is kept secret to protect it from manipulation. "We went 40 years before something similar emerged that may be unique," said Smit. "So we have to be very careful with this place as we dig it up and learn from it."
<p class = "canvas-atom canvas-text Mb (1.0em) Mb (0) – sm Mt (0.8em) – sm "type =" text "content =" Update for 8:40 pm PT March 29: The study was skeptical even before its official publication, as palaeontologist Kenneth Lacovara notes Revised report to be more cautious: Here are a few tweets to help get you started on the Twitter threads: "data-reactid =" 116 "> Update for 8:40 pm PT March 29: The study was skeptical even before its official publication, as paleontologist Kenneth Lacovara points out on Twitter. That is why we have revised the title of this report. Here are a few tweets to get you started on the Twitter threads:
I spent the entire day lecturing at a storytelling conference. In the meantime, @laelaps and @SteveBrusatte have made additional comments on the new K / Pg paper in this thread. (Actually on the already published but not yet published K / Pg paper.) Https://t.co/ejVuFquYsq[19659036-KennethLacovara(@kenlacovara) March 30, 2019
There That's so suspicious via this @NewYorker story that my bullshit alarm sounds with full force. @SteveBrusatte is already here, but wow … this is someone with a heavy case of Bakkeritis trying to accelerate the glory. https://t.co/MQKF4ELLFN[19659036-Riley🏴☠️SkeletonKeys!(@Laelaps) March 29, 2019
Arrange for @Laelaps . I have read the PNAS paper and the supplement. Cool geology, credible story of a disaster at or near the K-Pg border, but there's no dinosaur cemetery in the paper at all. Only * a * fragmentary * dinosaur bone is mentioned. Very strange …
– Steve Brusatte (@SteveBrusatte) March 29, 2019
<p class = "Canvas Atom Canvas Text Mb (1.0em) Mb (0) – sm Mt (0.8em. )) – sm "type =" text "content =" In addition to DePalma, Richards, Alvarez and Smit, the authors of the study in the Proceedings of the National Academy of Sciences, "Prelude to extinction: A Seismically Induced Onshore Surge Deposit at the KPG border in North Dakota, "conclude David Burnham, Klaudia Kuiper, Philip Manning, Anton Oleinik, Peter Larson, Florentin Maurrasse, Johan Vellekoop, and Loren Gurche with Washington and the University of Kansas: Find a detailed account of DePalma's work You in this article from The New Yorker. "data-reactid =" 120 "> Besides DePalma, Richards, Alvarez and Smit, the authors of the study in the Proceedings of the National Academy of Sciences," Prelude to Extinction: A Seismically Induced Onshore. "Surge Deposit at the KPG border in North Dakota, "including David Burnham, Klaudia Kuiper, Philip Manning, Anton Oleinik, Peter Larson, Florentin Maurrasse, Johan Vellekoop, and Loren Gurche." This report is based on information from UC-Berkeley, the University of Washington and the University of Kansas. For a detailed account of DePalma's work, see this article by The New Yorker.