The day the dinosaurs became extinct. Fossils of the first victims of the asteroid impact
Excavations in North Dakota have revealed a burial ground of animals, fish and plants that were annihilated, according to paleontologists, shortly after the impact of an asteroid 66 million years ago. It is assumed that this impact led to the extinction of the dinosaurs.
The beginning of the end began with violent tremorsów, whichóre aroused gigantic waves on the waters of the Middle Eastódląd sea, from whichórym bordered areas of the present PóNorth Dakota. Then a rain of tiny, hot debris fell from the skyów, whoóre likely to have set most of the vegetation on land on fire.
Then came a huge, more than 30-meter wave, która threw fish far inland and for a while reversed theóIt cut the course of a river flowing into the sea. Fish, które survived this, they were constantly bombarded with a rain of hot debrisów. After 10-20 minutes, a second tidal wave flooded the shore and covered the dead or dying creatures with gravel, sand and fine sediment, creating over them a tomb shielded from the outside world for the next 66 millionów years.
This is the scenario of events presented by scientists, któers discovered this unique burial ground – fossil deposit. Fish stacked on top of each other, mixed with scorched tree trunks, branches, dead mammals, mozasaur bonesów, insects, half of a triceratops, ammonites and other marine microorganisms – This is what the cemetery from Hell Creek Formation in PóNorth Dakota.
Paleontologist Robert DePalma has been excavating there since 2013. He is also the headównym author of publications on the subject, whoóra has just appeared in the pages of the journal „PNAS”. According to the scientist, this fossil deposit is a record of the day in which theórym the dinosaurs became extinct. Along with them, about three-quarters of the species became extinctóin plants and animals. The extinction was caused by a massive asteroid, whichóre hit the Earth 66 millionóyears ago and is called the Cretaceous extinction.
– No such collection, consisting of a large number of species, can be found anywhere in the worldóin representing róThe age of the organismóin and in róThe different stages of life, from whichór which all died at the same time, on the same day – DePalma said. He added that the site shows what befell regions far from the impact site of the space rock.
DePalma affiliated with the University of Kansas, along with colleagues at the University of California, Berkeley, described the Hell Creek Formation burial ground in a publication and presented evidence linking it to an asteroid or comet, która hit the area of póhe Yucatan Peninsula and the Gulf of Mexico 66 millionów years ago. The impact created a huge crater on the ocean floor called Chicxulub. With the impact, huge amounts of dust were lifted into the airów. The cloud eventually surrounded the Earth, restricting the sun’s rays and lowering Earth’s temperatures ultimately causing the annihilation of 75 percent of the. Speciesów living inótime on our planet.
– It is like a museum of the end of the Cretaceous in a layer of póhe earthquake,” said Mark Richards, a professor emeritus at a California university whoóry is now a clergyman and professor at the University of Washington. Richards, whoóry, along with Walter Alvarez of the University of California 40 years ago, first advanced the hypothesis that a comet or asteroid impact caused a mass extinction, were asked by DePalma and his colleague Jan Smit to consult on a new publication of the. Researchers detailedólnstead, it was the so-called. tektites –tiny pieces of molten rock and tsunami-like waves.
Richards and Alvarez determined that the fish could not have been buried by a typical tsunami. They admitted that the falling tektites prevented the formation of muddy. The researchers said that the seismic waves to the studied extinction site probably reached within 10 minutes of the impact, whichóre would be the equivalent of an earthquake of magnitude 10 or 11 on the Richter scale. According to them, the resulting standing wave so-called. sejsza.
Photo. Robert DePalma/UC Berkeley
Photo. Robert DePalma/UC Berkeley
Although large earthquakes often produce seiches in confined bodies of water, these phenomena are rarely noticed. Researchers here pointed to the example of the strong 2011 Tohoku earthquake in Japan, whichóre caused the formation of nearly two-meter high standing waves 30 minutes póThen in a Norwegian fjord 8,000 kilometers awayów.
DePalma and his colleagues noted that someóre fish fossils contain tiny spherules – Tiny balls of enamel formed by the melting of a meteorite. Funnels from the particle bombardment can also be seen in the fossilized mud. As Alvarez stated, the rain of particles móheads have speeds as high as more than 300 k/h. Researchers believe that the hot debris rain was so intense that it ignited fires across the American continent, if not the entire world.
According to the publication, at least two giant seiches formed 20 minutes apart leaving behind thick sediments covering the fossils. These are layers of clay rich in iridium, a rare metal on Earth but common in asteroids and comets. This layer is known as the K-T boundary – Cretaceous-Tertiary boundary – A layer separating Cretaceous and Paleogene sediments.
In 1979, Walter Alvarez and his father Luis Alvarez (winner of the 1968 Nobel Prize in Physics) were the first to recognize the importance of iridium layers at the K-T boundary. They proposed the hypothesis that higher concentrations of iridium were created by the impact of a comet or asteroid on Earth and this event is responsible for the Cretaceous extinction.
The impact melted the bedrock beneath the seafloor and pulverized the asteroid, sending dust and molten rock all the way into the stratosphere, where winds spread them around theóHEAD OF THE PLANET. This shut out the sun’s rays for months, if not years. Debris fell from the sky: not only tektites, but also rock debris from the continental crust. The iridium-rich dust from the pulverized meteor was the last, whichóry precipitated out of the atmosphere after the impact, forming the K-T boundary and ending the Cretaceous period.
– When we proposed a hypothesis to explain the great extinction, it was based only on finding an anomalous concentration of iridium – the fingerprint of an asteroid or comet, Alvarez said. – Since then, the evidence has gradually increased. But it never occurred to me that we would find such a fossil deposit as this – added.
A key confirmation of the hypothesis was the discovery of the Chicxulub impact crater at the bottom of the Gulf of Mexico, whichóhe dating of which indicated the exact age of the mass extinction. The discovery of the fossil cemetery is the first thatóre contains the remains of animals, whichóre died as a result of the impact, as well as animals killed immediately after the impact.