There is no doubt that the main cause of the disappearance of the dinosaurs is due to the fall of a small celestial body on the Yucatan. The precise date is intended to remain unclear, we only know that it happened around 66 million years ago. You would think that the same would apply to determining the season of the event. Remarkably, it does not appear to be the case!
You will also be interested
[EN VIDÉO] Interview: is the mystery of the dinosaurs extinction finally solved? Scientists have always struggled to find a consensus explaining the extinction of dinosaurs. Even though the most widely accepted theory is that of a meteorite, gray areas still persist today. Futura-Sciences interviewed Éric Buffetaut, paleontologist, to enlighten us on the question.
As the video below explains with a lot of information, it has been almost 40 years since Walter Alvarez, then a young geologist fresh out of the University of Berkeley, started a revolution in the sciences of Earth by first discovering a strange stratum dark clay marking the sudden disappearance of plankton sailor, precisely at the end of the Cretaceous and at the beginning of the Tertiary era. However, it is at this time that not only disappeared large marine reptiles, the ammonites and the Belemnites, but especially the dinosaurs.
Joining his father, the Nobel laureate of physical, Luis Alvarez, and especially to chemists Frank Asaro and Helen Michel, all from UC Berkeley, he undertook to make the layer speak by dating it and analyzing it precisely. The researchers found that this stratum contained an unusually high amount of a rare element on the Earth’s surface, theiridium. This metal is, on the other hand, quite abundant in comets and the asteroids ; This is why Walter Alvarez came to propose that the biological crisis which occurred 66 million years ago, the famous Cretaceous-Tertiary crisis (or KT, from German Kreide-Tertiär), was due to the fall of a small celestial body on Earth. the weather and the sunstroke would have been changed, causing the food chain.
This thesis has since been broadly verified, although it is also believed that the volcanoes originally the basaltic plateaus (the traps) of the Deccan, in western India, have also played their part. What is certain is that a large impact crater was found precisely correlated with the deposition of the layer ofclay black. This is of course theastroblem of Chicxulub.
Almost 40 years ago, scientists discovered a layer of iridium spread over our planet, proof of a cosmic impact on the Earth’s surface. Take a look back at an incredible investigation that brought to light the evidence of a mass extinction 66 million years ago. Lecturer-researcher at the Paris-Sud Geosciences laboratory of the University of Paris-Saclay, Sylvain Bouley deciphers planetary surfaces in order to reconstruct the history of our solar system. © Fleurance Astronomy Festival
A snapshot of the late Cretaceous
Today, researchers from the Florida Atlantic University (FAU) in the USA, at the head of an international team of specialists in geosciences, have achieved an extraordinary feat: determining the season of the death of dinosaurs in the Northern Hemisphere. The method used is explained in an open access article from Scientific Reports. A press release from the FAU gives some explanations provided in particular by Robert DePalma, main author of the article.
the paleontologist and geologist reminds us that ” the time of year plays an important role in many biological functions such as reproduction, feeding strategies, host-parasite interactions, seasonal dormancy, and reproductive patterns. Therefore, it is not surprising that the time of year when a global hazard occurs can play an important role in the gravity of its impact on life. The seasonal schedule of the impact of Chicxulub has therefore been a question whose answer is critical to the history of the Late Cretaceous extinction. So far, the answer to this question has remained unclear. “.
Robert DePalma therefore studied with his colleagues the Tanis site in present-day North Dakota. 66 million years ago, Tanis was on the edge of a south-to-north basin in which the water of a marine transgression engulfed, creating the famous Niobraran Sea, also known as the Western Interior Seaway (Western Interior Seaway). It is representative of the Hell Creek Formation which is made up of various sediments ( sandstone slightly indurated, clayey and mudstones) deposited in a medium of fresh water or brackish associated with streams and deltas.
Robert DePalma on the Tanis site. © KU News Service
Frozen seasonal clocks
What Robert DePalma and his colleagues have already shown, a few years ago, is that we find on this site a sedimentary layer of one and a half meters thick deposited in the bed of a river. This layer contains many Pisces ofpure water stacked on top of each other but mixed with ammonites and micro-organisms sailors called dinoflagellates with impressive amounts of tektites, these droplets of molten rock from the Earth’s crust. Now we know that tektites are produced by the impact of a large celestial body. Finally, the dating of the argillaceous layer containing iridium surmounting that where this veritable cemetery is located coincides precisely with the dating of the impact of Chicxulub.
Clearly, this is the snapshot of the death of these living organisms, when the tsunami caused by the impact of the asteroid moved up the Niobraran Inland Sea until it also raised the river, which explains why this curious mixture of freshwater fish with marine organisms.
Studying fish populations fossils very well preserved turned out to be very interesting. Indeed, much like tree rings, growth structures in the bones of some fish are sensitive to the season of the year. Based on the characteristics of modern fish, we also know in which season they are born and at what rate they grow, and therefore what size they reach in a given season.
In both cases, the sudden death of the fish in a way freezes the clocks which therefore make it possible to determine the season of their death. It appears today, with two almost independent dating methods, and above all concordant, that the impact of Chicxulub arrived at the moment when the northern hemisphere was going to pass from spring to summer.
Interested in what you just read?
.
fs11