Science. Dinosaurs’ rule on Earth ended in spring

Now it’s known: With the collapse of a giant asteroid some 66 million years ago, the dinosaur rule on Earth ended … in the boreal spring, according to a study published Wednesday. Study lead author Melanie During told a press briefing on Tuesday that this season’s determination is key to helping to understand “how to survive and then thrive”.

We will never know, on such a time scale, the exact year of the event, which occurred at Chixulub on the present-day Yucatan Peninsula in Mexico. According to a recent study the impact of an asteroid, or perhaps a fragment of a comet, caused a series of disasters following the climate upheaval. They marked the end of the Cretaceous era and its masters on land, non-avian dinosaurs, and in the air, pterosaurs, flying reptiles.

key light

The team, led by paleontologist and doctoral student Melanie During and vertebrate expert Dennis Voeten at the Swedish University of Uppsala, sheds important light on this phenomenon with their study of fish fossils.

The site of Tanis in the present-day US state of North Dakota perpetuates the memory of this apocalypse. This fossil brings together populations of species, most of which found themselves buried beneath deposits of “sech,” a type of tidal wave, reports the study. In this event, the shock waves of the earthquake traveled more than 3,000 km in a few tens of minutes, and lifted the waters of an inland ocean, which then crossed present-day America, sweeping all life in their path.

study of sturgeon lives

In Tanis, scientists studied the remains of three sturgeon and three paddlefish, using high-resolution X-ray tomographic analysis exclusively from the European Synchrotron of Grenoble (ESRF). He established for the first time that the fish was actually destroyed in the Seich episode, which was accompanied by a shower of glass balls, an actual deluge of sand from the heat of the impact and projected into the air, before falling back to the ground. Distances. During Melanie, the fish died “within 15 to 30 minutes” after the impact. The evidence was that it had swallowed enough water for the ESRF device to identify the gills in their gills, but not enough to move them into their digestive tract.

At the ESRF, a microscopic study of the bone formation of fossils made it possible to determine that this formation, which occurs in an annual growth cycle, was at the first stage of a new cycle. “Bone cells were relatively small, but they were starting to grow again, which coincides with spring,” Dennis Woten explained at the press briefing. The finding, confirmed by analysis of the concentration in bones of an isotope of a carbon molecule, increases according to the richness of the planktonic diet, which is also seasonal. “The fish died in the spring and the reign of the dinosaurs ended in the spring,” ends during Melanie.

a “nuclear” winter

The impact, with a power equivalent to at least several billion nuclear bombs off Hiroshima, had consequences for the entire planet. Immediately, with the destruction of all life nearby and huge fires at great distances. And in the long term, provoking a “nuclear” winter for years: Heavy extraction of sulfur and dust created aerosols in the atmosphere, causing acid rain and blocking the Sun’s rays, thus reducing photosynthesis.

Plant diebacks ate a vegetarian diet like large sauropod dinosaurs. Scientists believe the disaster affected the fauna of the Northern Hemisphere more severely than those in the South in the full spring phase of reproduction and development, with some species entering a phase of rest and hibernation. . , This event caused “selective extinction”, according to Melanie During, who conceives that “to survive a nuclear winter you would have to survive the first impact, and this probability was greater for those who could hibernate”. “. In this regard, the study notes that ecosystems in the Southern Hemisphere recovered more quickly from the disaster than those in the North.

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