At what time of year did the meteorite that wiped out the dinosaurs hit Earth?

The meteorite that 66 million years ago wiped out the dinosaurs It hit the Earth in the spring of the northern hemisphere, as revealed by the study of the fish bones that died just an hour after that brutal impact.

This research, carried out by an international team and published in Nature, helps explain the pattern of extinctions that followed and adds to the understanding of this crucial moment in Earth’s history.

The Chicxulub asteroid, which hit what is now the Yucatan Peninsula (Mexico), put an end to the Mesozoic era and, but it was also selective, since it wiped out non-avian dinosaurs, pterosaurs, ammonites and most marine reptiles. while mammals, birds, crocodiles and turtles survived.

Although it was known when and where the impact occurred, until now the season of the year was unknown and this new study suggests that it was in spring, a particularly sensitive time for the numerous species of the northern hemisphere,

Ecosystems in the southern hemisphere, which were hit during the fall, appear to have recovered up to twice as fast as those in the northern hemisphere, the authors note.

The study sheds light on the circumstances surrounding the diverse extinction of the different groups and the answers come from the fossils of the spines of sturgeons and paddle fish found at the paleontological site of Tanis (United States).

The impact shook the continental plate and, which mobilized large volumes of sediment that engulfed the fish and buried them alive, while the impact spherules (glass beads of terrestrial rock) rained down from the sky.

Fossils from the Tanis site in North Dakota were perfectly preserved, their spines showing almost no signs of geochemical alteration, filtered impact spherules still attached to their gills, and even some soft tissue preserved.

Through various tests, the scientists discovered that the fish spines registered a seasonal growth very similar to that of the trees, adding, explained Sophie Sánchez, from the University of Uppsala (Sweden).

The recovered growth rings “they captured the life histories of the fish and the last seasonality of the Cretaceous and, with it, the season in which the catastrophic extinction occurred”, said Jeroen van der Lubbe of the Free University of Amsterdam.

The distribution, shape and size of bone cells, which are also known to fluctuate with the seasons, provide

In this case, both cell density and volumes were increasing, but had not yet peaked during the year of death, implying, according to Dennis Voetem of Uppsala University, that “Growth stopped abruptly in spring.”

One of the paddlefish studied was subjected to stable carbon isotope analysis to reveal its annual feeding pattern. The availability of zooplankton, their preferred prey, fluctuated seasonally, peaking between spring and summer.

The carbon isotope signal in the fish’s growth record confirms that the feeding season had not yet peaked. , infers Melanie During, from Uppsala University.

Since the extinction must have started abruptly during the Northern Hemisphere spring, “We are beginning to understand that this event took place during particularly sensitive life stages of the organisms of the including the beginning of the reproductive cycles”he adds.

And since fall in the southern hemisphere coincides with spring in the north, the preparation for winter may have protected organisms in the southern hemisphere.

In general, it is known that organisms that were exposed died almost immediately. So those who took refuge in caves or burrows because they were hibernating were much more likely to survive in the Paleogene.

”This crucial finding –highlights– will help reveal why most dinosaurs died out, while birds and early mammals managed to avoid extinction.”

Agencies