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Having dominated the planet’s surface for hundreds of millions of years, the diversity of dinosaurs came to a dramatic conclusion some 66 million years ago at the peak of an asteroid impact with what is today the Yucatán Peninsula in Mexico.
It’s such a data-packed theory that it’s hard to imagine that there is any room for doubt that this is what happened. If this was an unresolved case, it would now be stamped and filed under “Resolved”.
But scientists are a picky bunch, and a tiny gap in the chain of evidence connecting signs of a global apocalypse to the crime scene has demanded to be filled.
An international team of researchers collaborating on a study of materials from the famous Chicxulub impact crater on the Yucatán Peninsula finally matched the chemical signature of the meteor dust in its rock with that of the geological boundary representing the event of extinction of dinosaurs.
This seems to be a clear sign that the thin layer of dust deposited on the earth’s crust 66 million years ago came from an impact event at this very location.
“We are now at the level of a coincidence that does not occur geologically without causation,” says geoscientist Sean Gulick of the University of Texas in the United States.
Along with fellow geoscientist Joanna Morgan of Imperial College London, Gulick led an expedition in 2016 to retrieve a sample of broken rock over half a kilometer from the crater ring.
Four different laboratories performed measurements on the sample. The findings not only help unite a major transition in the fossil record with the site, but they also suggest a timeline that supports a rapid decline in dinosaur populations over as little as a decade or two.
“If you were going to put a clock on extinction 66 million years ago, you could easily argue that it all happened in a few decades, which is basically the time it takes for anything to die of. hungry, ”Gulick says.
Half a century ago, the question of why the diversity of fossils representing the Mesozoic era ended so abruptly in the geological record was open. Whatever the cause of the sudden loss of 75% of life on Earth, it had to be relatively rapid and global.
The assumptions of such cataclysmic violence centered primarily on two possibilities – one emerging from the subsoil as a surge of volcanic activity, the other from above as a comet or of an asteroid radically disrupting the global climate.
In 1980, American physicist Luis Alvarez and his son, a geologist named Walter, published a study of a thin layer of sediment separating the dinosaur-populated Cretaceous period from the post-dinosaur world of the Paleogene.
A defining feature of this thin strip of sedimentary rock, millimeter to centimeter thick, was an unusually high amount of the element iridium, a metal that is not found in abundance in the earth’s crust.
One place where you will find a lot of iridium is in meteorites. The discovery of Alvarez and his son was therefore the first solid evidence that something from space splashed its remains all over the planet as dinosaur biodiversity plunged.
Coincidentally, the site of this colossal collision was the subject of ongoing research around the same time, while also establishing a clear link between the 180-200 kilometer-long (112-125 mile) scar at the southern limit of the gulf. of Mexico with the killer asteroid would not occur until the 1990s.
Since then, the evidence supporting an asteroid impact has only grown stronger, with models going so far as to suggest that the angle, as well as the location of the Chicxulub impact, has played a crucial role in the scale of the extinction event.
Signs that an area of intense geologic activity in western India called Deccan Traps at the time provided large amounts of greenhouse gases meant that the volcano hypothesis was never entirely ruled out, at least as a possible contributing factor.
Whether this tectonic hotspot played a role in the famous extinction event, or even helped biodiversity recover afterwards, is still up for debate.
What is no longer a matter of serious discussion is whether the 12-kilometer-wide chunk of rock that struck off what is now Mexico about 66 million years ago is the same who sprinkled the remains of countless dinosaurs.
“The circle is finally over,” says Steven Goderis, head of the study, geochemist at the Vrije Universiteit Brussel in Belgium.
Case closed.
This research was published in Scientific advances.
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