After dominating the planet’s surface for hundreds of millions of years, dinosaur diversity came to a dramatic conclusion about 66 million years ago, at the hot end of an asteroid impact with what is now the Yucatan Peninsula of Mexico.
It is a theory so inflated with data that it is hard to imagine that there is any doubt that it happened. If it were a cold case, it would be stamped and archived under “Solved” so far.
But scientists are a huge pile and a small gap in the chain of evidence linking the signs of a global apocalypse to the crime scene has called for it to be closed.
An international team of researchers collaborating on a study of material from the famous impact crater in the Yucatan Peninsula has finally associated the chemical signature of meteorite dust in its rock with that of the geological boundary that represents the event of the extinction of dinosaurs.
It 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 right here.
“We are now at a level of coincidence, which geologically does not happen without causation,” says geologist Sean Gulick of the University of Texas in the United States.
Together with his geo-scientific colleague Joanna Morgan from Imperial College London, Gulick led an expedition in 2016 to take a sample of crushed rock from more than half a kilometer in the crater’s top ring.
Four different laboratories performed measurements on the sample. The results not only help to unite a major transition in fossil records with the site, but also indicate a chronology that supports a rapid decline in dinosaur populations in just a decade or two.
“If you actually set a time of extinction 66 million years ago, you could easily argue that it all happened in a few decades, which is practically how long it all takes to starve,” says Gulick.
Half a century ago, the question of why the diversity of fossils representing the Mesozoic era came to such an abrupt end in geological records was an open one. Whatever was responsible for the sudden loss of 75 percent of life on Earth had to be relatively fast and global.
Hypotheses of such cataclysmic violence have largely focused on two possibilities – one coming out of the ground as an increase in volcanic activity, the other from above in the form of a comet or asteroid strike that radically disrupts the global climate.
In 1980, the American physicist Luis Alvarez and his son, a geologist named Walter, published a study of a thin layer of sediment that divides the Cretaceous period populated by dinosaurs from the post-dinosaur world of the Paleogene.
A defining feature of this thin strip of sedimentary rock, with a thickness of millimeters to centimeters, was an unusually large 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. So the discovery of Alvarez and his son marked the first solid proof that something in space scattered his remains all over the planet when the biodiversity of the dinosaurs sank.
Coincidentally, the site of that colossal collision was at the center of ongoing research at the same time, although it made a clear link between 180- to 200-kilometer (112 to 125-mile) scars on the southern edge of the Gulf of Mexico with the killer asteroid no. it would happen until the 1990s.
Since then, the evidence in support of an asteroid impact has become stronger, with models going so far as to suggest the angle, as well as the location of the Chicxulub impact, have played a crucial role in the magnitude of the disappearance event.
Signs that an area of intense geological activity in western India, called the Deccan Traps, was contributing to large amounts of greenhouse gases at the time meant that the volcano hypothesis was never completely ruled out, at least as a possible contributing factor.
Whether this tectonic hot spot played a role in the famous extinction event or even helped biodiversity to recover after it is still under debate.
What is no longer a serious point of discussion is whether the 12-kilometer-wide piece of stone that struck off the coast of what is now Mexico about 66 million years ago is the same one that dusted the remains of countless dinosaurs. .
“The circle is now finally complete,” says study leader Steven Goderis, a geochemist at the Vrije Universiteit Brussel in Belgium.
Case closed.
This research was published in Scientific advances.