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 end of an asteroid impact with the Yucatán Peninsula in Mexico.
This is a theory that is so swollen from data that it is hard to doubt that this is indeed what happened. If it was a cold case, it would now be placed with rubber stamp and filed under ‘Resolved’.
But scientists are a troublesome group, and a small gap in the chain of evidence linking signs of a global apocalypse to the scene of crime has begged to be closed.
An international team of researchers working together to study material from the famous Chicxulub impact crater on the Yucatán Peninsula has finally found the chemical signature of meteorite dust in its rock to match that of the geological boundary representing the extinction of the dinosaur.
This seems to be a clear sign that the thin dust blanket that was deposited on the earth’s crust 66 million years ago originated from an impact event at the same location.
“We are now at the level of coincidence that geologically does not happen without cause,” says geoscientist Sean Gulick of the University of Texas at the USA.
Together with fellow geoscientist Joanna Morgan from Imperial College London, Gulick led an expedition in 2016 to fetch a sample of more than half a mile into the crater’s peak circle.
Four different laboratories performed measurements on the sample. The results not only help unify a major fossil record transition with the site, but also point to a timeline that supports a rapid decline in dinosaur populations of about a decade or two.
“If you were to actually wipe out a clock 66 million years ago, you could easily argue that it happened within a few decades. That’s basically how long it takes before everything dies of starvation,” Gulick says.
Half a century ago, the question of why the diversity of fossils representing the Mesozoic era so abruptly came to an end in the geological report was an open question. Whatever was responsible for the sudden loss of 75 percent of life on earth, it had to be relatively rapid and global.
Hypotheses of such catastrophic violence were mostly centered on two possibilities – one that emerged underground as a surge of volcanic activity, and the other from above in the form of a comet or asteroid attack radically disrupting the world climate.
In 1980, the American physicist Luis Alvarez and his son, a geologist named Walter, published a study on a thin layer of sediment that divides the dinosaur-populated Cretaceous period of the post-dinosaur world of the Paleogene.
A defining feature of this millimeter to centimeter thick thin strip of sedimentary rock was an extraordinarily high amount of the element iridium, a metal that does not occur in abundance in the earth’s crust.
One place where you will find a lot of iridium is in meteorites. Alvarez and son’s discovery was thus the first solid evidence that something from space splashed its remains on the entire planet when dinosaur biodiversity plunged.
Coincidentally, the site of the colossal collision was the focus of continuous research at about the same time, although there was a clear link between the 180 to 200 kilometer long (112 to 125 miles) scar on the southern edge of the Gulf. of Mexico with the killer steroid would only happen in the nineties.
Since then, evidence in support of an asteroid impact has only grown stronger, with models going so far that the angle, as well as the location of the Chicxulub impact, played an important role in the extent of the extinction event.
Evidence that a zone of intense geological activity in the West Indies, called Deccan Traps, contributed large amounts of greenhouse gases at the time, means that the volcanic hypothesis has never been completely ruled out, at least as a possible contributing factor.
Whether this tectonic focal point played a role in the famous extinction event, or even the biodiversity thereafter helped to recover from it, can still be discussed.
What is no longer a serious point of discussion is whether the twelve-kilometer-wide rock that hit the coast of present-day Mexico about 66 million years ago is the same one that dusted off the remains of countless dinosaurs.
“The circle is now finally complete,” says study leader Steven Goderis, a geochemist from the Free University of Brussels in Belgium.
Case closed.
This research was published in Scientific progress.