Dust From Asteroid That Ended Dinosaur Reign Closes Case on Impact Extinction Theory

Having dominated the planet's surface for hundreds of millions of years, dinosaur diversity came to a dramatic conclusion some 66 million years ago at the hot end of an asteroid impact with what is today Mexico's Yucatán Peninsula.

It's a theory so swollen with data that it's hard to imagine any room for doubt remains that this is indeed what happened. Were it a cold case, it'd be rubber-stamped and filed under 'Solved' by now.

But scientists are a nitpicky bunch, and a tiny gap in the chain of evidence linking signs of a global apocalypse with the scene of the crime has been begging to be closed.

An international team of researchers collaborating on a study of material from the Yucatán Peninsula's famous Chicxulub impact crater has finally matched the chemical signature of meteoritic dust within its rock with that of the geological boundary representing the dinosaur extinction event.

It appears to be a clear sign that the thin blanket of dust deposited on Earth's crust 66 million years ago originated from an impact event at this very spot.

"We are now at the level of coincidence that geologically doesn't happen without causation," says geoscientist Sean Gulick from the University of Texas in the US.

Together with fellow geoscientist Joanna Morgan from Imperial College London, Gulick led an expedition in 2016 to retrieve a sample of shattered rock from more than half a kilometre into the crater's peak ring.

Four different laboratories carried out measurements on the sample. The results not only help unite a major transition in the fossil record with the site, they also hint at a timeline that supports a rapid drop in dinosaur populations over as little as a decade or two.

"If you're actually going to put a clock on extinction 66 million years ago, you could easily make an argument that it all happened within a couple of decades, which is basically how long it takes for everything to starve to death," 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 the geological record was an open one. Whatever was responsible for the sudden loss of 75 percent of life on Earth, it had to be relatively quick, and global.

Hypotheses of such cataclysmic violence were mostly centred on two possibilities – one emerging from underground as a surge of volcanic activity, the other from above in the form of a comet or asteroid strike radically disrupting global climate. Read the free article.