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March 1, 2021 12:34 pm

Asteroid Dust Found in Crater Closes Case of Dinosaur Extinction

Phys.org shares an announcement from the University of Texas at Austin:Researchers believe they have closed the case of what killed the dinosaurs, definitively linking their extinction with an asteroid that slammed into Earth 66 million years ago by finding a key piece of evidence: asteroid dust inside the impact crater. Death by asteroid rather than by a series of volcanic eruptions or some other global calamity has been the leading hypothesis since the 1980s, when scientists found asteroid dust in the geologic layer that marks the extinction of the dinosaurs. This discovery painted an apocalyptic picture of dust from the vaporized asteroid and rocks from impact circling the planet, blocking out the sun and bringing about mass death through a dark, sustained global winter — all before drifting back to Earth to form the layer enriched in asteroid material that's visible today. In the 1990s, the connection was strengthened with the discovery of a 125-mile-wide Chicxulub impact crater beneath the Gulf of Mexico that is the same age as the rock layer. The new study seals the deal, researchers said, by finding asteroid dust with a matching chemical fingerprint within that crater at the precise geological location that marks the time of the extinction... The telltale sign of asteroid dust is the element iridium — which is rare in the Earth's crust, but present at elevated levels in certain types of asteroids... In the crater, the sediment layer deposited in the days to years after the strike is so thick that scientists were able to precisely date the dust to a mere two decades after impact. "We are now at the level of coincidence that geologically doesn't happen without causation," said co-author Sean Gulick, a research professor at the UT Jackson School of Geosciences who co-led the 2016 expedition with Joanna Morgan of Imperial College London... The dust is all that remains of the 7-mile-wide asteroid that slammed into the planet millions of years ago, triggering the extinction of 75% of life on Earth, including all nonavian dinosaurs.

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