Evidence that the impact of a kilometers-wide asteroid ravaged Earth's ecosystems and wiped out the dinosaurs millions of years ago is now stronger than ever. Using a high-resolution dating technique that measures the ratios of two argon isotopes, researchers analyzed 14 samples of material that had been flung from the impact site just north of the Yucatán Peninsula. Those dates, when combined with similar analyses reported previously, pin down the event—dubbed the Chicxulub impact after a small Mexican village closest to the offshore impact site—to approximately 66,038,000 years ago. And argon-argon dating of volcanic ash samples unearthed in Montana (image) from a bed of coal lying just a few centimeters above the iridium-rich layer deemed to contain fallout from the asteroid impact—and just 5 cm above rocks containing large amounts of dino-era pollen—suggests that mass extinctions occurred about 66,043,000 years ago. Considering the statistical errors in the two analyses, the impact and the dino die-offs may have occurred at the same time, or they may have occurred no more than 32,000 years apart, the researchers report online today in Science. Regardless, the team says, the new results certainly knock a hole in the notion that the mass extinctions, including the dinosaurs, occurred as much as 300,000 years before the asteroid impact, which some other researchers have contended for decades.
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