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每日英語跟讀 Ep.K430: The Dinosaur Age May Have Ended in Springtime
The dinosaur-killing meteor hit in spring.
That is the conclusion of scientists who examined the bones of fish that died on that day when a 6-mile-wide asteroid collided with Earth.
“These fishes died in spring,” said Melanie During, a graduate student at Uppsala University in Sweden and lead author of a paper published in the journal Nature. “The reign of dinosaurs ended in spring.”
Scientists have known when the meteor hit — just over 66 million years ago, give or take 11,000 years — and where it hit, off the Yucatán Peninsula of Mexico. That ended the Cretaceous period of Earth’s geological history, but even though three-quarters or more of the species of plants and animals disappeared in the mass extinction that followed, it has been hard to pinpoint fossils of anything directly killed by the meteor.
But in 2019, paleontologists published the discovery in southwestern North Dakota of what appeared to be a mass graveyard of creatures that died hours or days after the impact. Although North Dakota was about 2,000 miles from where the meteor hit, the seismic waves of what was the equivalent of an earthquake with a magnitude of 10 or 11 sloshed water out of the lakes and rivers and killed the fish. Tektites — small glass beads propelled into the air by the impact — rained from the skies.
The researchers spent years exploring the site, known as Tanis, which is in the fossil-rich Hell Creek formation that stretches across four states.
With the new science results, the fossils now provide insight into the cataclysm that was previously impossible to discern.
“It’s amazing that we can take an event, a single moment that happened 66 million years ago — literally a rock falling down and in an instant striking the Earth — and we can pinpoint that event to a particular time of the year,” said Stephen L. Brusatte, a paleontologist at the University of Edinburgh who was not involved in the research. “I think it’s a detective story of the highest caliber.”
Animals in the Northern Hemisphere — some emerging from hibernation or giving birth to young — might have been more vulnerable to extinction. “If it was spring, then it was not very likely for many organisms to be in hibernation,” During said.
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