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Dinosaurs died off about 33,000 years after an asteroid hit the Earth, much sooner than scientists had believed, and the asteroid may not have been the sole cause of extinction, according to a study released Thursday.
The theory that the dinosaurs' extinction about 66 million years ago was linked to an asteroid impact was first proposed in 1980. The biggest piece of evidence was the so-called Chicxulub (pronounced "cheek'-she-loob") crater off the Yucatan coast in Mexico.
It is believed to have been formed by a six-mile-(9.6-km-) wide object that melted rock as it slammed into the ground, filling the atmosphere with debris that eventually rained down on the planet. Glassy spheres known as tektites, shocked quartz and a layer of iridium-rich dust are still found around the world today.
About 1 million years before the impact, Earth experienced six abrupt shifts in temperature of more than 2 degrees in continental mean annual temperatures, according to research cited by Renne and his co-authors.
The temperature swings include one shift of 6 to 8 degrees that happened about 100,000 years before the extinction.