...the prevailing theory:
Current theory:
The rocky object that wiped out the dinosaurs 65 million years ago may have been a comet, rather than an asteroid, scientists say.
The 112-mile (180 kilometers) Chicxulub crater in Mexico was made by the impact that caused the extinction of dinosaurs and about 70 percent of all species on Earth, many scientists believe. A new study suggests the crater was probably blasted out by a faster, smaller object than previously thought, according to research presented this week at the 44th Lunar and Planetary Science Conference in The Woodlands, Texas.
Evidence of the space rock's impact comes from a worldwide layer of sediments containing high levels of the element iridium, dubbed the Cretaceous-Paleogene (K-Pg) boundary, which could not have occurred on Earth naturally.
The new research suggests the often-cited iridium values are incorrect, however. The scientists compared these values with levels of osmium, another element delivered by the impact.
Their calculations suggested the space rock generated less debris than previously thought, implying the space rock was a smaller object. In order for the smaller rock to have created the giant Chicxulub crater, it had to have been going exceedingly fast, the researchers concluded.
Huffington Science: New Study Suggests Comet Instead Caused Extinction Event
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