Giant Asteroid Impact Dated--Precisely--To Dinosaurs' End
Asteroid Impact NASANew evidence settles a troubling discrepancy in the timeline of events that led to Earth's last great mass extinction. A couple of years ago, an international team of researchers got together to decide, once and for all, whether or not an asteroid crashed into Earth 66 million years ago and, if so, whether the impact would have been catastrophic enough to end the age of the dinosaurs and wipe out 75 percent of all life on the planet. After reviewing the evidence, which included radioisotope dates from the fossil record and scattered impact debris, as well as measurements of a 100-mile-wide crater in the Gulf of Mexico--the researchers concluded that the answer was yes, to both questions. But that didn't settle the matter entirely. Some scientists pointed to evidence of volcanism, climate change, or other potential causes for the dinosaurs' demise; others weren't convinced that the two events--impact...