Scientists first proposed the asteroid impact theory of dinosaur mass extinction 30 years ago. The discovery of a massive crater at Chicxulub [CHICK-shuh-loob], in Mexico's Yucatán Peninsula in 1991, strengthened that hypothesis. The Chicxulub crater is more than 120 miles wide and scientists believe it was created when an asteroid more than six miles wide crashed into Earth 65 million years ago.
The cataclysmic impact—a million times more powerful than the largest nuclear bomb ever tested—triggered massive earthquakes, atmospheric discharge and oceanic upheaval. The ensuing mass extinction ended both the reign of the dinosaurs and the Cretaceous period, which gave way to the Paleogene period. This theory, having steadily accumulated evidence, was thought to be a near-consensus view.
Recently, however, in a series of articles, researchers posed an alternate hypothesis for the mass extinction. Some scientists claim that long-term volcanic activity at the Deccan Traps, in what is now India, caused acid rain and global cooling, gradually making life untenable for the dinosaurs and other large animals. They also suggest that the Chicxulub impact occurred some 300,000 years before the mass extinctions.
The alternate hypothesis spurred Chicxulub impact proponents to respond. The current Science article dispels the Deccan Traps hypothesis, arguing that the geological record favors the Chicxulub impact event theory.
Citation: Schulte et al., 'The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary', Science, 2010; doi:10.1126/science.1177265