In the 1978 a giant crater was discovered on the Yucatan peninsula next to Chicxulub, Mexico. 35 years later we have real evidence to show that the impact coincided with the extinction of the dinosaurs.
Data shows that the impact matches to within 32,000 years of the dinosaurs extinction. This is contrasted with previous studies that estimated the demise 300,000 years earlier—which is why some had maintained that other causes could have wiped out the dinosaurs.
Thanks to some clever radiometric dating of debris near the crater they are convinced that the 100+ mile crater caused an extremely long winter that killed the dinosaurs. For a visualization of the event see the video below.