It was a combination of calamities — an asteroid strike followed by vast volcanic eruptions half a world away — that doomed the dinosaurs and many other creatures 66 million years ago.

That is the conclusion of scientists who said on Thursday they have determined with new precision the proximity of the dates of these catastrophes: a space rock about 6 miles (10 kilometers) wide striking Mexico's Yucatan region and colossal eruptions in India.

The two events roiled Earth by throwing dust, ash and harmful fumes like carbon dioxide and sulfur dioxide into the air, altering the climate and killing off about 75 percent of all species in one of Earth's worst mass extinctions.