The meteorite that struck Earth approximately 66 million years ago, triggering the extinction of 75 percent of all species—including non-avian dinosaurs—was a rare type of carbonaceous chondrite, a class of rocks that are themselves scarce. A team led by the University of Paris has published in Science Advances the results of an advanced nickel isotope analysis of samples to determine the composition of the deadly Cretaceous-Paleogene meteorite.

The study points to a carbonaceous chondrite of the Ornans class, which "do not resemble the typical meteorites found in museum collections at all," according to Philippe Claeys of the University of British Columbia in Canada, one of the study's co-authors.

A CO Chondrite, a Cosmic Rarity

Carbonaceous chondrites account for only five percent of meteorites from which samples have been recovered on Earth, and Ornans-class chondrites (CO chondrites) represent a minuscule fraction of that group. "The fact that they were hit by such a rare and distant projectile really highlights how unlucky the dinosaurs were," Claeys said in a university statement.

The Impact That Formed Chicxulub

The body that caused the impact was between 10 and 15 kilometers in diameter and struck at an estimated speed of 64,000 kilometers per hour, forming the Chicxulub crater in Mexico. The researchers measured nickel isotopes in marine clays collected over several years from a thin layer of that material formed across the planet as a result of the impact, since the meteorite was completely vaporized upon collision.

A CO chondrite, which ranks among the most primitive, unaltered materials in the solar system, contains far fewer volatile elements—such as carbon, zinc, water, and particularly sulfur—than other types of meteorites discovered on Earth to date.

Where Did the Meteorite Come From?

Questions remain regarding the meteorite's origins, although it may have come from the distant, debris-rich regions of the outer solar system or the outer region of the asteroid belt near Jupiter.