The asteroid responsible for the extinction of the dinosaurs was probably not an ordinary space rock. A new analysis indicates that it belonged to an extremely rare family of meteorites, the CO-type carbonaceous chondrites.
This precision tells us about the origin of the projectile and the mechanisms of the catastrophe that occurred 66 million years ago.
Artist's view of the meteorite crashing into Earth.
Donald E. Davis — NASA
The team studied a thin layer of clay deposited in several regions of the world after the impact. This geological level preserves a small part of the elements from the projectile, despite the almost complete vaporization of the asteroid during its collision with Earth.
The researchers used very precise measurements of nickel isotopes. These variants of the same element have slightly different masses. Their proportion forms a kind of chemical signature, which allows comparing the impact residues with the different known families of meteorites.
The result points to a CO-type carbonaceous chondrite as the most likely origin. These objects are among the most primitive materials in the Solar System. They also represent a very small fraction of the carbonaceous meteorites currently identified on Earth.
Remnant of the Cretaceous-Paleogene impact.
Dark, clay-rich KT boundary layer at Stevns Klint, Denmark, used in this study.
Credit: Dr. Philippe Claeys.
The asteroid was probably between 10 and 15 kilometers in diameter. It struck the region of what is now the Yucatán Peninsula in Mexico at an estimated speed of about 64,000 kilometers per hour. The impact formed the Chicxulub crater, now buried under rocks and sediments.
This composition also provides an indication of what favored the extinction. CO chondrites contain less sulfur and volatile elements than other carbonaceous meteorites. Global cooling would therefore have been more linked to the dust thrown into the atmosphere than to the sulfur contained in the asteroid.
The study does not yet allow us to determine with certainty the origin of this projectile. It could come from a remote region of the Solar System rich in rocky debris, or from the outer part of the asteroid belt located near Jupiter.