Almost 66 million years ago, a Chicxulub asteroid hit the Earth at the boundary between the Cretaceous and Paleogene eras (K-Pg boundary). The collision was so devastating that it caused mass extinction and wiped out almost all the dinosaurs and many other species.
Now, scientists have pinpointed the origin and composition of the Chicxulub impactor. Their findings revealed that Chicxulub impactor was a carbonaceous-type asteroid that originated beyond Jupiter.
To determine what the object was and where it came from, scientists obtained samples of K/Pg rocks from three sites and compared them with rocks from eight other impact sites from the past 3.5 billion years.
In particular, scientists evaluated ruthenium (Ru) isotopes in samples from the K-Pg boundary. They also compared samples from five other asteroid impacts, samples from the last 541 million years, samples from ancient Archaean-age (3.5 – 3.2 billion-years-old) impact-related spherule layers, and samples from two carbonaceous meteorites.
The Ru isotope signatures in samples from the K-Pg boundary were the same as those in carbonaceous chondrites (CCs), not Earth or other meteorites. This suggests that the Chicxulub impactor likely came from a C-type asteroid that formed in the outer Solar System.
The findings also rule out a comet as the impactor. Ancient Archean samples show that impactors had a CC-like composition, suggesting they came from the outer Solar System and might have hit Earth during its final stages of formation. In contrast, impact sites from other times showed Ru isotope compositions that match S-type asteroids from the inner Solar System.
Journal Reference:
- Mario Fischer-Godde, Jonas Tusch et al. Ruthenium isotopes show the Chicxulub impactor was a carbonaceous-type asteroid. Science. DOI: 10.1126/science.adk4868