Ruthenium isotopes show the Chicxulub impactor was a carbonaceous-type asteroid

Area of Science:

• Geochemistry
• Planetary Science
• Paleontology

Background:

• The Cretaceous-Paleogene boundary, marked by an impact layer 66 million years ago in Chicxulub, Mexico, shows elevated platinum-group elements like ruthenium.
• Understanding the origin of impactors is crucial for reconstructing Earth's history and planetary evolution.

Purpose of the Study:

• To determine the origin of the Chicxulub impactor and other impact events by analyzing ruthenium isotopes.
• To investigate the composition of asteroids impacting Earth throughout its history, including early accretion stages.

Main Methods:

• Ruthenium isotope measurements were performed on samples from three Cretaceous-Paleogene boundary sites.
• Isotopic analysis was conducted on samples from five other impact structures (36 to 470 million years old).
• Samples from ancient 3.5-billion- to 3.2-billion-year-old impact spherule layers were also analyzed.

Main Results:

• The Chicxulub impactor exhibited isotopic signatures consistent with a carbonaceous-type asteroid formed beyond Jupiter's orbit.
• Five other impact structures showed isotopic signatures more aligned with siliceous-type asteroids, originating closer to the Sun.
• Ancient impact spherule layers indicated carbonaceous-type asteroid impacts during Earth's final accretionary phases.

Conclusions:

• The Chicxulub impactor's origin has been identified as a carbonaceous asteroid from the outer solar system.
• Asteroid compositions varied significantly based on their formation location and the timing of Earth impacts.
• Ruthenium isotope analysis provides a powerful tool for tracing the provenance of extraterrestrial material throughout Earth's history.