A new isotopic study has pinpointed the Chicxulub meteorite as a rare CO chondrite. This finding challenges previous assumptions about its composition and origin. The discovery could reshape our understanding of the mass extinction event.
The meteorite that struck the Yucatán Peninsula 66 million years ago, triggering the extinction of the dinosaurs, has now been identified as one of the rarest types in the Solar System. According to a study published in 'Science Advances', advanced nickel isotope analysis has revealed that the Chicxulub impactor was a CO chondrite—a class of meteorite found in only a tiny fraction of known samples.
For decades, scientists have debated the exact nature of the object responsible for the mass extinction at the Cretaceous-Paleogene boundary. While it was clear that a massive extraterrestrial body caused the 200-kilometre-wide Chicxulub crater and wiped out 75% of life on Earth, the meteorite’s precise classification remained uncertain. Previous evidence suggested a carbonaceous chondrite, but this group includes a wide variety of meteorites, making it difficult to narrow down the specifics.
The new research, led by an international team from the University of British Columbia, the Institut de Physique du Globe de Paris, and universities in Brussels and Vienna, focused on the isotopic 'fingerprint' left behind in the global iridium-rich clay layer formed by the impact. By measuring nickel isotopes with unprecedented precision, the team matched the chemical signature to CO chondrites—a subgroup so rare that they make up only a small percentage of all meteorites found on Earth.
CO chondrites, also known as Ornans-type carbonaceous chondrites, are among the most primitive and unaltered materials in the Solar System. The study’s findings suggest that the Chicxulub impactor originated from a remote and icy region, possibly at the edge of the outer asteroid belt or even further, near Jupiter. This means the object that changed the course of life on Earth was not only massive but also exceptionally uncommon.
The research also challenges earlier theories about the aftermath of the impact. While it was previously thought that sulfur from the meteorite itself contributed significantly to the global climate catastrophe, the new data indicate that CO chondrites contain far fewer volatile elements like sulfur, carbon, and water than other types. As a result, the catastrophic darkness and cooling that followed the impact were likely caused mainly by fine dust from the pulverized Earth’s crust, rather than from the meteorite’s own composition.
Identifying the meteorite’s type required overcoming major technical hurdles. Only a minuscule fraction of the original object survived in the iridium-rich clay layer, as most of it vaporized on impact. The precise isotopic analysis acted as a 'barcode', allowing researchers to trace the meteorite’s origin despite the destruction.
This discovery not only clarifies the nature of the Chicxulub impactor but also highlights the extraordinary circumstances that led to the extinction event. Being struck by such a rare and distant object underscores the element of chance in Earth’s history. The extinction of the dinosaurs, which dominated the planet for over 160 million years, paved the way for mammals—and eventually humans—to thrive.
For context, CO chondrites represent less than 5% of all carbonaceous chondrites, which themselves make up only a small portion of meteorites found on Earth. The vast majority are ordinary chondrites. The identification of the Chicxulub impactor as a CO chondrite provides new insight into the diversity of objects that cross Earth’s path and the unpredictable nature of planetary events. This research may prompt further studies into the origins and trajectories of rare meteorites, as well as their potential impact on Earth’s future.
