The meteorite that struck the Yucatán Peninsula about 66 million years ago and triggered the extinction of the dinosaurs was one of the rarer types in the Solar System. A study published in Science Advances used nickel-isotope analysis to identify the Chicxulub impactor as a CO chondrite, a class found in only a small fraction of known meteorite samples.
The impact formed the Chicxulub crater, roughly 200 kilometres wide, at the Cretaceous-Paleogene boundary, when about 75% of life on Earth disappeared. Scientists have long studied material left by the collision to understand the impactor and its effects on the planet. Iridium is a particularly useful tracer: extraterrestrial material can contain concentrations up to 100,000 times higher than ordinary terrestrial rocks.
An international team from the University of British Columbia and the Institut de Physique du Globe de Paris, alongside university teams in Brussels and Vienna, examined the isotopic fingerprint preserved in the globally distributed iridium-rich clay layer. The paper, titled “Globally distributed iridium layer preserved within the Chicxulub impact structure,” focuses on identifying the impact marker inside the crater and in boundary deposits found around the world.
Pinpointing the layer presented a technical challenge. Chicxulub’s impact-related deposits are hundreds of metres thick, but the diagnostic clay layer is only centimetres thick. Researchers at Lund University used a specialized iridium spectrometer to locate and analyze the narrow horizon in drill cores containing crushed rock and redeposited sediment from inside the impact structure. Nickel-isotope analysis matched the chemical signature to CO chondrites, a subgroup that makes up only a small share of meteorites found on Earth.
Also known as Ornans-type carbonaceous chondrites, CO chondrites are among the Solar System’s most primitive materials. The findings suggest that the Chicxulub impactor came from a remote region, possibly near the outer asteroid belt or farther out, near Jupiter. CO chondrites account for less than 5% of carbonaceous chondrites; most meteorites found on Earth are ordinary chondrites.
The findings also add context to the environmental aftermath. The evidence points to an initial cooling phase, as dust and ejecta blocked sunlight, followed by extreme greenhouse conditions as impact gases remained in the atmosphere. Birger Schmitz, a researcher at Lund University, said the record shows that Earth first cooled under the dust, then experienced an extreme greenhouse climate after the impact gases remained in the atmosphere. His Lund colleagues Per Kristiansson and Mikael Elfman also worked on the research into the crater deposits.
The new data indicate that CO chondrites contain fewer volatile elements, including sulfur and carbon, with less water than some other meteorite types. That finding bears on explanations of the climate catastrophe: fine dust from pulverized terrestrial rock likely drove the immediate darkness and cooling, while impact-derived gases contributed to later warming.
Only a tiny fraction of the impactor’s material survived in the iridium-rich layer; most of the object vaporized on impact. Nickel-isotope analysis works as a chemical fingerprint, allowing researchers to identify the meteorite’s type from the small amount of extraterrestrial material preserved in the geological record.
The discovery sharpens the picture of the object linked to the extinction event and the environmental changes that followed. Dinosaurs dominated the planet for more than 160 million years; their extinction opened ecological space for mammals, eventually including humans. Identifying the impactor as a rare CO chondrite also gives researchers a new point of reference for studying the origins and trajectories of meteorites that cross Earth’s path.
