Nickel isotopes point to a rare CO chondrite as the dinosaur-killing impactor
Researchers report that nickel-isotope measurements from the global Cretaceous-Paleogene clay layer point to a rare CO carbonaceous chondrite as the asteroid that struck Earth 66 million years ago. The study, published in Science Advances, suggests the impactor itself contained relatively little sulfur, making fine debris ejected into the atmosphere a more likely primary driver of cooling than sulfur from the meteorite. The object’s original source remains uncertain.
The story
A research team involving scientists at the University of British Columbia and institutions in Paris, Brussels and Vienna has reported evidence identifying the object behind the Cretaceous-Paleogene impact as a CO chondrite, a rare type of carbonaceous meteorite. The researchers measured nickel isotopes in material from the thin clay layer deposited globally after the impact 66 million years ago. According to the report, that isotope signature enabled them to distinguish the impactor’s likely meteorite class even though only a minute fraction of the original projectile remains in the layer. The impactor is estimated to have been 10 to 15 kilometers across and to have struck at roughly 64,000 km/h. It formed the Chicxulub crater, now buried under Mexico’s Yucatán Peninsula, and is linked in the report to an extinction affecting about 75% of species, including all non-avian dinosaurs. The findings were published in Science Advances. The proposed CO-chondrite identity does not change the conclusion that an impact caused the extinction event. It does, however, alter the composition-based explanation under consideration. Because CO chondrites contain relatively little sulfur, the researchers say sulfur delivered inside the asteroid is less likely to have been the central cause of the subsequent global crisis. They instead point to the enormous amount of fine debris injected into the atmosphere as the likely primary factor.
Why it matters
The main consequence is a more constrained account of the mechanism following the Chicxulub collision. Earlier explanations can emphasize sulfur released by an impactor or by affected rocks; this result specifically reduces the case for sulfur contained in the incoming object because CO chondrites are sulfur-poor. That directs future geochemical and climate-focused work toward testing the role of fine particulate debris lofted by the collision. It also shows that globally distributed boundary sediments can retain enough chemical information to identify an object that no longer exists as an intact sample.
Evidence and context
The Cretaceous-Paleogene impact is associated with a global clay layer that preserves traces of the object despite the projectile having vaporized. The reported analysis draws on samples collected over many years from that layer, rather than on a surviving meteorite fragment. Carbonaceous chondrites make up about 5% of meteorites sampled on Earth, and CO chondrites are a small subset of them. The source describes them as primitive, relatively unaltered material from the Solar System’s formation, so classifying the impactor can inform both impact research and models of where its precursor originated.
Limits and unknowns
The identification is a likelihood, not a recovered piece of the impactor. Researchers are working from minute traces in the K–Pg clay layer because the meteorite vaporized on impact, which limits the material available for comparison. Its original source also remains unresolved: the report says it may have come from a distant outer-Solar-System debris region or the outer asteroid belt near Jupiter. The evidence therefore narrows the impactor’s class but does not establish a unique birthplace or fully settle which atmospheric materials drove the extinction.
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Story timeline
Chicxulub impact
An estimated 10- to 15-kilometer-wide impactor struck Earth, forming the Chicxulub crater beneath what is now Mexico’s Yucatán Peninsula.
Study reported
ScienceDaily published the University of British Columbia account of the nickel-isotope study.
Nickel isotopes point to a rare CO chondrite as the dinosaur-killing impactor
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Highlights
- Nickel isotopes reveal meteorite type
- Chicxulub crater formed by impact
- Low sulfur content in impactor
- New insights guide climate studies
Transcript
Scientists traced nickel isotopes in global clay to a rare CO carbonaceous chondrite impactor.
This asteroid struck Earth 66 million years ago, creating the Chicxulub crater in Mexico.
CO chondrites contain little sulfur, shifting focus to fine debris as the main cooling cause.
The study narrows impact mechanisms, guiding future climate research on atmospheric particles.
Global sediments preserve chemical clues, helping identify vanished meteorites and their effects.