Sixty-six million years ago, a massive object slammed into what is now the Yucatán Peninsula in Mexico, throwing enough debris into the atmosphere to dim the Sun, cool the planet and kill roughly three-quarters of all species — including every non-avian dinosaur. For decades the broad cause was agreed upon, but the actual rock responsible had remained unidentified.
A new study led by researchers at the University of British Columbia, with colleagues in Paris, Brussels and Vienna, has finally named it. Published in Science Advances, the work used advanced nickel isotope analysis on samples of impact material to narrow the composition of the killer meteorite to a rare class known as CO chondrites — primitive, carbon-rich meteorites of the so-called Ornans family.
CO chondrites are unusual compared with the stony meteorites more often displayed in museum collections. They contain far less of the so-called volatile elements — carbon, zinc, water and especially sulfur — than other meteorite classes found on Earth. That distinction reshapes part of the extinction story. A leading theory had held that sulfur locked inside the impactor was a key driver of the sudden global cooling that followed the strike. If the impacter itself carried little sulfur, the smoking gun likely came from vaporised rock and sediment at the impact site rather than from the asteroid alone.
The team concluded the impacter probably formed in the outer asteroid belt between Mars and Jupiter, consistent with the chemistry of CO chondrites. The fine debris it kicked up was what spread through the atmosphere, blocking sunlight and triggering the ecological collapse that ended the age of the dinosaurs.
Knowledge takeaway: nickel isotope analysis identifies a rare CO chondrite meteorite as the probable impactor of 66 million years ago; CO chondrites are carbon-rich but sulfur-poor, suggesting the global cooling was driven more by vaporised target rock than by sulfur in the asteroid itself; the killer likely originated in the outer asteroid belt.