About 66 million years ago, an asteroid roughly 10 kilometres wide struck what is now Mexico’s Yucatán Peninsula. It excavated the Chicxulub crater, sent material around the planet and coincided with the extinction of about three quarters of species, including every non-avian dinosaur.
Size is the obvious part of this story. A rock that large arriving at planetary speed is difficult to think about in ordinary terms. But the more revealing detail is what it hit.
Chicxulub lay beneath a shallow sea over carbonate and sulphate-rich rocks. The collision did not merely throw asteroid dust into the air. It heated, melted and vaporised part of the target itself, launching sulphur-bearing gases, fine rock dust and other material into the atmosphere. The place beneath the asteroid helped determine what happened far beyond the crater.
The crater is only the beginning
For life close to the impact, the first effects were direct: shock waves, intense heat, earthquakes, ejecta and enormous water movement around the Gulf of Mexico. Yet those effects alone do not explain a mass extinction recorded in rocks around the world.
The global mechanism involved the atmosphere. Sulphate aerosols and fine dust can reduce the sunlight reaching Earth’s surface. Cooling follows, photosynthesis slows and food webs lose the primary production on which larger organisms depend.
A 2019 study in the Proceedings of the National Academy of Sciences examined cores drilled from Chicxulub’s peak ring. The researchers described about 130 metres of impact melt rock and broken debris deposited during the first day of the Cenozoic era. They found charcoal, evidence consistent with fires, but a striking shortage of the sulphur-rich rocks that had originally occupied the site.
Their interpretation was that much of that sulphur-bearing material had been vaporised and ejected rather than simply mixed into the crater deposit. Once in the atmosphere, sulphur could form sunlight-reflecting aerosols.
The angle made the target matter more
The impact was not straight down. A 2020 Nature Communications study used three-dimensional simulations of crater formation to compare possible trajectories with the buried structure measured at Chicxulub. The authors concluded that the asteroid most likely arrived from the north-east at an angle of roughly 45 to 60 degrees from the horizontal.
In the team’s models, that steeply inclined path was efficient at vaporising sedimentary target rocks and ejecting climate-active gases at high speed. An extremely shallow or near-vertical impact would have coupled with the target differently.
This is modelling constrained by crater observations, not a camera recording of the impact. The exact amount and balance of dust, soot, sulphur and carbon-bearing gases remain active research questions. Still, the geometry helps explain why “a 10-kilometre asteroid” is not a complete description of the event. Diameter tells us about the object. It does not tell us how energy moved through a particular stack of rock.
Sulphur mattered, but the number is still being revised
It is tempting to tell the extinction as one clean chain: sulphur entered the atmosphere, the planet cooled and the dinosaurs died. The evidence supports an abrupt impact-driven environmental crisis, but the proportions inside that chain are less tidy.
A 2024 study of sulphur in Cretaceous-Palaeogene boundary sediments estimated that the impact released substantially less sulphur than several earlier models assumed. The authors did not argue that sulphur was irrelevant. They argued that silicate dust and soot may need to carry more of the explanation for the cooling than older high-sulphur scenarios allowed.
I find this uncertainty useful rather than disappointing. The broad event is well supported, while its atmospheric recipe is still being refined as researchers obtain better cores, isotope measurements and climate models. Science can become more precise without reversing the central account.
The asteroid had a history, and the ground supplied an aftermath
I recently wrote about evidence that traced the Chicxulub impactor’s material to beyond Jupiter. That work asks where the object came from. The target-rock research asks a different question: what did Earth add to the collision?
Both sides matter. An asteroid brought the energy, but the Yucatán platform supplied material that could travel through the atmosphere and change conditions across the planet. Extinction was not simply the footprint of a large rock. It was the result of that rock meeting this world at one specific place and angle.
That distinction also adds context to modern deflection research. When I looked at China’s proposed kinetic-impact asteroid test, the engineering question was how a spacecraft might alter a small object’s motion. Chicxulub shows why even a modest change in an impactor’s path could matter over planetary distances. Destination is part of consequence.
The dinosaurs were not destroyed because one asteroid possessed a special kind of evil. They were caught in a physical sequence involving speed, angle, water, rock and atmosphere. The asteroid was enormous. The geology beneath it made the damage global.
