Chicxulub
Key facts
- Country
- Mexico
- Diameter
- 180 km
- Age
- about 66 million years
- Location
- 21.33° N, 89.50° W
Nothing obvious at the surface: the crater is buried under about a kilometre of younger limestone. Its outline is traced by a curved ring of cenotes (water-filled sinkholes) across the Yucatán Peninsula.
Chicxulub is the crater that ended the age of the dinosaurs. About 66 million years ago an asteroid roughly 10 km across struck the shallow sea covering what is now the Yucatán Peninsula in Mexico. The crater it left is about 180 km wide, and the disaster that followed wiped out around three quarters of all plant and animal species on Earth, including all non-bird dinosaurs.
Clues from a thin layer. The story began not in Mexico but in Italy. In 1980 the physicist Luis Alvarez, his geologist son Walter Alvarez and colleagues reported that a thin layer of clay marking the boundary between the Cretaceous and Palaeogene periods (the K–Pg boundary) was unusually rich in iridium, a metal rare in the Earth's crust but common in many meteorites. They proposed that a huge impact had spread this iridium worldwide. The same layer was soon found around the globe, along with shocked quartz, tiny glass spherules and soot from fires.
Finding the crater. The missing piece was the crater itself. Geophysicists Glen Penfield and Antonio Camargo, working for the Mexican oil company Pemex, had noticed a huge circular structure in gravity and magnetic data in the late 1970s and presented it in 1981, but the find attracted little attention at first. In 1991 Alan Hildebrand and colleagues linked it to the K–Pg layer, naming it after the village of Chicxulub near its centre. Rock samples from old oil wells showed shocked minerals and impact melt, and dating gave an age matching the extinction.
Inside the crater. Chicxulub is a peak-ring crater: inside the outer rim lies a ring of mountains formed when the central uplift collapsed outwards within minutes of the impact. In 2016 an international drilling expedition drilled into the peak ring from a platform offshore and recovered granite that had been lifted from deep in the crust and intensely shocked. The cores showed how quickly life began to return to the crater after the disaster.
What happened next. The impact vaporised rock rich in sulphur and carbon, throwing dust and sulphate aerosols high into the atmosphere. Sunlight was dimmed for months to years, temperatures fell sharply and photosynthesis faltered, collapsing food chains. Huge tsunamis swept the Gulf of Mexico, and wildfires may have burned across large areas. Debate continues over how much the volcanic eruptions of the Deccan Traps in India, which were happening around the same time, added to the crisis, but the impact is widely accepted as the main trigger.
Seeing it today. There is no rim to stand on. The crater is buried under younger limestone, and the only surface hint is the Ring of Cenotes, a curved line of sinkholes that follows fractures above the buried rim. Many cenotes are popular swimming spots. Museums in and near Mérida tell the crater's story.
Did you know?
The crater was first spotted by oil company geophysicists, not by scientists searching for it.
Without the Chicxulub impact, mammals might never have risen to dominate the land.
Tiny glass beads made by the impact rained down as far away as North Dakota.