Chicxulub: the end of the dinosaurs
The impact that ended the age of the dinosaurs.
Key facts
- When
- 66 million years ago
- Where
- Yucatán Peninsula and Gulf of Mexico, Mexico
- What hit
- an asteroid about 10 km across, travelling at about 20 km/s
- Era
- Deep time
- Location
- 21.30° N, 89.50° W
About 100 million megatons of TNT (roughly 4 × 10²³ joules), though estimates range from a few tens to a few hundreds of millions.
Billions of times the Hiroshima bomb, and tens of thousands of times all the nuclear weapons on Earth set off together.
What happened
Sixty-six million years ago an asteroid about 10 km wide struck a shallow sea at the edge of what is now the Yucatán Peninsula in Mexico. It blasted out a crater about 180 to 200 km across, now buried under younger rock.
In 1980 the physicist Luis Alvarez and his son, the geologist Walter Alvarez, with colleagues, reported a thin clay layer at the boundary between the Cretaceous and Palaeogene periods that was rich in iridium, a metal rare in Earth's crust but common in meteorites. They proposed that a giant impact had caused the mass extinction. The crater itself was recognised in 1990 and 1991 from old oil-exploration data, drill cores and gravity maps.
The asteroid's chemistry, read from traces in the boundary layer, points to a carbonaceous chondrite: a dark, carbon-rich rock from the outer asteroid belt.
Effects
The blast sent huge tsunamis across the Gulf of Mexico and beyond, set off earthquakes, and threw molten rock into space, which rained back down around the world as glowing beads. The target rock was rich in sulphur-bearing minerals, and the sulphur, soot and dust lofted into the upper atmosphere dimmed sunlight and caused years of cold, an impact winter that stopped plants growing and collapsed food chains. About three-quarters of all species died out, including all dinosaurs except birds, the great marine reptiles and the ammonites. Massive volcanic eruptions in India, the Deccan Traps, were happening at the same time, and how much they added is still being studied.
The evidence
The iridium-rich boundary layer found worldwide, with shocked quartz and spherules; tsunami deposits around the Gulf; the buried crater itself, mapped by geophysics and drilled in 2016 into its ring of mountains, called the peak ring; and dating that places crater and extinction at the same moment to within a few tens of thousands of years.
Did you know?
Growth rings in the bones of fossil fish killed within an hour of the impact, at a site in North Dakota, suggest it happened in the northern hemisphere's spring.
Within a few years of the impact, life was returning to the crater itself: fossil burrows and microbes appear in the rock that filled it.
Related pages
How is impact energy measured? See energy explained, or try the impact calculator.