The Chicxulub Impact: Evidence for the End of Non-Avian Dinosaurs

About 66 million years ago, an asteroid struck the shallow sea near what is now Mexico’s Yucatán Peninsula. The resulting Chicxulub crater is buried beneath later rocks, but evidence of the impact appears far beyond the crater itself. A worldwide boundary layer contains anomalous iridium, shocked minerals and impact spherules. Together with the crater’s age and the abrupt fossil turnover, these observations connect the collision to the Cretaceous–Paleogene, or K–Pg, extinction.

From a thin boundary layer to a buried crater

In 1980, Luis and Walter Alvarez and colleagues reported an iridium-rich layer at the boundary between Cretaceous and Paleogene rocks. Iridium is scarce in Earth’s crust but more common in many meteorites. The team proposed that a large impact had spread vaporised and pulverised material around the planet. Later work identified shocked quartz and glassy spherules in boundary sediments, adding evidence for extreme pressures and molten ejecta.

The Chicxulub structure was mapped beneath the Yucatán region using geophysical data and drilling. Core samples contain impact melt and shocked rocks. The crater’s size, its impact materials and its close age match to the boundary layer provide a physical source for the ejecta. A globally distributed iridium anomaly preserved within the crater has further linked its deposits to the same event.

What happened after the impact?

The impact released enormous energy, excavated rock and launched material into the atmosphere. Near the crater, heat, seismic shaking and ocean waves would have been severe. Farther away, the most consequential effects likely involved material and gases injected into the atmosphere. Fine dust, soot from fires and sulfur-bearing aerosols could reduce sunlight, disrupt photosynthesis and cool the surface. Their relative contributions and duration are reconstructed through sediment records and climate models rather than directly observed.

Food webs that depended on primary production were vulnerable to a sudden loss of light and changing climate. Fossil assemblages document a sharp turnover across the boundary in marine plankton and many land groups. The catastrophe was not a single instant experienced identically everywhere: local environments, seasonality and food-web structure shaped which populations endured.

Impact and volcanism in the larger extinction story

The Deccan Traps in India record massive volcanism around the same broad interval. Volcanic gases could influence climate and ecosystems before and after the impact. Researchers continue to evaluate how the timing and pace of eruptions interacted with the asteroid event. The geological case for Chicxulub is strong, while the precise share of different environmental stresses is a more detailed question.

“Meteorite” is often used casually, but before impact the object was an asteroid or other extraterrestrial body; meteorites are pieces that survive passage through an atmosphere and reach the ground. The impact model is not based on the dramatic image of a fireball alone. It rests on a chain of testable evidence: crater structure, shock effects, geochemical anomalies, ejecta deposits and coincident biological change.

Extinction was selective

All non-avian dinosaurs disappeared, but birds survived as the one living dinosaur lineage. Crocodilians, turtles, mammals and several other groups also crossed the boundary, though many species were lost. Survival depended on ecology, body size, habitat and food supply; no single trait explains every outcome.

The event closed the Mesozoic Era and reshaped ecosystems, but it did not erase all life. The fossil record after the boundary shows survivors diversifying into altered environments. See how birds crossed the K–Pg boundary and the wider comparison of impact, volcanism and extinction evidence.