The crater is almost invisible from the ground. It lies beneath younger limestone and seafloor sediment at the northern edge of Mexico’s Yucatán Peninsula, with roughly half of the structure under land and half beneath the Gulf of Mexico. Yet this buried circle records one of the most consequential moments in Earth’s history: an asteroid impact 66 million years ago that brought the Cretaceous Period to an abrupt end.
Chicxulub was not merely an explosion on a continental scale. The collision disturbed the atmosphere, oceans, and food webs in rapid succession. About three-quarters of species disappeared in the resulting Cretaceous–Paleogene, or K–Pg, mass extinction. Non-avian dinosaurs were among the losses, while birds—the only surviving dinosaur lineage—passed through the crisis alongside mammals, crocodilians, turtles, and other groups whose survival reshaped later ecosystems.
A Buried Basin About 180 Kilometers Wide
The impactor was probably an asteroid about 10 to 12 kilometers across. It struck a shallow tropical sea over carbonate and sulfate-rich rocks at enormous speed, releasing energy far beyond any human-made explosion. The first cavity was unstable: rock was compressed, excavated, melted, and displaced within minutes. Its walls collapsed inward while deeply buried crust rebounded upward, then fell outward to form a circular peak ring.
The final basin measured about 180 kilometers across. Several hundred meters to roughly a kilometer of later sediment now cover it, so Chicxulub lacks the open bowl associated with a young crater. Geophysical surveys reveal its concentric structure underground. At the surface, a curved belt of cenotes traces part of the buried rim, where groundwater was redirected through fractured limestone and enlarged sinkholes over time.
The Crater Was Found After the Extinction Clue
Scientists first recognized evidence of the catastrophe far from Mexico. A thin boundary layer marking the end of the Cretaceous contains unusually abundant iridium, an element scarce in Earth’s crust but relatively common in asteroids. Researchers also found glassy droplets produced from airborne melt and quartz grains scarred by pressures that ordinary volcanic or tectonic activity cannot generate.
Meanwhile, petroleum surveys in the Yucatán had mapped a large circular gravity and magnetic anomaly. Geophysicists Glen Penfield and Antonio Camargo recognized the buried form in data assembled during the late 1970s, but its importance was not immediately established. The search accelerated after unusually thick impact deposits in Haiti pointed toward the Gulf of Mexico. Reexamined drill core from the Yucatán then yielded impact melt, breccia, and shocked minerals. By the early 1990s, the buried structure and the worldwide boundary layer had been tied to the same event.
That connection rests on several converging lines of evidence rather than resemblance alone. The crater and boundary deposits have matching ages. Ejecta become thinner with distance from the Yucatán, while the sizes of shocked grains also decrease outward. Melt material in distant deposits is chemically compatible with rock from the crater. Together, these patterns locate Chicxulub as the source of the debris spread around the planet.
Minutes of Destruction Around the Gulf
Near the impact site, survival would have been nearly impossible. A radiant fireball, an extreme pressure wave, high-velocity winds, falling ejecta, and intense seismic shaking devastated the Gulf region. Because the asteroid struck shallow water, it also drove immense tsunamis. Disturbed sediment and tsunami deposits occur around the Gulf of Mexico and beyond, preserving evidence of water moving violently across coasts and seafloors.
These immediate effects were devastating but geographically limited. The extinction became global because vaporized target rock and impact debris entered the atmosphere. Molten droplets and fragments traveled on ballistic paths before falling back, and fine particles remained aloft much longer. The composition of the Yucatán target proved especially damaging: vaporized sulfate-bearing minerals supplied sulfur that could form sunlight-reflecting sulfate aerosols.
An Impact Winter Broke Food Webs
Dust, sulfate aerosols, and soot sharply reduced the sunlight reaching Earth’s surface. Temperatures fell, and photosynthesis slowed or stopped across many environments. That failure struck the foundation of food webs. On land, plant loss deprived herbivores of food and then affected predators. In the oceans, the decline of photosynthetic plankton disrupted ecosystems from the bottom upward.
Other stresses overlapped with the darkness and cooling. Heated atmospheric gases contributed to acid rain, while reentering debris and regional fires added smoke and chemical disruption. The exact distribution of wildfires remains debated, and different particles stayed airborne for different lengths of time. The central mechanism, however, is clear: the collision converted rock into a planet-circling atmospheric burden faster than most organisms could adapt.
Large eruptions in India’s Deccan Traps were also changing climate around the K–Pg boundary. Their role remains important to understanding conditions before and after the extinction. The sharp coincidence of Chicxulub ejecta with the biological turnover, however, identifies the impact as the decisive trigger of the mass extinction. Volcanism may have added background stress, but it does not replace the crater-centered evidence.
A Geological Boundary With a Biological Meaning
Chicxulub ended a period, not life itself. Survival varied with habitat, body size, diet, geography, and the ability to endure disrupted food supplies. Organisms that could shelter, eat detritus, or use freshwater food chains sometimes had advantages. The survivors inherited ecosystems emptied of many dominant groups, opening ecological opportunities that shaped the early Paleogene.
The crater therefore connects a brief physical event with a long biological transformation. Its rocks record shock, melting, collapse, and later hydrothermal circulation; the global boundary layer records what escaped the basin. Read together, they show how a collision lasting minutes ended the Cretaceous and redirected life for millions of years.