The Chicxulub impact event, approximately 66 million years ago, was a pivotal moment in Earth’s history. An asteroid, 10 to 15 kilometers in diameter, struck the planet, forming a massive crater off the coast of what is now Mexico’s Yucatán Peninsula. This collision is widely accepted as the primary cause of the Cretaceous-Paleogene extinction event, leading to the demise of approximately 75% of all plant and animal species, including non-avian dinosaurs. The immense scale of this event significantly reshaped life on the planet.
Why It Isn’t Visible
The Chicxulub crater is not visible from Earth’s surface, unlike more recent, smaller impact craters. A significant portion of the crater lies offshore, buried beneath the waters of the Gulf of Mexico, with the rest extending inland under the Yucatán Peninsula. Over millions of years, natural geological processes have concealed this massive structure. The crater is covered by hundreds of meters to one kilometer of marine and continental sediments accumulated since the impact. Its vast size, estimated at 180 to 200 kilometers in diameter, also makes it difficult to perceive as a distinct geological feature from ground level.
How We Know It’s There
The discovery and mapping of the Chicxulub crater relied on specialized scientific techniques, rather than direct visual observation. In the late 1970s, geophysicists Antonio Camargo and Glen Penfield, working for a Mexican oil company, identified an unusual circular pattern in their subsurface data while searching for petroleum. This pattern became key to unlocking the crater’s secrets.
Scientists utilized gravity anomaly mapping, which detects subtle variations in Earth’s gravitational field caused by differences in rock density beneath the surface. These surveys revealed a distinct “bullseye” pattern, indicating a large, buried circular structure with lower-than-normal gravity values in some areas, suggesting fracturing and structural disturbances. Airborne magnetic surveys identified a nearly perfect circular anomaly roughly 180 kilometers in diameter. Seismic surveys, which use sound waves to create detailed images of subsurface geological layers, confirmed the multi-ringed structure of the hidden crater. These geophysical methods collectively allowed researchers to infer the presence, size, and shape of the concealed impact site.
Physical Evidence and Exploration
Beyond geophysical data, physical evidence from drilling provides tangible proof of the Chicxulub crater’s existence. Initial petroleum boreholes yielded clues, but later scientific drilling provided definitive evidence. Core samples from within and around the crater reveal unique materials formed during an asteroid impact.
One such indicator is shocked quartz, a form of quartz with microscopic structural deformations that can only occur under immense pressure from a hypervelocity impact. Core samples also contain impact melt rocks, solidified materials formed from target rocks instantly vaporized and melted by the asteroid’s energy. Small glass spherules, known as tektites and microkrystites, ejected during the impact, represent solidified molten rock found at the Cretaceous-Paleogene boundary layer worldwide. Recent scientific drilling expeditions, including those by the International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) in 2016, recovered continuous core samples from the crater’s peak ring, offering insights into its formation and the recovery of life after the impact.