A timeline in stone
In 2016, a scientific drilling platform named L/B Myrtle positioned itself in the Gulf of Mexico, about 20 kilometers northwest of Progreso, Mexico. Its mission, IODP-ICDP Expedition 364, was to drill into the submerged peak ring of the Chicxulub impact crater. The drill bored through 505 meters of younger ocean sediments before reaching the 66-million-year-old rock deposited in the first minutes and days after a 10-kilometer-wide asteroid struck the Earth. The final core sample reached a depth of 1,334.7 meters below the seafloor.
This cylindrical column of rock provides a high-resolution timeline of the event that ended the Cretaceous period. The impact itself bored a hole nearly 160 kilometers wide in seconds. The energy released was equivalent to 10 billion of the atomic bombs used in World War II. The drill core shows what happened next. Deep granite from the Earth's crust, normally found kilometers down, was liquefied, shot to the surface, and collapsed outward to form the mountainous peak ring in under 90 seconds. The core contains this shocked granite, which is fractured and crosscut with veins from the intense pressures. Above this lies a thick layer of impact melt rock and suevite, a chaotic breccia of melted rock, glass, and shattered mineral fragments from the target rock and the asteroid itself.
Evidence of a global catastrophe
The first 130 meters of rock above the peak ring were deposited within a single 24-hour period. The layers chronicle an almost unimaginable sequence of events. After the initial formation, the crater was covered by about 80 meters of melted stone and rock fragments from the collapsing plume of vaporized rock. Then, a massive tsunami, possibly over a kilometer high, surged back into the hot crater. This wave carried with it a jumble of gravel, sand, and charcoal from continent-spanning wildfires ignited by the impact. The presence of this charcoal within the core is evidence of the global firestorm.
One of the most important discoveries within the core came from a thin layer just above the chaotic impact deposits. Here, scientists from four independent labs confirmed the presence of an iridium anomaly. Iridium is rare in Earth's crust but common in asteroids. This specific layer, containing extraterrestrial dust, is the same "golden spike" found in the K-Pg boundary layer at over 350 sites worldwide. Its preservation inside the crater links the Chicxulub impact to the global mass extinction event that wiped out approximately 75% of all species, including the non-avian dinosaurs. The absence of sulfur-rich rocks, which should be present, also supports the theory that the vaporized sulfur from the impact site created a global haze that blocked sunlight and drastically cooled the planet.