The day the earth shook
Sixty-six million years ago, a 10-kilometer wide asteroid traveling up to 150,000 miles per hour struck the shallow sea covering what is now the Yucatán Peninsula. The impact created the 200-kilometer wide Chicxulub crater and released energy equivalent to more than a billion nuclear bombs. This event triggered a magnitude 11 earthquake, blasting 400 cubic miles of debris into the atmosphere and generating a mega-tsunami.
The Brazos River area, then a sea floor about 75 to 100 meters deep, was approximately 1,000 kilometers from the impact site. The initial waves from the impact may have been over 100 meters high, scouring the Gulf of Mexico. These waves and their powerful backwash ripped up the sea floor, mixing sand, mud, boulders, and marine life into a chaotic slurry. The resulting deposit, a sandstone complex several feet thick, sits within layers of fine mudstone that had accumulated quietly for millennia. This jumbled layer of rock, exposed by erosion along the Brazos River in Falls County, records of the hours and days following the impact that ended the Cretaceous Period.
A catastrophic signature in stone
The evidence for this ancient catastrophe is unmistakable in the local geology. The event deposit contains several important markers that link it directly to the Chicxulub impact. One is the presence of shocked quartz, a type of quartz grain with a microscopic structure deformed by the immense pressure of a high-velocity impact. This feature is only known to be created by extraterrestrial impacts or nuclear explosions.
The rocks also contain tektites, small glassy beads formed from rock that was melted by the impact, blasted into the atmosphere, and rained back down. Another critical piece of evidence is a clay layer enriched with iridium, an element rare on Earth's surface but common in asteroids. The global presence of this iridium layer is one of the foundational pieces of evidence for the impact theory of dinosaur extinction. Fossils within the deposit tell a story of chaos; Cretaceous ammonites and other sea creatures are found mixed together, ripped from their habitats by the tsunami's force.