Dinosaur-Killing Asteroid (Chicxulub)
In 1980 Luis and Walter Alvarez found an iridium-rich clay layer at the end of the Cretaceous and argued that an asteroid impact killed the dinosaurs; the Chicxulub crater, tied to it in 1991, confirmed the idea.
Open in the interactive tree →Luis Alvarez, Walter Alvarez, Frank Asaro and Helen Michel reported in 1980 that clay at the Cretaceous-Paleogene boundary held 20 to 160 times the normal iridium, a metal common in asteroids and rare in Earth's crust. Geophysicists Penfield and Camargo had found a circular structure under the Yucatan in the late 1970s, and Hildebrand's group identified it as an impact crater in 1991. The impactor was about 10 km wide and the crater roughly 180 km across; the impact is dated to 66.04 million years ago, a 41-scientist review endorsed it as the cause in 2010, and drilling into the peak ring in 2016 reached 1,335 m below the sea floor. About 75% of plant and animal species died out.
Prerequisites
- Stratigraphy (Steno's Rock Layers)1669The iridium sat in a thin clay layer that marks the boundary between two rock ages.
- Nuclear Physics1938Nuclear analysis methods measured trace amounts of iridium in the clay.
Unlocks
- Planetary DefenseopenChicxulub shows what a 10 km impactor does, the threat planetary defence guards against.