Cretaceous-Paleogene Boundary

The Cretaceous-Paleogene (K-Pg) Boundary is a geological marker marking the transition between the Cretaceous and Paleogene periods, about 66 million years ago. It is most famous for a massive extinction event that wiped out about 75% of Earth's species, including the dinosaurs. This boundary is characterized by a thin layer of clay rich in iridium, a rare metal often associated with asteroids. Most scientists believe a large asteroid impact caused a chain of environmental changes—such as global fires, tsunamis, and climate shifts—that led to the mass extinctions.