Evidence from locations across the globe supports the idea that a large asteroid struck Earth near the present-day Gulf of Mexico at the end of the Cretaceous Period. This animation shows the globe at the end of the Cretaceous, when dinosaurs still roamed among recently evolved flowering plants.

Scientists theorize that huge amounts of water and dust entered the atmosphere and blocked sunlight for years, cutting the energy supply of plants on land and in the ocean. Without sunlight, the base of the food chain was devastated. Over half of the plant and animal groups that were living during the Cretaceous Period were extinct when the Tertiary Period began.