Cretaceous-Paleogene Boundary (65 Million Years Ago)
This rendering shows life at the end of the Cretaceous Period, before the impact of a 6.2 mi (10 km) asteroid triggered mass extinctions on land and sea. Dinosaurs are the most famous victims of the extinction at the end of the Cretaceous, 65 million years ago. But they weren't alone. Nearly half of Earth's species disappeared -- including almost 75 percent of ocean species. Evidence indicates an asteroid was to blame. Dust and smoke from the impact blocked sunlight, disrupted photosynthesis and altered Earth's climate. Explore the ancient ocean in an image gallery or in our Ocean Over Time interactive.