The Cretaceous-Tertiary extinction was a mass exticntion that happened 65 million years ago. It was the second largest (the largest was the Permian-Triassic Extinction) extinction in the history of Earth, and probably the most famous.
The extinction began when a 6 mile (10 kilometer) asteroid slammed into the ocean approximately 100 miles (165 kliometers) of the coast of the Yucatan Peninsula in Mexico. It was a truly tremendous explosion; equal to 183 trillion tons of TNT! The fireball created was perhaps 100 miles (165 kilometers) across! Everthing nearby was vaporized instantly. The explosion produced a flaming wall of ash and embers racing across the land at hypersonic speed. Plants and animals within a thousand miles would have been obliterated. Then came a huge shockwave, continuing the destrution. Even after all this settled down, it was only the begining. Gigantic earthquakes hundreds of times stronger than the worst we have seen devestate North America. And where there are earthquakes and oceans, there are tsunamis. Massive waves crash inland, destroying sea and land life alike. Forests and swamps become seas. Also, tons and tons of dust and rocks shoot into the atmosphere and speads across the globe. Some of it falls back, starting fires and killing wildlife, but most stays up. With dust dust blocking the sun, the Earth becomes bitterly cold.