Dinosaurs went extinct 65 million years ago for reasons that are still unknown, but we still have theories. So in conclusion, we know that the impact theory shows that a meteorite or asteroid hit the earth kicking up enough dust to block the sun affecting the food chain. Affecting the dinosaurs. The dinosaur-killing crash threw huge amounts of debris into the air and caused massive tidal waves to wash over parts of the American continents. There is also evidence of substantial fires from that point in history. A new theory says the dinosaurs were killed by a comet fragment that originally came from the solar system's edge. For decades, the prevailing theory about the extinction of the dinosaurs was that an asteroid from the belt between Mars and Jupiter slammed into the planet, causing cataclysmic devastation that wiped out most life on the planet.