Different people believe different theories about why dinosaurs became extinct. Some people think that their extinction was caused by a giant meteorite smashing into our planet. The meteorite would have been very large in size. When it hit the Earth, a large dust cloud would have formed covering everything on the planet for a great number of years. This would have prevented sunlight from reaching all of the Earth's plants. Since the plants would die without sunlight, the plant-eating dinosaurs (herbivores) would all die, too. Dinosaurs that ate the plant-eating dinosaurs (carnivores) would also die without their food source. No one knows whether or not a giant meteorite really hit the Earth causing the dinosaurs to become extinct, but many people believe that this theory is true.

According to this passage, what do some people believe caused dinosaurs to become extinct?