Why did dinosaurs become extinct?

Dinosaurs existed on Earth 65 million years ago. Today, the scientists believe that their mass extinction was triggered by a huge meteorite hit to the east of Mexico. The meteorite impact caused blasts and flood waves. Huge quantities of poisonous gases filled the Earth's atmosphere. Then there was acid rain that polluted the seas and the plants died. Huge dust clouds blocked the heat from the sun and it became cold. The cold-blooded dinosaurs became sluggish and starved. Young ones did not hatch from their eggs. Only the small animals, which adapted themselves quickly and did not need a lot of food, survived.