The Earth was fairly warm during the period preceding 65 million years ago, which is why the cold-blooded reptiles could survive. Vegetation was lush. About 65 million years ago, it is believed that a major meteorite strike occurred on Earth, which sent up gigatons of dust and smoke from burning vegetation into the atmosphere. The dust and smoke blocked the sunlight from reaching and warming the ground, so a rapid cooling of the global atmosphere occurred (the meteorite or comet was pretty large and the explosion from the impact was phenomenal). The dinos could not survive at these cold temperatures, so most of them died off. Warm-blooded mammals had the best survival rate. This event constituted yet another major global air pollution event, with the dust and smoke as the pollutants.