It still remains a scientific puzzle. One opinion is that the earth’s climate grew cooler and the forest dwindled. With the loss of their habitats they died out. Another answer may lie in outer space. Had the earth been hit by a commet or huge meteorite there would have been great explosion. Dust rising into the atmosphere would have blotted out the sun’s warmth. The plants on which the dinosaurs fed would have died out and so would they.
