Ian Rumbold, age 8, of Ottawa, Ontario, Canada for his question:

Why did the dinosaurs die out?

Scientists cannot give a definite answer to this question. At present, we do not know enough about the past to explain exactly why the mighty dinosaurs suddenly departed from the planet Earth. However, scientists are allowed to make guesses, so long as their guesses are sensible. But a guess, of course, is not the same thing as a definite answer. Until it can be proved right or wrong, we must call it a theory.

The dinosaurs were giant reptiles and through millions of years they were used to a warm, moist climate. Perhaps the world wide weather suddenly became too hot or too cold, too dry or too damp for them. Perhaps they were infected by sudden plagues. Perhaps their favorite foods were crowded out by grasses, which they could not eat. These ideas are just guesses, called theories. But until we learn a lot more, nobody can say for certain why the dinosaurs were wiped out.