John Ashbrook, age 9, of Allentown, Pennsylvania, for his question:

Why is the inside of the earth so hot?

The cool crust is only about 40 miles thick. Below it, the layers get hotter and hotter as we go deeper towards the central core. Down there in the middle of the globe, it is thought that the temperature is as high as 9,000 degrees Fahrenheit. Scientists know that the center of the earth is very, very hot. But they are not absolutely certain what makes it this way. They suspect that several things may help.

Scientists agree that there are radioactive materials down inside the earth. These, as we know, give off a lot of heat and most likely they help to heat the earth's core. Pressure from heavy layers around the core also adds heat. I lost experts agree that the newborn earth was a ball of hot molten material. As the outer layer cooled, it formed a solid crust. The cool solid crust may have helped to seal some of the original heat in¬side the core. Most likely all of these things helped to make the middle of the earth hotter than hot.