Calvin Pert, age 11, of Nashwaaksis, New Brunswick, Canada, for his question:

Whv doesn't the center of the earth cool off?

Scientists cannot prove all the details, but they know for a fact that our planet is hot and still hotter below the surface. Several theories have been suggested to explain this. We know that pressure and friction create heat. The earth's core is under enormous pressures from the layers above it. The restless motions of crustal slabs generate friction dust below the surface and nobody knows precisely what motions go on in the deeper levels.     

Pressure and friction account for some of the heat sealed within the earth. But a lot more must be generated by radioactive substances, buried since the earth was formed. Tremendous heat remains sealed below    but some escapes. Some erupts in fiery volcanoes. Some may be used as energy to drive the shifting crustal plates. But at this time we cannot describe the activities of the earth's internal heat in precise detail.