Shawn Remillard, age 11, of Visalia, California, for his question:

Is it possible to melt rocks?

Yes this is possible. In fact, rock melting goes on all the time. People do a lot of it. The earth does even more and some even happens in the air above our heads. And astronomers suspect that a little rock melting ruined the tail of the comet Kohoutek. It is thought that the heat of the sun coated the comet with molten material that prevented streams of gaseous particles from escaping.

Naturally, the earth's rocks do not melt at everyday temperatures, not even in the torrid tropics. This is because the earth's surface is cool enough to freeze them solid. At high temperatures, the rocky minerals melt and become thick molten fluids, hotter than hot. At still higher temperatures, they may turn to fumes and steamy gases.

We are told that our entire world is built from about 100 chemical elements. The basic atoms of each element are all alike. In the earth's crust, gold and a few other elements occur in almost pure nuggets and nodules. Chemical compounds are made of molecules that are packages of assorted atoms. Almost all of the earth's rocky crust is made up of about 1,500 different mineral compounds. The average rock sample is a mixture of several mineral compounds.

Each rocky mineral has its own melting temperature. For example, tin melts when it gets more than twice as hot as boiling water. The melting point of silicon is almost five times as hot as molten tin. Since most rocks are mixtures of several minerals, the ingredients melt and separate at different temperatures. As the molten mixture cools, the minerals also freeze solid at different temperatures.

The most dramatic rock melting goes on down inside the earth. The average thickness of the earth's rocky crust is about 40 miles. It is somewhat like a shell, shattered into about six major and many smaller sections called plates. Where two plates rub together, pockets of molten rock called magma may form deep below the surface.

Now and then, mysterious stresses cause the magma to erupt in rivers of lava and fiery clouds of gases. On the surface, the molten lava soon cools to form granites and other igneous rocks. We are told that the infant earth was a mass of molten material. As it cooled, its lighter materials formed the solid crust.

The Bronze Age of human history began when people made tools and weapons of bronze. This alloy of copper and tin must be smelted, or melted, in furnaces that are four or five times hotter than boiling water. Our major metals are iron and steel    so we live in the Iron Age. And some of our blast furnaces reach temperatures of 3,000 degrees Fahrenheit.

Meantime the spaceways of the Solar Systems are populated with large and small meteors    made from planetary materials. Every day, thousands of them collide with the earth. As the average meteor falls through the atmosphere, it generates heat like a match striking sandpaper. The fiery heat from its molten minerals looks for all the world like a falling star.