Dirk Kalff, age 10, of Montreal West, Quebec, Canada, for his question:

WHAT EXACTLY IS PEAT MOSS?

Peat moss is the brown, spongy stuff with an earthy smell that gardeners add to their potting soil. Actually, it is a mixture of partly decayed plant fibers. It helps the soil by adding small pockets to hold air and moisture for thriving roots. As a rule, the peat moss recipe begins in a soggy swamp, where masses of waterweeds tangle themselves with moisture and mud.

This goes on for ages, and generations of weeds add thick layers of decaying vegetation to the marshy mud. This is called peat or peat moss, because some of the vegetation resembles the springy mosses. In some parts of the world, people dig it out, dry it in the sun and use it as a fragrant fuel in their stoves. When left alone for a few million years, layers of peat become buried and compressed.

Finally they are changed into layers of glossy black coal.