Laurie Bragdon, age 13, of Portland, Me., for her question:

WHAT EXACTLY IS AIR?

Air surrounds the earth. It seems like nothing but it is really several gasses mixed together. Without air there couldn't be life on earth.

Air has no color, no smell and no taste. Yet air is just as real as land or water.

Air has weight, and it is this weight that keeps lighter than air balloons in the air. Air resistance keeps birds and planes up in the air.

Nitrogen makes up slightly more than 78 percent of dry air by volume. Oxygen makes up almost 21 percent. The remaining 1 percent is made up mostly of the gas argon with small amounts of the following gases: neon, helium, hydrogen, ozone, carbon dioxide, methane and other gases. Often there are also particles of dust and moisture in the air.