Mark Dikeman, age 11, of Portland, Ore., for his question:

WHAT EXACTLY IS FIRE?

Heat and light that comes from a burning substance is called fire. A French chemist named Antoine Lavoisier discovered in 1777 that burning is the result of a rapid union of oxygen with other substances. Burning is also called combustion.

Not all substances burn the same way. Charcoal gives off heat with only a glow while wood, oil, coal and gas give off heat and a flame. All substances, however, do require oxygen for burning to take place.

To have fire you must first have fuel or a substance that will burn. The fuel must then be heated to its kindling temperature, and then there must be plenty of oxygen for the fire.