John Shafer, age 10, of Williamsport, Pennsylvania, for his question:

How much coal does the world use a year?

The big coal mining countries are Russia, the United States and Germany    though many other countries produce sizeable amounts. Together, the world mines more than three billion tons of coal every year. Most of it is consumed in the fiery furnaces of industry. Some is burned to create steam for generating electricity. Some is broken down into the simple molecules used to make plastics and dozens of other everyday products.

The coal we use every year can never be replaced    and the earth has only so much of it. Some people say that we are burning too much coal and soon the supplies will all be gone. But geologists estimate that the earth has enough buried coal to last the world for another 1,500 years. However, some of these known reserves are buried at great depths and some are in dusty fragments.