Billy Bob Alford, age 10, of Mexico, Missouri, for his question:

How lone does it take the earth to form coal?

Most of our beds of buried coal started to form in the earth's Carboniferous Period. This geological period began about 265 million years ago and lasted some 55 million years. Coal, of course, is formed from masses of plants and layers of vegetation. The story of our coal began with the strange forests of bhe Carboniferous Period. In those days, there were no flowers, no woody trunks or spreading branches. The biggest plants were tall tree ferns and giant horsetails. There were mosses and often the ancient forest stood in a swamp of soggy waterweeds.

The fantastic forest flourished perhaps for millions of years. At last it died and its remains were buried under ages of dirt and perhaps a few landslides. Underground, the heat and the crushing weight changed the old vegetation stage by stage into coal. It became soft brown peat material, then soft brown coal. After perhaps 250 million years, it became shiny black coal. Hard anthracite coal takes ages longer to form. And if the layer remains buried for another 100 million years or so, the heat and pressure change the coal to waxy black graphite.