Joan Hart, age 12, of Monroe, Michigan, for her question:

How are fossils preserved so long?

The great destroyers of possible future fossils are bacteria which cause organic material to rot and decay. Mites and various types of soil insects also play a part in breaking down and decomposing animal remains. When these decay causing creatures can¬not do their work the hard bones and teeth of a departed animal have a chance to remain in the ground, perhaps for many millions of years, and become fossils.

Bacteria and other creatures that cause decay are living things that require oxygen and a certain amount of moisture. They are foiled most successfully in situations where the animal remains are buried quickly. Swampy areas of stagnant water, quick¬sand bogs and pits of sticky tar where animals become trapped and buried and where there is little oxygen to support decay bacteria are good fossil locations. So are river bottoms and the restless seabed of the worldwide oceans.