A fossil is the prehistoric remains of a plant or animal. Fossils are typically preserved when they are buried under many layers of sand and mud. Under great pressure the sand and mud become sedimentary rock. Minerals seep into the fossil replacing the organic matter and creating a replica in stone.
Articles & Books:
The Fossil Factory: A Kid's Guide to Digging Up Dinosaurs, Exploring Evolution, and Finding Fossils by Eldredge
Discovering Fossils : How to Find and Identify Remains of the Prehistoric Past by Frank A. Garcia
The World Encyclopedia of Fossils and Fossil-Collecting by Steve Parker
Fossil by Paul D. Taylor
Fossils by Douglas Palmer
The Best Book of Fossils, Rocks, and Minerals by Chris Pellant