As a land that's constantly in flux, Earth sometimes reveals clues about the plants, animals, and other organisms that lived long ago. Fossils teach us much about what life was like millions of years ago, answering the questions of how Earth changed and maybe even why it changed. This essential Earth science topic is thoroughly explained through manageable text, fact boxes, informational charts and diagrams, and a glossary and index. Readers will become young Earth detectives by the time they're through with this text.