4Think of all the animals and plants on Earth today. There are millions! But, in the history of Earth there are many more that have gone extinct. In this colorful volume, readers get a crash course in how and why a species may become extinct. Including understandable information about what scientists believe happened when life began, evolution, the dinosaurs, and how all of these plays a role in the ecosystems of today, this book is essential to the young reader's science library.