Rabbits, cacti, bumblebees, jellyfish, penguins, sunflowers—all living things on the earth are the descendants of simple, single-celled organisms that lived more than 3½ billion years ago. There are millions of different kinds of plants and animals living on the earth. Many millions more lived here in the past. Where did they all come from? Why have some died out and others lived on?
HMH Books for Young Readers