What is a fossil? Sometimes it's the imprint of an ancient leaf in a rock. Sometimes it's a woolly mammoth, frozen for thousands of years in the icy ground. Sometimes it's the skeleton of a stegosaurus that has turned to stone. A fossil is anything that has been preserved, one way or another, that tells about life on Earth. But you can make a fossil, too—something to be discovered a million years from now—and this book will tell you how.