For hundreds of years, people found the fossils of ancient sea creatures at the tops of tall mountains. Scientists puzzled over this problem. A fish couldn't have swum up a mountain. And how could rocks on a mountain move up from the bottom of a sea? Geologists finally found the answers they needed in the 1960s, when they developed the theory of plate tectonics. This theory revolutionized our understanding of the earth. Plate tectonics explains how volcanoes form, why earthquakes happen, and what goes on deep inside the earth to make the continents move. This book tells the story of scientists and their discoveries to explain how the theory of plate tectonics came to be.