When people discuss geology, the idea of strata is one of the first terms that is introduced. Strata, or the layers of material one can see when looking at cross-sections of the Earth, explain a great deal about the ways in which the land developed—and even when it was not land at all—in any given area. This is in some ways the book of the planet, the record of what has transpired, and when. The story of the first man in England to begin to talk about and map his country's strata is the story of The Map That Changed the World: William Smith and the Birth of Modern Geology.

It has not always been the case that ordinary people knew what strata were or why they are important. In fact, it has not always been the case that there were bonafide geologists studying such things. In England, a single man began to penetrate this realm of understanding on his own, by struggling with the meaning of the layers he spied in a mineshaft in Somerset. His name was William Smith, and he was born in 1769. Curiosity about the rocks around him and the Earth below him drove him to ask questions such as what these layers he saw on the mine walls meant. As he looked at the layers on the walls, he began to unravel a mystery that had troubled him for years, back above ground.

When he watched his uncle, a dairyman, weigh out his goods, he noticed that the object he used, called a pound-stone, did not look like a stone at all. Eventually, he identified it as a petrified sea urchin. But what was an artifact from the sea doing so far inland, he wondered? He got an answer to that question—and to many more—in that Somerset mine. At one time, this inland town was not inland at all but was part of the great oceans. That story and much more was revealed to Smith as he learned the book of the Earth written in the strata.

Smith eventually captured his observations on brilliant maps—brilliant both in the sense that they were very cleverly conceived and in terms of the electric colors used to illustrate them. Those maps became a cornerstone for modern geology and brought William Smith fame. The Map That Changed the World chronicles this explorer's great professional victories, as well as his personal tragedies.