When you think about the old spark plug in this way you have just been making the beginnings of what we call an archeological _interpretation_; you have been making the spark plug tell a story. It is the same way with the man-made things we archeologists find and put in museums. Usually, only a few of these objects are pretty to look at; but each of them has some sort of story to tell. Making the interpretation of his finds is the most important part of the archeologist’s job. It is the way he gets at the “sort of history of human activity” which is expected of archeology. SOME OTHER SCIENTISTS There are many other scientists who help the archeologist and the physical anthropologist find out about prehistoric men. The geologists help us tell the age of the rocks or caves or gravel beds in which human bones or man-made objects are found. There are other scientists with names which all begin with “paleo” (the Greek word for “old”). The _paleontologists_ study fossil animals. There are also, for example, such scientists as _paleobotanists_ and _paleoclimatologists_, who study ancient plants and climates. These scientists help us to know the kinds of animals and plants that were living in prehistoric times and so could be used for food by ancient man; what the weather was like; and whether there were glaciers. Also, when I tell you that prehistoric men did not appear until long after the great dinosaurs had disappeared, I go on the say-so of the paleontologists. They know that fossils of men and of dinosaurs are not found in the same geological period. The dinosaur fossils come in early periods, the fossils of men much later. Since World War II even the atomic scientists have been helping the archeologists. By testing the amount of radioactivity left in charcoal, wood, or other vegetable matter obtained from archeological sites, they have been able to date the sites. Shell has been used also, and even the hair of Egyptian mummies. The dates of geological and climatic events have also been discovered. Some of this work has been done from drillings taken from the bottom of the sea. This dating by radioactivity has considerably shortened the dates which the archeologists used to give. If you find that some of the dates I give here are more recent than the dates you see in other books on prehistory, it is because I am using one of the new lower dating systems. [Illustration: RADIOCARBON CHART The rate of disappearance of radioactivity as time passes.[1]]