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.
RADIOCARBON CHART
The rate of disappearance of radioactivity as time passes.[1]
[1] It is important that the limitations of the radioactive carbon “dating” system be held in mind. As the statistics involved in the system are used, there are two chances in three that the “date” of the sample falls within the range given as plus or minus an added number of years. For example, the “date” for the Jarmo village (see chart), given as 6750 ± 200 B.C., really means that there are only two chances in three that the real date of the charcoal sampled fell between 6950 and 6550 B.C. We have also begun to suspect that there are ways in which the samples themselves may have become “contaminated,” either on the early or on the late side. We now tend to be suspicious of single radioactive carbon determinations, or of determinations from one site alone. But as a fabric of consistent determinations for several or more sites of one archeological period, we gain confidence in the “dates.”