Stacy Wilcoxen, age 11, of Maquon, I11., for her question:
HOW DO ARCHAEOLOGISTS KNOW WHERE TO DIG?
Archaeology is the study of ancient buildings and other objects as a way of learning about the past. An archaeologist is a person who works like a detective and treats the things found as clues to the lives of the people who made and used them. Archaeology is usually considered to be a branch of anthropology, the scientific study of man.
When an archaeologist starts to look for a site where treasures of the past may be found, some locations are easy because they lie above ground. But most sites have been hidden below the surface by the weather and by years of neglect.
An archaeological site often comes to light entirely by chance. Natural causes, such as a river eroding its banks, may reveal ancient remains.
After a severe drought in the winter of 1853, the level of Lake Zurich in Switzerland fell so low that the foundation posts of prehistoric lake dwellings were revealed for the first time in thousands of years. Men going about their daily tasks, either plowing, digging foundations or making roads, sometimes find buried objects. Citizens in London came across ancient Roman walls when they cleaned up after the air raids of World War II.
Often an archaeologist will rely on early writings to help him fill in gaps in his knowledge. The Bible and the works of Homer have helped in the past.
Aerial photography is one of the most important modern methods used to find sites. Photographs taken from an airplane sometimes show traces of buried structures that are not visible at ground level. An aerial photo of a cornfield, for example, may show a line of taller, greener corn extending straight across a field. To the
archaeologist, this may mean that men once dug a ditch there. The ditch has filled up, but the soil covering it is still more fertile than the surrounding land. Aerial photos helped archaeologists discover ancient fields in Great Britain, irrigation canals in Mesopotamia and Etruscan cities in Italy.
The archaeologist also can locate buried objects with a resistivity survey. This survey is made by passing an electric current through the ground to measure the electrical resistance of the soil, which is affected by moisture. The stones of ancient buildings contain less moisture than the surrounding earth, and raise the electrical resistance.
In using a resistivity survey on an archaeology quest, sometimes the walls or posts of a buried structure may collect moisture and lower the resistance.
Soil analysis may also be used to detect sites of settlements of people who left no durable remains. This is because human refuse increases the phosphate content of the soil.
It is the archaeologist's job to determine the layout or over all plan of a site at each stage of the area's history and then establish a chronology or time sequence of things he finds.