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  Telling Time    
Paths to the Past
Telling Time
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      Archaeologists tell time in two ways. Consider this problem. In many, if not most places in Illinois, if you dug a hole, say one meter deep, you would find different layers of dirt. If the layers of dirt have not been disturbed, which layer is older, one near the ground surface or one at the bottom of your hole? The answer: the deeper layer is older. Now lets say you found an artifact on the ground surface and one in the layer at the bottom of your hole. Which artifact is oldest? Right! The one found in the deeper layer. Archaeologists call this relative dating. In others words, although they do not know the precise age of the layer of dirt or the artifacts, they can say that one artifact is older or younger than another. Until the middle of the 20th century, relative dating was the only way archaeologists could tell time.

About fifty years ago, a chemist discovered how to determine when an ancient plant or animal had died. All plants and animals contain carbon atoms. There are different forms of carbon atoms, one of which is slightly radioactive. When a plant or animal dies, the radioactive carbon begins to decay at a relatively steady rate. By measuring the amounts of the different forms of carbon in a bone, shell, wood and other plant material, scientists can calculate how long ago death occurred. Archaeologists call this absolute dating. In other words, using this means of telling time, archaeologists can determine the precise age of a layer of dirt and the artifacts it contains, if the layer also contains objects with the different forms of carbon.

With the means to tell time, archaeologists could identify different cultures, most simply defined as different ways of life. And they could study why cultures changed. In Illinois, archaeologists divide the ancient past into several cultures expressed in the following general framework.

14,000 to 12,000 years ago, or 12,000 to 10,000 B.C.
12,000 to 3,000 years ago or 10,000 to 1,000 B.C.
3,000 to 1,250 years ago or 1,000 B.C. to A.D. 750
1,250 to 550 years ago or A.D. 750 to A.D. 1450
550 to 350 years ago or A.D. 1450 to A.D. 1650
(less than 350 years ago or A.D. 1650)

Where did these names come from? Paleo-Indian is from the Greek word, palaio, meaning ancient. Archaic is from the Greek word, arkhaikos, meaning old fashioned. Archaeologists use the word to refer to a way of life prior to the widespread use of pottery. Woodland refers to a way of life that developed in the woodlands east of the Mississippi River. And Mississippian refers to a different way of life that appears in the Mississippi River valley. Protohistory is the study of a culture just prior to its earliest recorded history. The Historic Period begins with the arrival of French explorers, Pere Marquette and Louis Jolliet, in 1673.


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