Time, Prehistoric

Prehistory is the time prior to written records. It includes not only human existence prior to written records, but also that of other forms of life. Since there are no written records, most of the information gathered about these earlier life forms is acquired through interpretation of fossils and artifacts left behind. These fossils may include human-made tools, whether stone or metal; animal bones; and coprolite, or fossilized excrement. Coprolite offers an insight into the dietary practices of animals and early humans. The study and interpretation of these fossils and artifacts is done by prehistoric archaeologists, and 99% of what is known today about human prehistory is through prehistoric archaeology. The earliest written records appeared around 5,000 years ago in Mesopotamia; 4,000 years ago in Greece; and 3,000 years ago in China. Prehistory ends differently for different cultures, since it is based on the advent of written records.

A number of methods are used in dating materials from prehistoric sites. Dendrochronology, or the study and use of tree rings as a method for dating events, is good for measuring changes in climate, beginnings of agrarian culture, and volcanic activity. Another way of dating fossils is through means of biostratigraphy: the study of fossil records and the surrounding strata in which they appear compared to those of other fossils. Although this method does not suggest a definite date, it does allow scientists to group fossils of the same time period together.

Carbon dating is also a commonly used method. All living things have carbon in them at the same ratio as the carbon in the atmosphere. Plants obtain carbon from the atmosphere through photosynthesis, whereas animals obtain carbon from the atmosphere by eating plants or animals that eat plants. Radiocarbon will cease to be created when an animal dies, at which point carbon-14 will begin breaking down at a constant rate. By measuring the amount of carbon-14 remaining in a corpse against the amount of carbon-12 in it, scientists can give an approximate age of a corpse. Due to outside influences and possible discrepancies in dating techniques, scientists will synchronize their findings with tree rings when possible. This is very important because the margin of error for carbon-14 dating can be as great as 2,000 years.