"Archaeological Explorations." (Essay, Part 2).
Another type of chronometric dating is based on the law of radioactive decay. According to this law, the atoms of certain elements decompose in predictable ways. Three of the methods used are radiocarbon (carbon 14) dating. pottasium-argon dating. and fission-track dating. They are based on the predictable decomposition of the chemicals carbon, pottasium, and uranium respectively. If archaeologists can measure the amount of decay, then they can measure the time and date both important ancient objects and the areas where they are found.
Although chronometric dating is very important to archaeologists, it is not sufficient. They want to know not only how old a relic is, but also how it fits into human history. By using methods of relative dating, archaeologists can determine such facts as when and object was invented by a group of people and how the object was improved or replaced in the years after its invention. Thus, relative dating methods add a historical aspect to archaeological dating.
One method of relative dating is stratigraphic analysis. This method is used when a site has been occupied either continuously or periodically over a length of time. Many Middle Eastern cities, for example, were continuously inhabited for thousands of years. On the other hand, caves near the Hudson River in New York were occupied periodically. Sometimes many years passed between occupations of these hollow places in the sides of the Hudson River Valley. However, whether a site was continuously or periodically inhabited, the method of getting the raw material for a stratigraphic analysis remains the same. Archaeologists carefully excavate a site, noticing the strata, layers. Generally, the deeper the stratum, the older this layer is. Because each stratum yields remains, archaeologists can analyze the remains and discover the sequence of events at a site. (Essay, Part 2).
