To understand how relative and absolute geologic ages are determined. To introduce the central role of fossils in interpreting earth history. The geologic time scale shown in Fig. 1 is a product of placing rocks in their proper sequence of formation to form a composite record of geologic events.
History is a sequence of events placed in proper chronological order.
Placing geologic events in their proper chronological order was first done by building composite sections in one area and correlating these sections to other areas where the record could be compared and improved upon. This process has built the geologic column as we know it today. In the later half of the twentieth century, radiometric age dating techniques allowed geologists to determine absolute ages for this time scale, creating an absolute geologic time scale. Selective determination of absolute radiometric ages on important sections has allowed geologists to place ages of the geologic column, producing the geologic time scale. We will examine how relative and absolute geologic ages are determined.