What has happened through earth geologic history? Scientists have figured out a way to make a time scale by using rock sediment. By looking at a stacked arrangement of rocks, scientists can determine the age of fossils and rocks called a geologic column. Through this geologic column, scientist have been able to break the earth’s history down into different periods of time. The sediment found in rock layers can determine what the earth’s surface and climate was like at a given time in history. Scientists have given names to these certain points of time or eras in history.