Discover The Wonders of Our Earth and the forces and life forms that shape our world with the Physical Geography Series. Geologic Time refers to the millions or even billions of years in which the processes and forces that shape the earth took place. Learn why and how scientists use this time scale and why it is divided into Eras, Epochs and Periods. Explore how geologists use potassium-argon dating to determine the age of rocks and minerals. Visit Ohio State University’s dating lab and see the dating process in action. Subjects covered include: Difference between relative time scale and the atomic time scale, How earth scientists discovered the basic principles of geologic time, How geologists have divided earth history into ERAS and PERIODS, How geologists have determined the age of the earth, How meteorites are used to help determine the age of the earth.