Answer: Relative and absolute dating.
Step-by-step explanation:
The clues in rocks help scientists to know how Earth has changed. The geologic time scale was crated by scientists observed that classified and studied fossils from the oldest to the youngest sedimentary rock in what is called relative dating. After years of research they started to implement absolute dating, which consists on measuring the amounts of radioactive elements in rocks to determine the actual number of years old. The geologic time scale is divided into eons, eras, periods, and epochs.