The geologic time scale is a system we use to measure and describe the history of Earth, which is approximately 4.6 billion years old. The time scale is helpful because it measures how long Earth has

The geologic time scale is a system we use to measure and describe the history of Earth, which is approximately 4.6 billion years old. The time scale is helpful because it measures how long Earth has existed, describes how Earth has developed and recognizes major events that occurred on Earth. Scientists determine the number and length of time periods based on important events in Earth’s history.