Geologists estimate Earth is at least 4.6 billion years old. What if all those years were compressed into one calendar year?
Geologists divide the record of Earth’s past into segments—eons, eras, periods, and epochs—to make studying and understanding billions of years of geologic history more manageable.
Terms used to describe units of geologic time and the rock layers formed during those time intervals provide a common language for talking about the past.
Mass extinctions, extraordinary events in evolutionary history, have taken place at least five times in the last 500 million years.