The Earth is about 4.5 billion years old. This immense time span is divided up by the geological time scale. This scale is most detailed at the period when life was plentiful, as shown by fossils. And how do scientists determine when an era begins and when it ends?
how do scientists determine when an era begins and when it ends?
Major Geological Changes
Due to widespread extinction, scientists determine when an era starts and ends. Each major extinction kills around 90% of all creatures. This causes life to alter in a noticeable and dramatic manner. The fossil record, which displays extinct animals from Earth’s history, helps scientists estimate when significant changes occur.