"The geologic time scale is a way that scientists work to understand the timespan of our planet based on empirical and fossil-based evidence. This evidence is then used to try and place events in Earth’s history. Many things on our planet, such as the formation of mountains, or the draining of lakes by rivers, take millions of years. The creation of life on earth and the extinction of life on earth has happened many times over. Scientists have documented at least 5 mass extinctions. "