Reflection Questions 1. How long (in centimeters and years) was the Precambrian period compared to the rest of the scale?

2. How many years and “centimeters” of time separated the dinosaurs and humans on Earth?

3. How many years and centimeters of time passed before life appeared on Earth?

4. For how many years of geologic time have humans existed?

5. Did dinosaurs exist at the same time as mammals? Explain your answer using the geologic time scale.