- Use the timeline to find out when fish, reptiles, birds, mammals, and humans appeared. What geological changes were occurring at the time of their appearance?
- How has the complexity of life changed over time?
- When did oxygen become part of Earth's atmosphere? What other changes occurred at the same time?
- List the major extinctions and the hypothesized causes of each.
- If you could trace your family back to early humans, how many generations would there be given a 50-year life span?
- What helps you understand deep time?
