Explain how Earth and its atmosphere formed. 2. How is today’s atmosphere similar to and different from the early Earth’s atmosphere?

3. Describe how oxygen came to compose al-

most 21% of the atmosphere today.

4. Given that solar output had increased over the

past 4.6 billion years, how have Earth’s temperatures remained fairly constant over that

same time?

5. What is residence time and why is it important?

6. What is the carbon cycle and how does it

operate?

7. Describe the thermal structure of the

atmosphere.

8. What causes the thermal characteristics

associated with each thermal layer of the

atmosphere?

9. Compare and contrast the heterosphere and

the homosphere.

10. Why is there no defined top to the atmosphere?