1. How does energy from the Sun drive the movement of water from the oceans to the continents and back to the oceans again?

2. How might the ocean reduce the effects of fossil fuel combustion on CO₂ concentrations in the atmosphere?

3. Why is methane gas commonly produced in swamps?

4. Given that the bottom of the ocean is anaerobic, what process in the nitrogen cycle is likely to be occurring in this location?

5. How might nitrogen-fixing bacteria living in symbiosis with a plant affect the types of environments in which the plant could live?

6. Why is the weathering of bedrock responsible for such a small fraction of the nutrients available to plants?

7. Why do tropical and temperate soils have different rates of nutrient regeneration?

8. Explain why agricultural soils in boreal Canada retain their nutrients for many more years than agricultural soils in tropical South America.

9. How might global warming cause the release of CO₂ from boreal forest soils?

10. What is the chain of events in which the dumping of raw sewage into the Mississippi River leads to fish kills in the dead zone in the Gulf of Mexico?