p. 605 CYU 2-7

2.Identify which of the following gases is most abundant in Earth’s atmosphere today. a. argonc. oxygen b. nitrogend. carbon dioxide 2. Nitrogen is most abundant in Earth’s atmosphere today. p. 605 CYU Compare Earth’s early atmosphere with its present atmosphere. 3. Earth’s early atmosphere was composed of many gases that would be poisonous to us today. As life forms evolved and began to photosynthesize, oxygen was produced. Once animals adapted to breathing oxygen, they began to give off carbon dioxide, balancing the production of oxygen.

4.Arrange the steps of the oxygen-carbon dioxide cycle in the correct order: a.Animals breathe oxygen b.Plants produce oxygen c.Plants use carbon dioxide d.Animals exhale carbon dioxide 4. The correct order is b, a, d, c. b. Plants produce oxygen a. Animals breathe oxygen d. Animals exhale carbon dioxide c. Plants use carbon dioxide p. 605 CYU 2-7

5. Explain why the following statement is incorrect: global warming could cause oceans to rise, so the greenhouse effect must be eliminated completely. 5. If we were to eliminate the greenhouse effect completely, the world’s climate would become too cold for humans to survive. p. 605 CYU 2-7

6. Predict how much colder it is at the top of Mount Everest, which is almost 9km above sea level, than it is at the Indian coastline. Consider only the difference in altitude. (Hint: the temperature in the troposphere decreases by 6°C/km) 6. The temperature at the top of Mount Everest is about 54°C colder. 9km x 6°C/km = 54°C

7. In 1982, Larry Walters rose to an altitude of approximately 4900m (just over 3 miles) on a lawn chair attached to 45 helium-filled weather balloons. Give two reasons why Walters’s efforts were dangerous. 7. Walters’s efforts were dangerous because the oxygen content of the air is considerably lower at that altitude and the temperature is extremely cold. p. 605 CYU 2-7