Problem 20
Decide whether each statement makes sense or does not make sense. Explain clearly; because not all of these have definitive answers, your explanation is more important than your chosen answer. Venus is not in the habitable zone now, but it may have been in the past.
Problem 21
Decide whether each statement makes sense or does not make sense. Explain clearly; because not all of these have definitive answers, your explanation is more important than your chosen answer. Venus is not in the habitable zone now, but a few billion years from now it will be.
Problem 22
Decide whether each statement makes sense or does not make sense. Explain clearly; because not all of these have definitive answers, your explanation is more important than your chosen answer. If we could somehow start plate tectonics on Venus, its surface would cool and it would regain the oceans it had in the past.
Problem 23
Decide whether each statement makes sense or does not make sense. Explain clearly; because not all of these have definitive answers, your explanation is more important than your chosen answer. Mars will someday undergo a runaway greenhouse effect and become extremely hot.
Problem 24
Decide whether each statement makes sense or does not make sense. Explain clearly; because not all of these have definitive answers, your explanation is more important than your chosen answer. We are not yet certain, but it is quite likely that Earth has suffered through a runaway greenhouse effect at least once in the past 4 billion years.
Problem 27
Decide whether each statement makes sense or does not make sense. Explain clearly; because not all of these have definitive answers, your explanation is more important than your chosen answer. The fact that additional atmospheric \(\mathrm{CO}_{2}\) must cause a greenhouse effect is all we need to know to link global warming to human activity.
Problem 28
Decide whether each statement makes sense or does not make sense. Explain clearly; because not all of these have definitive answers, your explanation is more important than your chosen answer. Earth has been warmer in the past than it is today, so there is nothing to worry about with global warming.
Problem 29
Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences. The habitable zone refers to (a) the regions of a planet where good weather allows life to exist; (b) the range of distances from a star where a planet's surface temperature is always above the freezing point of water; (c) the range of distances from a star within which water could exist in liquid form on a suitably sized planet.
Problem 30
Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences. A planet that is not within a habitable zone cannot have (a) life: (b) subsurface oceans; (c) abundant liquid water on its surface.
Problem 32
Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences. What is the likely reason for Venus's lack of water in any form? (a) The planet accreted little water during its birth. (b) The water is locked away in the crust. (c) The water was in the atmosphere, where molecules were broken apart by ultraviolet light from the Sun.
