Chapter 7 Exam Review
Which of the following correctly lists two key pieces of evidence that, together, indicate that we should expect human activity to cause global warming?
(1) Carbon dioxide tends to make planets warmer than they would be otherwise; (2) Measurements demonstrate that human activity is raising the carbon dioxide concentration in the atmosphere.
Explain why liquid water is not stable on Mars today, but why we nonetheless think it flowed there in the distant past.
Liquid water is not stable on the surface of Mars today because of the cold temperatures and the low atmospheric pressure. The low temperature means that water is almost always frozen on Mars today. However, if it did warm enough to thaw, the low pressure would cause the water to almost immediately evaporate off of the surface. Water might exist below the surface, however, where the planet is still warm enough for it to exist in liquid form. We see lots of evidence for liquid water in the past. Evidence includes networks of what look like river channels, lots of erosion of features like craters, layers in rocks seen by landers, and chemical evidence indicating that some of the rocks were formed in water.
Why does Earth have so little carbon dioxide in its atmosphere compared to Venus?
Earth has just as much carbon dioxide as Venus, but most of it is locked up in carbonate rocks rather than being free in the atmosphere.
What is the importance of the carbon dioxide (CO2) cycle?
It regulates the carbon dioxide concentration of our atmosphere, keeping temperatures moderate.
Which describes our understanding of flowing water on Mars?
It was important once, but no longer.
Earth has been gradually warming over the past few decades. Based on a great deal of evidence, scientists believe that this warming is caused by _____.
human activities that increase the concentration of greenhouse gases in Earth's atmosphere
The oxygen in Earth's atmosphere was released by
life.
Where is the most CO2 that has outgassed from Earth's volcanoes?
locked up in rocks
Which two factors are critical to the existence of the carbon dioxide (CO2) cycle on Earth?
plate tectonics and liquid water oceans Carbon dioxide dissolves in the oceans and becomes incorporated into carbonate rock; plate tectonics recycles the carbonate rock into the mantle, where it melts and releases its gas back to the atmosphere.
In the context of planetary geology, what do we mean by outgassing?
the release by volcanism of gases that had been trapped in a planetary interior
Which of the following is a strong greenhouse gas?
water vapor
Suppose that Earth's atmosphere had no greenhouse gases. Then Earth's average surface temperature would be __________.
well below the freezing point of water
Which of the following is the most basic definition of a greenhouse gas?
a gas that absorbs infrared light
What do we mean by a runaway greenhouse effect?
a greenhouse effect that keeps getting stronger until all of a planet's greenhouse gases are in its atmosphere
The reason that small planets tend to lose interior heat faster than larger planets is essentially the same as the reason that __________.
a large baked potato takes longer to cool than a small baked potato,A smaller object has proportionally more surface area through which to lose its interior heat.
What is a magnetosphere?
a region of space around a planet in which the planet's magnetic field can trap charged particles
Suppose we represent Earth with a basketball. On this scale, most of the air in Earth's atmosphere would fit in a layer that is _________.
about the thickness of a sheet of paper
Which of the following best describes how the greenhouse effect works?
A planet's surface absorbs visible sunlight and returns this absorbed energy to space as infrared light. Greenhouse gases slow the escape of this infrared radiation, which thereby heats the lower atmosphere.
Why is the sky blue (on Earth)?
Because molecules scatter blue light more effectively than red light
Which of the following is not a similarity between Earth and Mars? Both planets have similar day lengths. Both planets have similar atmospheric pressure. Both planets have a similar axis tilt and therefore both have seasons. Both planets have polar caps.
Both planets have similar atmospheric pressure.
Suppose Earth were to cool down a little. How would the carbon dioxide cycle tend to restore temperatures to normal?
Cooler temperatures lead to slower formation of carbonate minerals in the ocean, so carbon dioxide released by volcanism builds up in the atmosphere and strengthens the greenhouse effect.
Describe the key ways in which the atmosphere affects Earth. What is the greenhouse effect, and how does it work?
Earth's atmosphere stops harmful X rays and UV radiation from reaching the surface. The energy of these photons is absorbed in the atmosphere and heats the layers when the light is absorbed. Ozone is a molecule that is very good at absorbing UV light; even small amounts in our stratosphere are enough to block most harmful UV light. The atmosphere also stops meteors and energetic particles. Furthermore, the presence of an atmosphere causes weather and erosion. The greenhouse effect causes the surfaces of planets to be warmer than they would be without an atmosphere. The effect occurs because the light coming down to a planet's surface is visible and generally passes through atmospheres with little absorption. However, the planet's surface, being cooler than the Sun's, emits infrared radiation that can be absorbed by certain molecules called greenhouse gases. The atmosphere then radiates the energy in all directions, some of it back down to the planet again, reheating the surface a bit.
All the following statements about Mars are true. Which one might have led to a significant loss of atmospheric gas to space?
Mars lost any global magnetic field that it may once have had.
Describe the leading hypothesis for how Mars lost much of its atmosphere some 3 billion years ago, and identify the role played by Mars's size.
Mars may have lost atmospheric gases through solar wind stripping. Early in Mars's life this effect was probably not important, thanks to Mars's magnetic field. However, as the planet cooled and convection stopped, the magnetic field would have disappeared, leaving the planet vulnerable to the solar wind particles. With little or no outgassing to replenish the atmosphere (because there would be no internal convection to drive volcanism), the atmosphere would have disappeared. If this scenario is correct, it is the small size of Mars that is to blame for the loss of atmosphere. Had Mars been a larger planet, it would have stayed hotter longer and convection would have continued.
Recent evidence suggests that Mars once had a global magnetic field. Assuming this is true, which of the following could explain why Mars today lacks a global magnetic field like that of Earth?
Mars's interior has cooled so much its molten core layer no longer undergoes convection.Convection of the molten core is required for a global magnetic field.
What do we conclude if a planet has few impact craters of any size?
Other geological processes have wiped out craters.
What is outgassing, and how did it lead to the existence of Earth's atmosphere and oceans?
Outgassing is the process in which gases from a planet's interior are expelled through volcanism. This process is very important to our existence since it probably supplied most of the water on our surface and in our atmosphere.
Briefly summarize the evidence linking human activity to global warming. What are its potential consequences?
Over the past few decades, it has become clear that the Earth's temperature is rising. We also know that the amount of carbon dioxide in our atmosphere is increasing. Since humans burn fossil fuels for energy, a process that releases carbon dioxide, it's apparent that we are responsible for the rising levels of carbon dioxide. Since carbon dioxide is a greenhouse gas, the evidence shows that we are therefore responsible for causing the Earth to warm. The effects of significant warming would be devastating to humans. Sea levels would rise significantly, flooding coastal areas. Global warming would also alter weather patterns, which could make some currently food-producing areas deserts. We might also see intensified storms due to global warming. In addition, there are secondary effects such as changes in ecologies or ocean currents. These are more difficult to predict, unfortunately.
Which heat source continues to contribute to Earth's internal heat?
Radioactive decay
What makes us think that Mars must once have had an atmosphere that was warmer and had higher surface pressure?
The atmosphere is too cold and thin for liquid water today, yet we see evidence that water flowed on the surface in the past.
Which of the following general statements about Earth's atmosphere is not true? Gas high in the atmosphere absorbs dangerous X rays from the Sun. The oxygen in our atmosphere was released by living organisms. Without the relatively rare gas called ozone, Earth's surface would be bathed in dangerous ultraviolet light from the Sun. The nitrogen and oxygen in Earth's atmosphere keep the surface pleasantly warm.
The nitrogen and oxygen in Earth's atmosphere keep the surface pleasantly warm.
Which of the following best explain what we think happened to outgassed water vapor on Venus?
Ultraviolet light split the water molecules, and the hydrogen then escaped to space. This did not occur on Earth, because the temperatures allowed the water vapor to condense into liquid water and rain down to the surface.
Which terrestrial world has the most atmospheric gas?
Venus
All of the statements below are true. Which one gives the primary reason why the surface of Venus today is some 450°C hotter than the surface of Earth? Venus has a much stronger greenhouse effect than Earth. Venus is only about 73% as far from the Sun as Earth. Venus has a higher atmospheric pressure than Earth. Venus has a much higher reflectivity than Earth.
Venus has a much stronger greenhouse effect than Earth.
Which of the following is an example of convection?
Warm air expanding and rising while cooler air contracts and fall.
