Exam 3

The following images show the four terrestrial planets in our solar system. Rank the planets from left to right based on the strength of the greenhouse effect occurring at their surfaces, from strongest to weakest.

Strongest to Weakest: Venus, Earth, Mars, Mercury

Suppose that Earth's atmosphere had no greenhouse gases. Then the Earth's average surface temperature would be _________.

Some 30°C cooler, which means well below the freezing point of water

All of the following statements are true. Which one provides strong observational support for the claim that greenhouse gases make a planet warmer than it would be otherwise?

Venus has a higher average temperature than Mercury. The fact that Venus is hotter than Mercury despite being nearly twice as far from the Sun tells us that its thick carbon dioxide atmosphere must warm it significantly—just as we expect from the theory of the greenhouse effect.

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.

Based solely on an understanding of the greenhouse effect (as displayed in the figure), which one of the following statements is true?

We should expect an increase in the greenhouse gas concentration to lead to global warming. The evidence discussed in this tutorial makes it clear that greenhouse gases make a planet's surface warmer than it would otherwise be, so we should expect a rise in the greenhouse gas concentration to make Earth warmer. It is possible that there can be mitigating factors through feedbacks, but the basic link between greenhouse gas concentration and global warming is very strong.

Suppose you find a meteorite made almost entirely of metal. According to current science, which of the following statements must be true?

Your meteorite is a fragment from the core of a large asteroid that shattered in a collision.

A rock found on Earth that crashed down from space is called _________.

a meteorite

What do we mean by a primitive meteorite?

a piece of rock that is essentially unchanged since it first condensed and accreted in the solar nebula some 4.6 billion years ago It's called primitive because the word means "first."

Which of the following is not a piece of evidence supporting the idea that an impact caused the mass extinction that occurred 65 million years ago?

Fossilized dinosaur bones contain fragments of rock from the impact.

Suppose we discover a new comet on an orbit that brings it closer to the Sun than Mercury every 125 years. What can we conclude?

It has been on its current orbit for only a very short time compared to the age of our solar system.

On the graphs shown, you can identify an ice age by looking for __________.

a trough (bottom of a dip) on the temperature graph The graph shows that one ice age ended only about 10,000 years ago, and there have been numerous other ice ages during the past 400,000 years.

The Huygens probe took numerous pictures as it descended to Titan's surface in 2005. What did the pictures show?

features or erosion, including what appeared to be dry river valleys and lakebeds

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 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.

The two most important processes in heating the interiors of the terrestrial worlds are:

(1) Heat deposited by the process of formation; (2) heat released by radioactive decay.

A correlation means that two things go up and down together. In this case, there is a correlation between the temperature and the carbon dioxide concentration because both were generally high at the same times in the past and low at the same times in the past.

1. We understand the physical mechanism of the greenhouse effect, through which carbon dioxide can increase a planet's temperature. 2. Models of the greenhouse effect successfully predict the temperatures of Venus and Mars from their atmospheric carbon dioxide amounts. 3. Models of Earth's climate that include recent increases in the carbon dioxide concentration match observed temperature increases better than those that do not include it. Together, the success of the models and our clear understanding of the mechanism of the greenhouse effect leave little room for doubt that carbon dioxide is indeed a cause of higher temperatures on a planet.

Earth's temperature remains fairly steady, which means that Earth must return the same amount of energy to space that it receives from the Sun. In what forms does Earth return most of this energy to space?

1. visible light reflected by the surface 2. visible light reflected by clouds 3. infrared light emitted by the surface and atmosphere The total amount of energy returned to space in these three forms of radiation equals the amount of energy that reaches Earth in the form of sunlight.

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.

Asteroid

A relatively small and rocky object that orbits a star; asteroids are officially considered part of a category known as "small solar system bodies".

Tidal Heating

A source of internal heating created by tidal friction. It is particularly important for satellites with eccentric orbits such as Io and Europa.

Which of the following is not a piece of evidence supporting the idea that Europa may have a subsurface ocean?

Astronomers have detected small lakes of liquid water on Europa's surface.

Which of the following is NOT a piece of evidence supporting the idea that Europa may have a subsurface ocean?

Astronomers have detected small lakes of liquid water on Europa's surface. Astronomers have not detected water on Europa's surface.

Which of the following gases is NOT a significant ingredient of the jovian planet atmospheres?

Carbon dioxide

Listed following are some distinguishing characteristics of comets, meteors, and asteroids. Match these to the appropriate category of objects.

Comets: *form a coma when near the sun *most are located either in the Kuiper belt or the Oort cloud *visible in the sky as a fuzzy patch of light that rises and sets with the stars Meteors: *visible in the sky as a bright streak of light for only a few seconds *dust particles entering Earth's atmosphere at high speed Asteroids: *compositions similar to that of the terrestrial planets *typically orbit the Sun at approximately 3 AU

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.

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.

Which moon is considered likely to have a deep, subsurface ocean of liquid water?

Europa

The following images show four types (wavelengths) of light. Rank these from left to right based on the amount of each that is emitted (as thermal radiation) by Earth's surface, from greatest to least. If you think that two (or more) types should be ranked as equal, drag one on top of the other(s) to show this equality.

Greatest Amount to Least Amount: infrared, (ultraviolet, visible, X-ray) Earth emits thermal radiation characteristic of its surface temperature, which means it is almost entirely infrared (extending, in principle, down into the radio). For Earth, the surface temperature is too low to emit any visible, ultraviolet, or X-ray light, so those are all ranked equally. (Note: Technically, thermal emission extends over all wavelengths, so even at low temperatures there might be an occasional photon of visible or higher-energy radiation. However, this emission is negligible for Earth, which is why we rank them all equal to zero.)

In Part A, you found that Earth emits only infrared light. This infrared light can be absorbed by greenhouse gases, such as carbon dioxide and water vapor, in the atmosphere. In fact, all the terrestrial planets emit infrared light from their surfaces. The following images show the four terrestrial planets in our solar system. Rank these planets from left to right based on the total amount of infrared-absorbing greenhouse gases in their atmospheres, from greatest to least.

Greatest Greenhouse Gas Abundance to Least Greenhouse Gas Abundance: Venus, Earth, Mars, Mercury Venus has a thick atmosphere of carbon dioxide. Earth has greenhouse gases primarily in the form of water vapor, carbon dioxide, and methane. Mars has an atmosphere made mostly of carbon dioxide, but its atmosphere is so thin that it contains less total greenhouse gas than Earth's atmosphere. Mercury has essentially no atmosphere at all.

Which internal heat source still generates heat within the terrestrial worlds today?

Heat from radioactive decay.

Based on our understanding of Titan as discussed in the text, which of the following is unlikely to be found on Titan?

Lakes of liquid water in the warmer equatorial regions Studies of Titan show that its surface temperature is never anywhere close to being warm enough for liquid water, even at its equator.

The following images show the four terrestrial planets in our solar system. Rank the planets from left to right based on the amount by which the greenhouse effect increases their surface temperatures, compared to what their temperatures would be without the greenhouse effect, from largest to smallest increase

Largest Increase to Smallest Increase: Venus, Earth, Mars, Mercury A stronger greenhouse effect means a greater temperature increase, which is why the rankings here are the same as the rankings for Parts B and C. The differences are quite extreme: Mercury has no greenhouse effect, so its temperature is determined solely by its distance from the Sun and its reflectivity. The greenhouse effect raises the temperature of Mars by about 6°C from what it would be otherwise; it raises Earth's temperature by about 31°C (which means our planet would be frozen over without the greenhouse effect); and it raises Venus's temperature by about 510°C, explaining the extremely high temperature of Venus.

Assuming that features you see on Mars are similar to features found on Earth, what would a casual inspection of the interactive photo of Mars lead you to suspect about water on Mars?

Surface water only exists as frozen ice. There is nothing on the brownish surface to suggest liquid water, and close-up photos confirm that there is no liquid water on Mars today. However, the prominent polar caps look much like Earth's polar caps, and would therefore make you suspect that they are made of water ice. In fact, they contain both frozen carbon dioxide and frozen water.

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. If water really did flow, the atmospheric conditions must have been different.

Based on the evidence that atmospheric carbon dioxide is a cause of planetary warming, what aspect of the graphs should most concern us?

The carbon dioxide concentration today is significantly higher than at any time in the past 400,000 years and is rapidly rising. Therefore, if past trends continue, we would expect Earth's temperature to rise substantially as a result of this increase in the carbon dioxide concentration.

Which of the following would NOT be an expected consequence of global warming?

The entire Earth will warm up by the same amount. Global warming will change weather patterns, so some places may get cooler even as the Earth as a whole warms up.

Many scientists suspect that Venus has a stronger and thicker lithosphere than Earth. If this is true, which of the following could explain it?

The high surface temperature that has "baked out" all the liquid water from Venus's crust and mantle

Which of the following general statements about Earth's atmosphere is not true?

The nitrogen and oxygen in Earth's atmosphere keep the surface pleasantly warm.

Greenhouse Effect

The process by which greenhouse gases in an atmosphere make a planet's surface temperature warmer than it would be in the absence of an atmosphere.

Fermi's Paradox

The question posed by Enrico Fermi about extraterrestrial intelligence--"So where is everybody?"--which asks why we have not observed other civilizations even though simple arguments would suggest that some ought have spread throughout the galaxy by now.

Notice that the peaks and troughs on the temperature graph occur at the about the same times as peaks and troughs on the carbon dioxide graph. What can we infer from this fact alone?

There is a correlation between the carbon dioxide concentration and the global average temperature. A correlation means that two things go up and down together. In this case, there is a correlation between the temperature and the carbon dioxide concentration because both were generally high at the same times in the past and low at the same times in the past.

According to scientists, the naturally occurring greenhouse effect makes Earth about 31∘C warmer than it would be if there were no greenhouse gases in our atmosphere. How do scientists "know" what Earth's temperature would be without greenhouse gases?

They calculate this temperature from Earth's reflectivity and distance from the Sun. Aside from the greenhouse effect, the only factors that affect a planet's average temperature are its reflectivity and distance from the Sun. Since both distance and reflectivity have been measured, the expected temperature can be calculated easily and precisely. (Note that this assumes that the Sun's total emission of energy remains steady; measurements and theory both indicate that it varies very little over time scales less than a few million years.)

Which moon has a thick atmosphere made mostly of nitrogen?

Titan

Greenhouse gases in the atmosphere, such as carbon dioxide and water vapor, make Earth warmer than it would be otherwise because these gases __________.

absorb infrared light emitted by the surface Although the absorbed infrared light is quickly reemitted, it is reemitted in a random direction. As a result, greenhouse gases tend to slow the escape of infrared light from Earth to space, so that there is more heat (which means more energy) in the atmosphere than there would be if the infrared light escaped directly to space.

Which of the following is most unlikely to be found on Titan?

lakes of liquid water in the warmer equatorial regions

A typical meteor is created by a particle about the size of a _________.

pea We do not see the particle itself, but rather the flash of light it generates as it enters (and burns up in) the atmosphere at high speed.

The average temperature over the past 1000 years has been about 15∘C. From the graphs, you can conclude that Earth's average temperature during the past 400,000 years has __________.

varied between about 7∘C and 19∘C The zero level on the graph represents the 15∘C average temperature over the past millennium, so the peaks near +4 on the graph represent a temperature of about 15∘C+4∘C=19∘C and the troughs near −8 represent 15∘C−8∘C=7∘C.

The energy that warms Earth's surface comes primarily in the form of __________.

visible light from the Sun