Chapter 5 - Terrestrial Worlds
Listed following are characteristics of the atmospheres of Venus, Earth, and Mars. Match each atmospheric characteristic to the appropriate planet.
(1.) Venus: sulfuric acid clouds, almost no surface winds, runaway greenhouse effect. (2.) Earth: atmosphere composed primarily of nitrogen, ultraviolet-absorbing stratosphere. (3.) Mars: extremely low density atmosphere, global dust storms.
Formation of Lunar Maria
- Early surface is covered with craters - Large impact crater weakens crust. - Heat build-up allows lava to well up to surface. - Cooled lava is smoother and darker than surroundings.
Click the third tab (labeled "Global Warming"), then explore the graph and the expanded views you will find by clicking the "?" buttons. Which of the following statements are supported by the data shown?
- Earth's global average temperature has generally risen over the past century - Rises in global average temperature tend to be closely associated with rises in atmospheric carbon dioxide concentration - Atmospheric carbon dioxide levels have risen dramatically over the past century
All the following statements are true. Which two represent the two facts that lead us to expect Earth to be warming up as a result of human activity? Be sure to choose two of the statements below.
- Human activity is increasing the concentration of carbon dioxide and other greenhouse gases in the atmosphere. - Greenhouse gases make Earth warmer than it would be otherwise
Core
- Inner core and outer core - Composed mainly of iron and smaller amounts of nickel (solid in the inner core due to high pressure, liquid in the outer core due to lower pressure) - Convection currents in the outer core cause magnetic behavior
Percival Lowell's claims of a Martian civilization generated great public interest, but other scientists of his time were highly skeptical of these claims. Which two of the following statements (which are all true) explain why other scientists of the late 19th and early 20th centuries rejected Lowell's claims?
- Lowell's canals did not appear in photographs of Mars taken through telescopes. - Lowell's canals followed perfectly straight lines for thousands of kilometers.
Make a prediction: If the rise in carbon dioxide concentration continues at its current pace, the concentration in the year 2050 will be about _____ parts per million.
460
Using only pencil and paper calculations, Arrhenius concluded that a doubling of the carbon dioxide concentration would raise global temperatures by about _____.
5° C
Which of the terrestrial worlds has the strongest magnetic field?
Earth
In Part A, you found that Planet Z should not have polar ice caps or liquid water. What single change to Planet Z's characteristics would allow it to have these things?
A greater distance from its star
Temperature and Distance
A planet's distance from the Sun determines the total amount of incoming sunlight.
Temperature and Rotation
A planet's rotation rate affects the temperature differences between day and night.
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.
Runaway Greenhouse Effect
A runaway greenhouse effect would account for why Venus has so little water.
Which pair of Terrestrial planets are the most similar geologically?
Earth and Venus
Since the time Arrhenius made his prediction, the carbon dioxide concentration has risen by about 30% and the global average temperature has risen by about 1°C. Which statement below best describes how scientists should evaluate Arrhenius's prediction?
Although Arrhenius's prediction was not exact, the actual change is similar enough to the predicted change to validate the general idea that a rising carbon dioxide concentration would lead to global warming.
Changes in Greenhouse Gases
An increase in greenhouse gases leads to warming, while a decrease leads to cooling
Which of the following is not an expected consequence of the rising carbon dioxide concentration or global warming?
Animal deaths due to carbon dioxide poisoning.
The image below shows a rock formation nicknamed "the face on Mars" that was taken by the Viking 1 orbiter in 1976. Given the clear resemblance to a face, what is an appropriate scientific reaction to this image?
Assume it is most likely a coincidental result of light and shadow, and plan higher resolution follow-up observations.
Impact craters are formed by:
Asteroids or Comets
In what way is Venus most similar to Earth?
Both planets are nearly the same size.
Of the four gases CO2, H2O, N2, and O2, which are greenhouse gases?
CO2 and H2O
Aurora
Charged particles from solar wind energize the upper atmosphere near magnetic poles, causing an aurora.
Why is Mars red?
Chemical reactions between surface rock and atmospheric oxygen literally rusted the surface.
Click the fourth tab (labeled "Computer Models"), then explore how the graph changes as you click among the three buttons to its left. What is the primary message of the full graph (with all three curves shown)?
Climate models successfully reproduce the major recent trend in temperature data only if both human and natural factors are included.
Dry Riverbeds?
Close-up photos of Mars show what appear to be dried-up riverbeds.
Modeling of Climate Change
Complex models of global warming suggest that recent temperature increase is consistent with human production of greenhouse gases.
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.
As you found in Part A, early Mars had both core convection and a strong magnetosphere. What is the connection between these two things?
Core convection helps generate a magnetic field, and the magnetic field creates the magnetosphere.
Erosion of Craters
Details of some craters suggest they were once filled with water.
The ______ allows us to determine how fast Mars is moving toward or away from us.
Doppler Effect
Each of the following statements was either true for Mars in the distant past (early Mars) or is true for Mars today. Sort the statements by dragging each into the correct bin.
Early Mars: - Some craters held lakes of water. - Strong greenhouse Effect-Substantial volcanism and outgassing. - Strong magnetosphere. -Core convection Mars Today: - Surface pressure too low for stable liquid water - Very weak greenhouse Effect - Solar wind strips atmospheric gas
Which of the following best describes the geological histories of the Moon and Mercury?
Early in their histories, they suffered many impacts and experienced some volcanism and tectonics, but they now have little geological activity at all.
Erosion by Ice
Glaciers carved the Yosemite Valley.
Crater Walls
Gullies on crater walls suggest occasional liquid water flows have happened less than a million years ago.
The tallest mountain on Mars is called ___________
Olympus Mons
Which of the following Mars surface features provides dramatic evidence that volcanism has played a role in shaping the surface of Mars?
Olympus Mons
Seafloor Recycling
Seafloor is recycled through a process known as subduction.
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.
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 800,000 years and is rapidly rising.
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.
What is differentiation?
This is the sort of material in the molten planets by density
The long, deep canyon running along the equator is called _______
Valles Marineris
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 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.
Venus, Earth, Mars, Mercury
Erosion by Wind
Wind wears away rock and builds up sand dunes.
Which of the following statements about X-rays and radio waves is not true?
X-rays travel through space faster than radio waves.
Volcanism is more likely on a planet that
has high internal temperatures
Which of the following are forms of light (electromagnetic radiation)?
microwaves ultraviolet radio waves infrared X rays visible light gamma rays
Which two factors are critical to the existence of the carbon dioxide (CO2) cycle on Earth?
plate tectonics and liquid water oceans
Which of the following best describes the lunar maria?
relatively smooth, flat plains on the Moon
What observational evidence supports the idea that Mercury once shrank by some 20 kilometers in radius?
the presence of many long, tall cliffs
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
Earth's temperature remains fairly steady, which means that Earth must return nearly 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?
- infrared light emitted by the surface and atmosphere - visible light reflected by clouds - visible light reflected by the surface
Which internal heat source still generates heat within the terrestrial worlds today?
heat from radioactive decay
Listed below are geographic features of the terrestrial worlds. In each case, identify the geological process: impact cratering, volcanism, erosion, or tectonics (where tectonics is any large-scale processes affecting the structure of the planetary crust), most responsible for the feature described. Match the geographic feature to the appropriate geologic process.
(1.) Volcanism: big island of Hawaii, smooth surfaces of the lunar maria, Mars's Olympus Mons. (2.) Impact cratering: old surface features of the lunar highlands. (3.) Erosion: Earth's Grand Canyon. (4.) Tectonics: current locations of Earth's continents, Mars's Valles Marineris, Mercury's many long, tall cliffs.
Although the data show only a correlation between the carbon dioxide concentration and the global average temperature, scientists have other reasons to think that a rise in the carbon dioxide concentration actually causes a rise in the global average temperature. All of the following statements are true. Which statements lend support to the idea that carbon dioxide is a cause of planetary warming?
- Models of the greenhouse effect successfully predict the temperatures of Venus and Mars from their atmospheric carbon dioxide amounts. - We understand the physical mechanism of the greenhouse effect, through which carbon dioxide can increase a planet's temperature. - 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.
Go to the screen in the interactive figure called "Major Geological Features." Which of the following statements about the Tharsis Bulge, often simply called "Tharsis," are true?
- One end of Valles Marineris is connected to Tharsis. - Tharsis has higher elevation than surrounding regions - Tharsis has several large volcanoes.
Sources of Gas
- Outgassing from volcanoes - Evaporation of surface liquid; sublimation of surface ice - Impacts of particles and photons
Mantle
- Rocky layer - Makes up about 84% of the Earth's volume - Composed of hot, iron-rich silicate rocks that can actually flow, even though they are solid
Lava and Volcanoes
- Runny lava makes flat lava plains. - Slightly thicker lava makes broad shield volcanoes. - Thickest lava makes steep stratovolcanoes.
Go to the screen "Key Evidence of Water," and and select the feature called "Recurring Slope Lineae." Study this feature at each of the four zoom levels offered, and be sure to view the animation called "recurring slope linaea (gif)" that you will see at the third zoom level. Which of the following statements are true?
- The recurring slope lineae look like narrow dark streaks. - The recurring slope lineae are found among impact craters. - The recurring slope lineae appear to grow in spring and summer.
Start on the home screen of the interactive figure, with "Elevation is off." Then turn elevation on, and compare what you see. You may wish to switch back and forth between elevation on and off a few times. Then select the statements below that are true. Note: Features such as impact craters that are actually round in shape are distorted into oval shapes at mid- to high-latitudes by map projection effects.
- There is a large, roundish region of low-elevation in the southern hemisphere. - Several large volcanoes are found near or somewhat north of Mars's equator. - There is a long, deep canyon that strectches along a region close to Mars's equator. - Most of the northern hemisphere has much lower elevation than the southern hemisphere.
Losses of Gas
- Thermal escape of atoms - Sweeping by solar wind - Condensation onto surface - Chemical reactions with surface - Large impacts blasting gas into space
Click on the first tab at the top of the interactive figure (labeled "The Greenhouse Effect"), then explore what happens as you click among the buttons (labeled "none," "low," "medium," and "high") that adjust the greenhouse gas concentration. Which of the following occur as the greenhouse gas concentration increase?
- more infrared light is absorbed in the lower atmosphere - the average surface temperature rises
Consider a planet orbiting another star that is very similar to our Sun. Assume the planet is about the size of Earth and has an Earth-like orbit around its star. Which of the following statements are true about the light coming from the star and planet?
- the planet emits virtually all its light as infrared light - the star's spectrum peaks in visible light - the star emits much more light than the planet
Carbon Dioxide Cycle
1. Atmospheric CO2dissolves in rainwater. 2. Rain erodes minerals that flow into ocean. 3. Minerals combine with carbon to make rocks on ocean floor. 4. Subduction carries carbonate rock down into mantle. 5. Rock melts in mantle and CO2is outgassed back into atmosphere through volcanoes.
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.
Shown following are three terrestrial planets of our solar system. Rank the planets based on the amount of time the surface of the planet has had a moderate to high level of volcanic/tectonic activity, from longest to shortest.
Earth, Mars, Mercury
Arrhenius was not particularly alarmed by his discovery at the time. What changed that made later scientists become much more concerned about the climate effects of carbon dioxide?
Emissions of carbon dioxide rose much faster than Arrhenius had anticipated.
Erosional Debris
Erosion can create new features such as deltas by depositing debris
What motivated Arrhenius to calculate how changes in carbon dioxide might affect the climate?
He was seeking to understand the causes of ice ages.
The large, roundish, low-elevation region in the southern hemisphere is called _______
Hellas Basin
Changes in Reflectivity
Higher reflectivity tends to cool a planet, while lower reflectivity leads to warming.
Seismic Waves
How do we know what's inside Earth? • Vibrations that travel through Earth's interior tell us what Earth is like on the inside. • P waves go through Earth's core, but S waves do not. • We conclude that Earth's core must have a liquid outer layer.
Plate Motions
Measurements of plate motions tell us past and future layout of the continents.
Each of the following statements is best associated with one of the four major geological processes. Drag each statement into the correct bin for its associated process.
Impact Cratering - Mostly occurred during heavy bombardment. - Affected all solid worlds similarly. Volcanism - Created the smooth lunar maria. - Erased virtually all craters on Io. - Responsible for the existence of Earth's atmosphere and oceans. Tectonics - On Earth, involves motion of plates. - Includes surface compression that builds mountains. Erosion - Includes features sculpted by wind.
Incandescent light bulbs emit thermal radiation because their filaments are heated to about 2500 Kelvin. LED light bulbs emit only at particular visible wavelengths. Why do incandescent bulbs require more energy to shine with the same amount of visible light as LED bulbs?
Incandescent bulbs emit most of their energy as infrared light.
What key process underlies why Mars changed so much from its early conditions to its conditions today?
Interior cooling.
Why does the Earth have a magnetic field?
It has a molten charged core that rotates
Volcanoes on Venus
It has many volcanoes, including both shield volcanoes and stratovolcanoes.
As discussed in the video, the leading hypothesis for why Mars changed holds that interior cooling led to loss of its magnetosphere, allowing the solar wind to strip atmospheric gas away. How has the MAVEN mission provided evidence for this hypothesis?
It has measured rates of gas loss from the atmosphere today.
What happens to the energy that the ground absorbs in the form of visible sunlight?
It is returned upward in the form of infrared light.
On a cloudless day, what happens to most of the visible light headed toward Earth?
It reaches Earth's surface, where some is reflected and some is absorbed.
Why does Mars appear reddish in color?
It reflects most of the Sun's red light while absorbing most of its blue light.
What is the importance of the carbon dioxide (CO2) cycle?
It regulates the carbon dioxide concentration of our atmosphere, keeping temperatures moderate.
Imagine being on the Moon and looking at the thermal radiation spectrum of Earth. How would it compare to the spectra shown on the graph in the video?
It would be very similar to the spectrum of the human.
Which of the following most likely explains why Venus does not have a global magnetic field like Earth?
Its rotation is too slow.
Radar Mapping
Its thick atmosphere forces us to explore Venus's surface through radar mapping.
Earth's Magnetosphere
Magnetic field of Earth's atmosphere protects us from charged particles streaming from Sun (the solar wind).
Hydrogen Content
Map of hydrogen content (blue) shows that low-lying areas contain more water ice.
All of the following statements are true. Which one explains why Mars has lost so much more interior heat than Earth.
Mars is smaller than Earth.
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.
Martian Rocks
Mars rovers have found rocks that appear to have formed in water.
Shown below are the four terrestrial planets of our solar system. Assume that all the planets started out equally hot inside. Rank the planets based on their expected cooling rates, from fastest cooling to slowest cooling.
Mercury, Mars, Venus, Earth
Rank the five terrestrial worlds in order of size from smallest to largest.
Moon, Mercury, Mars, Venus, Earth
When were the heat-trapping effects of gases that cause the greenhouse effect first measured by scientists?
More than 150 years ago.
Suppose we had a device that allowed us to see Earth's interior. If we looked at a typical region of the mantle, what would we see happening?
Not much-on human time scales, the mantle looks like solid rock.
Erosion on Venus
Photos of rocks taken by landers show little erosion.
Each statement below represents a feature that has been claimed to exist on Mars. Sort the statements into the correct bin according to whether each is a feature that actually exists, that does not actually exist, or that might exist but about which we cannot yet draw a definitive conclusion.
Real Mars: 1. Minerals of types known to form in liquid water 4. abundant water ice 5. dried-up river beds Imaginary Mars: 2. surface pools of liquid water 6. a network of straight-line canals 7. cities built by an ancient civilization 9. frequent rainfall and snowfall Uknown Mars: 3. microscopic life 8. underground pockets of liquid
Tectonics on Mars
The system of valleys known as Valles Marineris is thought to originate from tectonics.
Which of the following best describes why we say that light is an electromagnetic wave?
The passage of a light wave can cause electrically charged particles to move up and down.
______ is a high-elevation region dotted by tall volcanoes.
Tharsis Bulge
Erosion by Water
The Colorado River continues to carve Grand Canyon.
Which of these objects is NOT geological dead??
The Earth
Hot Spots
The Hawaiian islands have formed where a plate is moving over a volcanic hot spot
Suppose that Mars had a higher surface temperature. How would its spectrum be different?
The peak in the infrared would be at shorter wavelength.
Solar Brightening
The Sun very gradually grows brighter with time, increasing the amount of sunlight warming the planets.
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.
Seasons on Mars
The ellipticity of Mars's orbit makes seasons more extreme in the southern hemisphere.
Which of the following is not an expected consequence of global warming?
The entire Earth will warm up by the same amount.
Most of the Moon's surface is densely covered with craters, but we find relatively few craters within the lunar maria. What can we conclude?
The maria formed after the heavy bombardment ended.
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.
Under what circumstances can differentiation occur in a planet?
The planet must have a molten interior.
Tectonics on Venus
The planet's fractured and contorted surface indicates tectonic stresses.
Go to the screen "Mars Mission Landing Sites," and and select Opportunity landing site (2004). Explore all five zoom levels offered, making sure to read the captions at the tops of the screens. Based on the information provided, why was the landing site,called Meridiani Planum, chosen for the Opportunity mission?
The region was already known to have minerals likely to have formed in liquid water.
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.
Now click the second tab (labeled "Terrestrial Planet Temperatures"), then explore what happens as you click the button that allows you to add or remove greenhouse gases. Which terrestrial planet would have its surface temperature the most dramatically changed if its greenhouse gases were removed from its atmosphere? Now click the second tab (labeled "Terrestrial Planet Temperatures"), then explore what happens as you click the button that allows you to add or remove greenhouse gases. Which terrestrial planet would have its surface temperature the most dramatically changed if its greenhouse gases were removed from its atmosphere? Mercury
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.
Cratering on Venus
Venus has impact craters, but fewer than the Moon, Mercury, or Mars.
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.
Venus, Earth, Mars, Mercury
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.
Venus, Earth, Mars, Mercury
The following images show the four terrestrial planets in our solar system. Rank these planets from left to right based on the atmospheric pressure at the surface, from highest to lowest. (Not to scale.)
Venus, Earth, Mars, Mercury
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 gas in their atmospheres, from most to least.
Venus, Earth, Mars, Mercury
Outgassing
Volcanism also releases gases from Earth's interior into the atmosphere.
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.
In Part A, you found that Planet Z should not have strong winds and violent storms. What single change to Planet Z's characteristics would cause it to have strong winds and violent storms?
a faster rotation rate
Which of the following is the most basic definition of a greenhouse gas?
a gas that absorbs infrared light
Suppose we use a baseball to represent Earth. On this scale, the other terrestrial worlds (Mercury, Venus, the Moon, and Mars) would range in size approximately from that of __________.
a golf ball to a baseball
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
In Part A, you found that Planet Z should not have seasons. What single change to Planet Z's characteristics would cause it to have seasons?
a larger axis tilt
Scientists suspect that Mars once had abundant liquid water on its surface. For this to have been true, early Mars must have had __________ than Mars today.
a much higher atmospheric pressure and much stronger greenhouse effect
According to the laws of thermal radiation, hotter objects emit photons with __________.
a shorter average wavelength
On the graphs shown, you can identify an ice age by looking for __________.
a trough (bottom of a dip) on the temperature graph
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
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
Carbon dioxide in Mars's atmosphere produces _____ in the infrared portion of its spectrum
absorption lines
Based on Planet Z's size, orbital distance, and rotation rate, which of the following properties is it likely to have?
active tectonics, an atmosphere produced by outgassing, active volcanoes
Scientists have confidence in the predictions of today's best climate models because they __________.
agree well with actual data for recent decades
What kind of surface features may result from tectonics?
all of the above
What would happen to Earth's temperature if Earth were more reflective? a) It would go up. b) It would go down. c) It wouldn't change.
b) It would go down.
Why is the sky blue (on Earth)?
because molecules scatter blue light more effectively than red light
From center to surface, which of the following correctly lists the interior layers (defined by density) of a terrestrial world?
core, mantle, crust
Why is the sky blue? a) The sky reflects light from the oceans. b) Oxygen atoms are blue. c) Nitrogen atoms are blue. d) Air molecules scatter blue light more than red light. e) Air molecules absorb red light.
d) Air molecules scatter blue light more than red light.
What is the main reason why Venus is hotter than Earth? a) Venus is closer to the Sun than Earth. b) Venus is more reflective than Earth. c) Venus is less reflective than Earth. d) Greenhouse effect is much stronger on Venus than on Earth. e) Human activity has led to declining temperatures on Earth.
d) Greenhouse effect is much stronger on Venus than on Earth.
If Earth didn't have an atmosphere, what would happen to its temperature? a) It would go up a little (less than 10°C). b) It would go up a lot (more than 10°C). c) It would go down a little (less than 10°C). d) It would go down a lot (more than 10°C). e) It would not change.
d) It would go down a lot (more than 10°C).
How does the cooling of planets and potatoes vary with size? a) Larger size makes it harder for heat from inside to escape. b) Larger size means a bigger ratio of volume to surface area. c) Larger size takes longer to cool. d) all of the above
d) all of the above
The core, mantle, and crust of a planet are defined by differences in their
density
What is necessary for differentiation to occur in a planet? a) It must have metal and rock in it. b) It must be a mix of materials of different density. c) Material inside must be able to flow. d) All of the above e) b and c
e) b and c
Hot gas in Mars's upper atmosphere produces ___ in the ultraviolet portion of its spectrum.
emission lines
We divide the electromagnetic spectrum into six major categories of light, listed below. Rank these forms of light from left to right in order of increasing wavelength. To rank items as equivalent, overlap them.
gamma rays X rays ultraviolet visible light infrared radio waves
You have found that Planet Z should have active tectonics and volcanism and an atmosphere produced by volcanic outgassing. What single factor explains why the planet should have these characteristics?
has a large size for a terrestrial planet.
Earth has been gradually warming in recent decades, and very strong evidence indicates that the cause of this warming is __________.
human activities that are increasing the concentration of greenhouse gases in Earth's atmosphere
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 are increasing the concentration of greenhouse gases in Earth's atmosphere
Go to the screen in the interactive figure called "Key Evidence of Water," then zoom in on the "Southern Highlands." Which geologic processes are most clearly evident in the southern highlands?
impact cratering and erosion
The processes responsible for virtually all surface geology are __________.
impact cratering, volcanisms, tectonics, and erosion
Scientists can estimate the age of a planetary surface by counting __________.
impact craters
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.
infrared, (UV, visible, X-ray)
Rank the forms of light from left to right in order of increasing speed. To rank items as equivalent, overlap them.
infrared, visible light, gamma rays, ultraviolet, radio waves, X rays ALL THE SAME SPEED
The greenhouse effect raises Earth's surface temperature (from what it would be otherwise) because the infrared light radiated by Earth's surface __________.
is absorbed by greenhouse gases, slowing the escape of this energy to space
Based on all we know about the terrestrial worlds, what single factor appears to play the most important role in a terrestrial planet's geological destiny?
its size
Which of the following is the underlying reason why Venus has so little wind erosion?
its slow rotation
Thermal radiation gets its name because __________.
its spectrum depends on the temperature of the object emitting it
Suppose you know the frequency of a photon and the speed of light. What else can you determine about the photon?
its wavelength and energy
There are no auroras on Venus because it
lacks a strong magnetic field
Red light has a _____ wavelength and a _____ frequency than does blue light.
longer, lower
Which two factors are most important to the existence of plate tectonics on Earth?
mantle convection and a thin lithosphere
The cores of the terrestrial worlds are made mostly of metal because ________.
metals sunk to the centers a long time ago when the interiors were molten throughout
Suppose that you had "X-ray vision" that allowed you to see X rays. What would you notice when you looked at a friend standing near you that you could not notice with your visible light vision alone?
nothing
What are the two geological features that appear to set Earth apart from all the other terrestrial worlds?
plate tectonics and widespread erosion
Thermal radiation is defined as __________.
radiation with a spectrum whose shape depends only on the temperature of the emitting object
If you have a telescope that is observing light with wavelengths of a few meters, you are observing __________.
radio waves
Rank the forms of light from left to right in order of increasing energy. To rank items as equivalent, overlap them.
radio waves infrared visible light ultraviolet X rays gamma rays
Rank the forms of light from left to right in order of increasing frequency. To rank items as equivalent, overlap them.
radio waves infrared visible light ultraviolet X rays gamma rays
X ray photons have a _____ wavelength, _____ frequency, and _____ energy than do ultraviolet photons.
shorter, higher, higher
Compared to a cold object, a hotter object of the same size emits most of its light at __________ wavelengths and emits _____ light overall.
shorter, more
Which region of Earth has warmed the most in recent decades?
the Arctic
Which of the following is not a key line of evidence supporting the hypothesis that Mars once had abundant liquid water on its surface?
the canals of Mars mapped in the 19th century by Percival Lowell
Which of the following describes tectonics?
the disruption of a planet's surface by internal stresses
Which of the following describes volcanism?
the eruption of molten rock from a planet's interior to its surface
Which of the following describes impact cratering?
the excavation of bowl-shaped depressions by asteroids or comets striking a planet's surface
The lithosphere of a planet is the layer that consists of
the rigid rocky material of the crust and uppermost portion of the mantle.
Which of the following describes erosion?
the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather
We determine Mars's surface temperature from the peak wavelength of the ___ it emits.
thermal radiation
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 800,000 years has __________.
varied between about 7∘C and 19∘C
The energy that warms Earth's surface comes primarily in the form of __________.
visible light from the Sun
The color of Mars in our sky is determined by the ____ of Mars's spectrum
visible portion
Suppose that Earth's atmosphere had no greenhouse gases. Then Earth's average surface temperature would be ________.
well below the freezing point of water
The relatively few craters that we see within the lunar maria
were formed by impacts that occurred after those that formed most of the craters in the lunar highlands.
What are the circumstances under which convection can occur in a substance?
when the substance is strongly heated from underneath
CO2 Concentration
• Global temperatures have tracked CO2 concentration for last 500,000 years. • Current CO2 concentration is the highest it's been in at least 500,000 years. • Most of the CO2increase has happened in last 50 years!
Differentiation
• Gravity pulls high-density material to center. • Lower-density material rises to surface. • Material ends up separated by density. • A planet's outer layer of cool, rigid rock is called the lithosphere. • It "floats" on the warmer, softer rock that lies beneath.
Changes in Axis Tilt
• Greater tilt creates more extreme seasons, while smaller tilt keeps polar regions colder. • Small gravitational tugs from other bodies in solar system cause Earth's axis tilt to vary between 22°and 25°.
Temperature and Reflectivity
• A planet's reflectivity (or albedo) is the fraction of incoming sunlight it reflects. • Planets with low albedo absorb more sunlight, leading to hotter temperatures.
Rocks
• A rock is an aggregate of minerals—a physical mixture. The three categories of rock reflect how they were formed: - Igneous • Formed from cooling and crystallization of magma (molten rock that forms inside Earth), or lava (is molten rock erupted at Earth's surface) - Sedimentary • Formed from preexisting rocks subjected to weathering and erosion - Metamorphic • Formed from preexisting rock transformed by heat, pressure, or chemical fluids
Earth's Atmosphere
• About 10 kilometers thick • Consists mostly of molecular nitrogen (N2) and oxygen (O2).
What causes geological activity?
• Accretion and differentiation when planets were young • Radioactive decay is most important heat source today What causes geological activity? • Convection transports heat as hot material rises and cool material falls. •Conduction transfers heat from hot material to cool material. •Radiation sends energy into space.
What is an atmosphere?
• An atmosphere is a layer of gas that surrounds a world
Terrestrial Planet Interiors
• Applying what we have learned about Earth's interior to other planets tells us what their interiors are probably like.
Changing Axis Tilt
• Calculations suggest Mars's axis tilt ranges from 0°to 60°. • Such extreme variations can cause climate changes. • Alternating layers of ice and dust in polar regions reflect these climate changes.
Long-Term Climate Change
• Changes in Earth's axis tilt might lead to ice ages. • Widespread ice tends to lower global temperatures by increasing Earth's reflectivity. • CO2 from outgassing will build up if oceans are frozen, ultimately raising global temperatures again.
Earth's Magnetic Field
• Convection currents in the molten part of the Earth's interior create Earth's magnetic field • Magnetic north and magnetic south flip every 10,000 to 20,000 years - Evidence: layering of sedimentary rock • Geographic north is actually magnetic south, and geographic south is actually magnetic north - North pole of the compass is attracted to it • Charged particles coming from outer space (cosmic rays) get caught in the magnetic field of Earth, and make up Van Allen radiation belts. The disturbances in the field allow particles to move and bounce, causing them to emit radiation and glow (aurora borealis and aurora australis)
Tectonics
• Convection of the mantle creates stresses in the crust called tectonic forces. • Compression of crust creates mountain ranges. • Valley can form where crust is pulled apart.
Earth's Thermostat
• Cooling allows CO2to build up in atmosphere. • Heating causes rain to reduce CO2in atmosphere.
Earth's Interior
• Core: highest density; nickel and iron • Mantle: moderate density; silicon, oxygen, etc. • Crust: lowest density; granite, basalt, etc.
Ice in Polar Craters
• Deep craters near the lunar poles show evidence of water ice. • Possible on Mercury as well.
Atmospheres of Other Planets
• Earth is only planet with a stratosphere because of UV-absorbing ozone molecules (O3). • Those same molecules protect us from Sun's UV light.
Global Warming
• Earth's average temperature has increased by 0.5°C in past 50 years. • The concentration of CO2is rising rapidly. • An unchecked rise in greenhouse gases will eventually lead to global warming.
Plate Tectonics on Earth
• Earth's continents slide around on separate plates of crust. • Motion of the continents can be measured with GPS.
Earth's Water and CO2
• Earth's temperature remained cool enough for liquid oceans to form. • Oceans dissolve atmospheric CO2, enabling carbon to be trapped in rocks.
Erosion
• Erosion is a blanket term for weather-driven processes that break down or transport rock. • Processes that cause erosion include: - glaciers - rivers - wind
Continental Drift
• German naturalist Alfred Wegener proposed in 1915 that the world's continents were once joined together as a single super continent called Pangaea • This idea was supported by geologic, biologic, and climatologic evidence • The boundary of each continent is not at its shoreline but at the edge of its continental shelf (gently sloping platform that leads to the ocean floor) • In 1950s the idea of continental drift was accepted when migration of magnetic poles was discovered
Surface Area-to-Volume Ratio
• Heat content depends on volume. • Loss of heat through radiation depends on surface area. • Time to cool depends on surface area divided by volume: • Larger objects have a smaller ratio and cool more slowly. - 4 pi r^2 / (4/3 pi r^3) = 3/r
How is human activity changing our planet?
• Human-made CFCs in the atmosphere destroy ozone, reducing protection from ultraviolet radiation. • Human activity is driving many species to extinction. • Human use of fossil fuels produces greenhouse gases that can cause global warming.
What processes shape planetary surfaces?
• Impact cratering - Impacts by asteroids or comets • Volcanism - Eruption of molten rock onto surface • Tectonics - Disruption of a planet's surface by internal stresses • Erosion - Surface changes made by wind, water, or ice
Light's Effects on Atmosphere
• Ionization: removal of an electron • Dissociation: destruction of a molecule • Scattering: change in photon's direction • Absorption: photon's energy is absorbed. • X rays and UV light can ionize and dissociate molecules. • Molecules tend to scatter blue light more than red. • Molecules can absorb infrared light.
Tectonics on Mercury
• Long cliffs indicate that Mercury shrank early in its history.
Surface Features
• Major geological features of North America record the history of plate tectonics • The Himalayas formed from a collision between plates. • The Red Sea is formed where plates are pulling apart.
Was Earth's geology destined from birth?
• Many of Earth's features are determined by its size, rotation, and distance from Sun. • The reason for plate tectonics is not yet clear.
Volcanism on Mars
• Mars has many large shield volcanoes. • Olympus Mons is largest volcano in solar system.
Climate Change on Mars
• Mars has not had widespread surface water for 3 billion years. • Greenhouse effect probably kept the surface warmer before that. • Somehow Mars lost most of its atmosphere. • Magnetic field may have preserved early Martian atmosphere. • Solar wind may have stripped atmosphere after field decreased because of interior cooling.
Cratering of Mercury
• Mercury has a mixture of heavily cratered and smooth regions like the Moon. • Smooth regions are likely ancient lava flows. - The Rembrandt Basin is a large impact crater on Mercury. - Hollows in a crater floor created by escaping gases.
How do impact craters reveal a surface's geological age?
• Most cratering happened in the first billion years. • A surface with many craters has not changed much in 3 billion years.
Impact Cratering
• Most cratering happened soon after the solar system formed. • Craters are about 10 times wider than object that made them. • Small craters greatly outnumber large ones.
Nitrogen and Oxygen
• Most of Earth's carbon and oxygen is in rocks, leaving a mostly nitrogen atmosphere. • Plants release some oxygen from CO2 into atmosphere.
Why do some planetary interiors create magnetic fields? Sources of Magnetic Fields
• Motions of charged particles are what create magnetic fields. • A world can have a magnetic field if charged particles are moving inside. • Three requirements: - Molten, electrically conducting interior - Convection - Moderately rapid rotation
Minerals
• Naturally occurring (formed naturally rather than manufactured) • Crystalline solids, i.e. they have an orderly and repeating arrangement of atoms, ions, and/or molecules. • Specific chemical composition, with slight variations. • Generally inorganic (i.e. not part of a living body)
"Canals" on Mars
• Percival Lowell misinterpreted surface features seen in telescopic images of Mars.
Role of Distance from Sun
• Planets close to the Sun are too hot for rain, snow, ice and so have less erosion. • Hot planets have more difficulty retaining an atmosphere. • Planets far from the Sun are too cold for rain, limiting erosion. • Planets with liquid water have the most erosion.
Role of Rotation
• Planets with slower rotation have less weather, less erosion, and a weak magnetic field. • Planets with faster rotation have more weather, more erosion, and a stronger magnetic field.
Polar Ice Caps of Mars
• Residual ice of the south polar cap remaining during summer is primarily water ice. • Carbon dioxide ice of polar cap sublimates as summer approaches and condenses at opposite pole.
Dust Storms on Mars
• Seasonal winds can drive dust storms on Mars. • Dust in the atmosphere absorbs blue light, sometimes making the sky look brownish-pink.
Exospheres of the Moon and Mercury
• Sensitive measurements show that the Moon and Mercury have extremely thin atmospheres. • Gas comes from impacts that eject surface atoms.
Role of Planetary Size
• Smaller worlds cool off faster and harden earlier. • Larger worlds remain warm inside, promoting volcanism and tectonics. • Larger worlds also have more erosion because their gravity retains an atmosphere.
Role of Size
• Smaller worlds cool off faster and harden earlier. • The Moon and Mercury are now geologically "dead."
Lunar Maria
• Smooth, dark lunar maria are less heavily cratered than lunar highlands. • Maria were made by floods of runny lava.
Cratering of Moon
• Some areas of Moon are more heavily cratered than others. • Younger regions were flooded by lava after most cratering.
Consequences of Global Warming
• Storms more numerous and intense • Rising ocean levels; melting glaciers • Uncertain effects on food production, availability of fresh water • Potential for social unrest
Rifts, Faults, Earthquakes
• The San Andreas fault in California is a plate boundary. • Motion of plates can cause earthquakes.
Cratering on Mars
• The amount of cratering differs greatly across Mars's surface. • Many early craters have been erased
Continental Motion
• The idea of continental drift was inspired by the puzzle-like fit of the continents. • Mantle material erupts where the seafloor spreads.
Where does an atmosphere end?
• There is no clear upper boundary. • Most of Earth's gas is less than 10 kilometers from surface, but a small fraction extends to more than 100 kilometers. • Pressure and density decrease with altitude because the weight of overlying layers is less. • Altitudes more than 100 kilometers are considered "space." • Small amounts of gas are present even above 300 kilometers.
Effects of Atmospheres
• They create pressure that determines whether liquid water can exist on surface. • They absorb and scatter light. • They create wind, weather, and climate. • They interact with the solar wind to create a magnetosphere. • They can make planetary surfaces warmer through the greenhouse effect.
Seafloor Crust
• Thin seafloor crust differs from thick continental crust. • Dating of the seafloor shows that it is usually quite young.
Earth's Atmospheric Structure
• Troposphere: the lowest layer of Earth's atmosphere • Temperature drops with altitude. • Warmed by infrared light from surface and convection • Stratosphere:layer above the troposphere • Temperature rises with altitude in lower part, drops with altitude in upper part. • Warmed by absorption of ultraviolet sunlight • Thermosphere: layer at about 100 kilometers altitude • Temperature rises with altitude. • X rays and ultraviolet light from the Sun heat and ionize gases. • Exosphere: highest layer in which atmosphere gradually fades into space • Temperature rises with altitude; atoms can escape into space. • Warmed by X rays and UV light
Ozone and the Stratosphere
• Ultraviolet light can break up O2molecules, allowing ozone (O3) to form. • Without plants to release O2, there would be no ozone in stratosphere to absorb ultraviolet light.
Does Venus have plate tectonics?
• Venus does not appear to have plate tectonics, but entire surface seems to have been "repaved" 750 million years ago. • Weaker convection? • Thicker or more rigid lithosphere?
Atmosphere of Venus
• Venus has a very thick carbon dioxide atmosphere with a surface pressure 90 times that of Earth. • Slow rotation produces a very weak Coriolis effect and little weather. • Thick carbon dioxide atmosphere produces an extremely strong greenhouse effect. • Earth escapes this fate because most of its carbon and water is in rocks and oceans. • Reflective clouds contain droplets of sulphuric acid. • The upper atmosphere has fast winds that remain unexplained.
Greenhouse Effect
• Visible light passes through the atmosphere and warms a planet's surface. • The atmosphere absorbs infrared light from the surface, trapping heat. • A planet's surface temperature is determined by the balance between energy from sunlight it absorbs and energy of outgoing thermal radiation.
Volcanism
• Volcanism happens when molten rock (magma) finds a path through lithosphere to the surface. • Molten rock is called lava after it reaches the surface.
Weather and Climate
• Weather is the ever-varying combination of wind, clouds, temperature, and pressure. - Local complexity of weather makes it difficult to predict. • Climate is the long-term average of weather. - The long-term stability of climate depends on global conditions and is more predictable.
Four Important Questions
• Why did Earth retain most of its outgassed water? • Why does Earth have so little atmospheric carbon dioxide, unlike Venus? • Why does Earth's atmosphere consist mostly of nitrogen and oxygen? • Why does Earth have an ultraviolet-absorbing stratosphere?
Tectonic Features
• Wrinkles arise from cooling and the contraction of a lava flood. • Now the Moon is considered geologically "dead" because geological processes have virtually stopped.
