Chapter 7: Earth
Which parts of the Sun's radiation are responsible for heating Earth's surface?
the visible and the infrared
Why is the sky blue?
the atmosphere scatters the light from the Sun
In noting that our world is "differentiated," we mean that
the iron and nickel core is denser than the silicate mantle and crust.
The Dynamo Theory holds that
magnetic fields are generated by rapidly spinning, fluid magnetic interiors
How do geologists use earthquakes to obtain information about Earth's interior?
When waves from earthquakes travel through the Earth's interior, properties of those waves, such as their intensity and speed, are changed by the materials they pass through. By seeing exactly how those properties change, geologists can determine the nature of the material in the interior.
What is Convection?
Convection is the rising of hot material through cooler material, which sinks.
What effect does it have on the Earth's atmosphere?
In the Earth's atmosphere, it transports heat from the surface into the upper atmosphere and is responsible for many of the weather patterns in the troposphere.
What effect doesit have on the Earth's interior?
In the Earth's interior, it causes the liquid magma in the mantle to be in constant motion, and is responsible for volcanism and plate tectonics.
Following an earthquake, how long would it take a P-wave, moving in a straight line with a speed of 5.0 , to reach Earth's opposite side?
According to the current understanding of Earth's magnetic field and how magnetic fields are generated, which two components in Earth's internal structure are required in order to generate a magnetic field?
The formal description of how planetary magnetic fields are generated is known as dynamo theory. According to this theory, a planetary magnetic field needs both a conducting liquid interior and a rapidly rotating core in order to generate a magnetic field. Earth's powerful magnetic field is produced through the interaction of the rapidly rotating inner core and conducting liquid, outer core.
Earth's magnetosphere acts as a protective shield against the dangerous, high-energy solar wind. The magnetosphere can be visualized as a large sheath surrounding Earth and extending out into space. Two important structures, known as the Van Allen belts, compose the inner regions of the magnetosphere and directly affect the auroral events seen on Earth. Label the appropriate regions of the inner magnetosphere.
The inner and outer Van Allen belts are doughnut-shaped zones of high-energy particles in Earth's magnetosphere. Earth's magnetic field lines converge at the magnetic axis that runs through the magnetic North and South poles. The aurora borealis, commonly called the Northern lights, and the aurora australis, commonly called the Southern lights, occur in the Northern and Southern hemispheres, respectively. Though the names are different, they refer to the same phenomenon viewed from different geographic regions on Earth.
An auroral event occurs due to the interaction between the solar wind, Earth's magnetosphere, and Earth's atmosphere. The following steps describe the process of events leading to the formation of an aurora. Rank the steps in sequence from first to last, in order of how they must occur.
The aurorae are generated through a sequence of events starting at the Sun and ending with a spectacular atmospheric light show on Earth. Divided into six steps, the process is as follows:
1.The solar wind particles traveling in Earth's direction interact with Earth's magnetosphere.
2.A small number of particles become trapped in the Van Allen belts.
3.The trapped particles spiral around within the magnetic field, where on occasion they collide with atoms in Earth's atmosphere.
4.The collision transfers energy and excites the atmospheric atoms.
5.The electrons in the excited atmospheric atoms are unstable and fall from their excited states back to the ground state.
6.The transitioning electrons release their energy in the form of light, producing the beautiful, atmospheric phenomenon known as the aurorae.
On a cloudless day, what happens to most of the visible light headed toward Earth?
Most visible light passes through our atmosphere, and this light heats the surface as it is absorbed.
On a day with complete cloud cover, what happens to the visible light headed toward Earth?
Clouds have a cooling effect because they reflect visible light. However, they do not reflect all of it; if they did, cloudy days would be dark as night.
What happens to the energy that the ground absorbs in the form of visible sunlight?
Remember that objects emit thermal radiation characteristic of their temperatures. Earth's surface has a temperature for which its thermal radiation peaks in the infrared. In other words, Earth absorbs energy from space in the form of visible light, and returns this energy to space in the form of infrared light.
The greenhouse effect raises Earth's surface temperature (from what it would be otherwise) because the infrared light radiated by Earth's surface __________.
This absorption and reemission means that the infrared light follows a much longer path through the atmosphere until it reaches space than it would without greenhouse gases. In essence, the greenhouse gases keep more infrared light in the atmosphere at any one time, thereby raising the temperature from what it would be otherwise.
We currently believe that Earth's structure is made up of six main regions. Three of these regions can be directly observed and three cannot.
Earth's interior is composed of a thick, semi-solid mantle, which surrounds a smaller, two-part core. The inner core is solid, and the outer core is liquid. Above the mantle lies the thin crust, which makes up the continents and the sea floor. Above the crust is the hydrosphere, which contains oceans, rivers, and lakes. The atmosphere lies above Earth's surface, and at much higher altitudes, a protective tear-shaped layer known as the magnetosphere surrounds Earth.
Because seismic P- and S- waves are created by different kinds of motion, they interact with Earth matter in different ways. Please sort each wave type according to the types of Earth matter it travels through.
Pressure (P) waves are able to travel through both solids and liquids. Shear (S) waves, however, are absorbed by liquids and cannot travel through them; they can only travel through solid matter. This difference has been used by scientists to help analyze the interior structure of Earth based on their observations of seismic waves from distant earthquakes. Further information about Earth's interior can be determined from the arrival times of the seismic waves. The speed of each type of wave depends on the density and physical state of the matter through which it is traveling. Consequently, by measuring the time it takes for waves to move from the site of an earthquake to one or more monitoring stations on Earth's surface, geologists can infer the density of matter in Earth's interior.
By sensing the different types of seismic waves from earthquakes, it is possible to create a model of Earth's interior that satisfies scientific observations. Scientists station seismographs all around Earth to record earthquakes. By analyzing the data, scientists can determine which stations detect which kinds of waves from a particular earthquake. In the following figure, an earthquake on one side of Earth has produced longitudinal pressure waves (P-waves) and perpendicular shear waves (S-waves). The P-waves can travel through liquid, but the S-waves cannot. Given the interior structure depicted in the figure, label the types of waves that would be detected by stations at the four different positions.
When an earthquake occurs somewhere on Earth, P-waves travel through liquid and solid regions of Earth's interior and can be detected by seismographs that are nearly on the opposite side of the world. S-waves, however, are absorbed by the liquid outer core. This localized absorption produces a broad zone on the opposite side of Earth where no S-waves are detected. The size of this zone, along with the different arrival times of the seismic waves that are detected around the world, enable scientists to infer the compositions, densities, and temperatures present in Earth's interior.
o understand how Earth's interior structure was formed, we need to go back in time to its formation during the birth of the solar system. Astronomers believe that when Earth and the other terrestrial planets formed, a process called differentiation occurred. Rank the steps of the differentiation process in order from the initial stage to the final stage.
Earth started out as a self-gravitating concentration of rocky "planetesimals." Through the energy released by gravitational contraction, internal radioactivity, and further bombardment by interplanetary debris, the entire Earth likely melted and remained molten, or at least semisolid, for about a billion years. During this time, the relatively dense metals sank towards the center and the less dense silicates and other rocks floated towards the surface. This process of differentiation ended when the various layers re-solidified, thus forming the dense metal core, intermediate-density rocky mantle, and low-density rocky crust. The liquid outer core has yet to cool enough to solidify.
Chapters 8-10 (The Moon, Mercury, Venus, and Mars)
Which statement about the rotations of the Moon and Mercury is TRUE?
Mercury is in the 3:2 synch with the Sun, with the same side Sunward at perihelion.
On Mercury, three days exactly equal two years.
Our Moon is in a 1:1 synch with the Earth, keeping the same side toward us.
On the Moon, each "day" lasts about 15 earth days of constant sunlight.
The rate of cratering:
shows that most interplanetary debris was swept up soon after the formation of the solar system.
What two properties of Mercury imply that it is differentiated?
Its large average density and its magnetic field
What are the major factors that rule out the co-formation theory for the Moon-Earth system?
Each body has a different density and a different chemical composition.
In contrast with Earth, the Moon and Mercury undergo extremes in temperature. Why?
The extreme temperature variations of Mercury and the Moon are partly due to their lack of an atmosphere. An atmosphere helps a planet to retain heat at night; without one, the surface cools very rapidly. Both bodies also have slow rotation rates (very slow in Mercury), which create long days and nights. The Sun is up for a long period, allowing the rock to heat up. With an equally long night, there is ample time to cool down to a low temperature. By contrast, Earth spins rapidly and has less time to heat up to high temperatures or cool down to low temperatures.
The Moon has two distinct types of terrain: the maria and the highlands
The maria and highlands have distinctive appearances. The maria are dark and smooth, while the highlands are light-colored and rough
The Moon's maria and highlands can be described by the characteristics present in each
The maria are relatively dark-colored, smooth regions on the surface of the Moon. They were formed when molten lava flowed out of the crust and pooled in low-lying regions. The highlands, in contrast, are composed of relatively light-colored, rough terrain, which is elevated several kilometers above the maria.
The relative number of craters found in the maria and the highlands greatly differs. In addition, we have inferred that the maria formed from molten lava welling up from the Moon's mantle.
Craters occur when any meteoroids impact the surface, leaving depressions and reshaping the surface. The relative abundance of craters on the maria and the highlands give astronomers an indication of the relative ages of these lunar regions. The maria are more lightly cratered and are thus younger than the more heavily cratered highlands. The largest of the meteoroid impacts were so violent that they formed cracks in the crust and molten lava from the mantle welled up through these cracks and filled these large basins. This molten lava then solidified as it cooled, forming the maria. As time passes, the smooth surface of the maria is becoming slightly more cratered as well.
Compare the magnitude of the Sun's gravitational force on Mercury at locations A, B, and C
Mercury's near side, facing the Sun, is closer than the far side by approximately 2400 kilometers. The near side experiences a stronger gravitational attraction than the far side. This variation in one body's gravitational force from place to place across another body is called a tidal force. Because of Mercury's close proximity to the Sun it experiences a strong tidal force similar to the strong tidal force exerted by Earth on the Moon. This significant tidal force results in a slight deformation, or tidal bulge, of Mercury in the direction of the Sun.
In the mid-nineteenth century, astronomers thought that Mercury should be tidally locked to the Sun, meaning it would rotate once for every revolution around the Sun. This scenario would be similar to how the Moon is tidally locked in its orbit around Earth. However in the 1960s, astronomers determined that Mercury is not tidally locked to the Sun. The large eccentricity (exaggerated in the figure) of Mercury's orbit causes large variations in its orbital speed, which prevents tidal locking. Rank the following orbital locations from the fastest orbital speed to the slowest.
Kepler's second law of planetary motion states that a planet's orbital speed varies at different points along its orbit. When Mercury is closest to the Sun in its orbit (perihelion), Mercury's orbital speed is fastest. When Mercury is farthest from the Sun in its orbit (aphelion), Mercury's orbital speed is slowest.
An orbiting body with a tidal bulge, such as Mercury, will try to settle into a synchronous orbit with its partner (in this case, the Sun). However, due to the large eccentricity of Mercury's orbit, the orbital speed at perihelion is very different from the speed at aphelion, making it impossible for Mercury and the Sun to lock in a synchronous orbit. Even though Mercury's orbital speed changes as it travels around the Sun. Mercury's rotation rate and orbital period will synchronize into a simple spin-orbit resonance. Will it synchronize at perihelion or aphelion?
The tidal forces exerted on Mercury by the Sun are the greatest at the perihelion position, thus the influence on the rotation rate is also the greatest. Mercury's spin rate and orbital rate are essentially synchronized at perihelion, resulting in a spin-orbit resonance of 3:2. This resonance means that for every one complete orbit around the Sun, Mercury completes 1.5 rotations. Thus, Mercury's tidal bulge is always aligned toward the Sun at the perihelion position. Use the following interactive figure to see this and other resonances.
What are the three theories for the formation of the Moon?
The three leading theories for the formation of the Moon are the coformation theory, the capture theory, and the impact theory. The coformation theory states that Earth and the Moon formed at about the same time out of the same pre-planetary matter. The capture theory states that the Moon formed far from Earth and later became gravitationally bound by Earth after a close encounter. According to the impact theory, a glancing collision between a large, Mars-sized object and a youthful, molten Earth led to the formation of the Moon.
A theory is a framework of ideas and assumptions used to explain some set of observations and to make predictions about the real world. Each of the three theories for the formation of the Moon lead to different predictions about evidence that we should find. Which of the following predictions should be true if each theory is correct?
The theories of the Moon's formation make different predictions:
•The Moon and Earth should have very similar compositions.
•The Moon and Earth should have similar densities.
•The Moon and Earth should have completely different compositions.
•Mathematical models should predict that the capture of a Moon-sized satellite would be likely in Earth's early history.
•Earth and the Moon should have similar mantles and dissimilar cores.
•Computer simulations should predict that a collision between Earth and a Mars-sized object would produce a Moon-sized satellite with a stable orbit.
If any of the theories are true, their predictions should bear out in the actual evidence.
To be effective, a scientific theory must be continually tested. If observations and experiments favor it, a theory can be further developed and refined. If they do not, the theory must be reformulated or rejected. Comparing what you know about the predictions of each Moon formation theory, determine which of the following observations and experiments have been verified.
Several observations and experiments have helped determine the validity of the theories of Moon formation:
•Earth has a large iron core, but the Moon does not.
•The mantles of Earth and the Moon have similar compositions.
•Computer simulations predict that a collision between Earth and a Mars-sized object would produce a Moon-sized satellite with a stable orbit.
This evidence supports neither the coformation theory nor the capture theory. The Moon and Earth are too dissimilar in density and core composition to have formed together out of the same pre-planetary matter, ruling out the coformation theory. The similar composition of the mantles of the Moon and Earth make it unlikely that the Moon and Earth formed entirely independently. In addition, mathematical models suggest it is highly unlikely for Earth to have captured an object the size of the Moon. Thus the evidence rules out the capture theory. However, the evidence does support the impact theory, and scientists continue to develop and refine this theory.
Based on the evidence for the impact theory, what was the most probable order of events for the collision that led to the formation of the Moon?
According to the impact theory, a glancing collision between a Mars-sized object and Earth led to the formation of the Moon. The iron core of Earth had formed before this collision, leading to the similarity between the composition of the Moon and Earth's mantle. After the collision, any iron core of the Mars-sized object would have been left behind on Earth and eventually merged with Earth's core. The Moon then formed out of the debris thrown into space by the collision.
Volcanic activity on Venus is thought to be:
less frequent, but more violent than volcanic activity on Earth.
Venus lacks a planetary magnetic field because
it rotates very slowly.
If Mars' atmosphere is mostly carbon dioxide, why isn't it as hot as Venus?
Venus is hot because of the greenhouse effect. Due to Venus' atmosphere being extremely dense and far from the surface more greenhouse gases are able to accumilate between the atmosphere, intensifying the greenhouse effect. Its thick carbon dioxide blanket absorbs nearly 99 percent of all the infrared adiation released from the surface of Venus. So the thick layers of atmosphere on Venus act as a pressure cooker with the greenhouse effect for the planet, making temperatures extremely high. Comparatively, Mars' atmosphere is much thinner than that of Earth's, let alone Venus'. Such a thin atmosphere makes the planet unable to withhold greenhouse gases that lead to the greenhouse effect, giving the planet additional heat, besides that from sunlight.
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?
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.
Which of the following Mars surface features provides dramatic evidence that volcanism has played a role in shaping the surface of Mars?
Olympus Mons is a very large shield volcano. You can also see numerous other volcanoes on Mars, including three large ones on the Tharsis bulge
When you zoom in on the section labeled "Southern Highlands," which geologic processes are most clearly evident?
The most obvious features of the southern highlands are the many impact craters, but a close examination shows that many of them have been "smoothed out," indicating erosion that has occurred over time.
Listed below are geographic features of the terrestrial worlds. In each case, identify the geological process (impact cratering, volcanism, erosion, or tectonics) most responsible for the feature described. Match the geographic feature to the appropriate geologic process.
Remember that the four processes are interrelated, so although one may be most important to a particular feature, others often also play a role. For example, some erosion has occurred on the volcanic island of Hawaii, there are impact craters on the slopes of Olympus Mons, and volcanism and tectonics almost always go hand-in-hand.
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.
Note that the pressure differences are quite extreme. Mercury has essentially no atmosphere and no pressure. Earth's atmospheric pressure is more than 100 times that of Mars, and Venus's atmospheric pressure is about 90 times that of Earth.
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. (Not to scale.)
Note that this ranking is the same as the pressure ranking from Part A. This should not be surprising, because more atmospheric gas generally means more pressure (though the strength of gravity at a planet's surface also plays a role in determining the pressure).
Listed following are characteristics of the atmospheres of Venus, Earth, and Mars. Match each atmospheric characteristic to the appropriate planet.
Be sure to recognize that Venus has very little wind because of its slow rotation rate. Venus suffered a runaway greenhouse effect because of its distance from the Sun; If Earth were placed at the same distance, our planet would suffer the same fate. Earth has an ultraviolet-absorbing stratosphere because of the oxygen in the atmosphere, which at high altitudes forms molecules of ultraviolet-absorbing ozone.