Astronomy Homework 5

[ Question] In general, what kind of planet would you expect to have the thickest lithosphere? [Options] [A] A Small Planet [B] A Large Planet [C] A Planet far from the sun

[Answer] [A] A Small Planet

[ Question] Which of a planet's fundamental properties has the greatest effect on its level of volcanic and tectonic activity? [Options] [A] Size [B] Distance from the sun [C] Rotation rate

[Answer] [A] Size

[Question] What's the leading theory for the origin of the Moon? [Options] [A] It formed along with Earth. [B] It formed from the material ejected from Earth in a giant impact. [C] It split out of a rapidly rotating Earth.

[Answer] [B] It formed from the material ejected from Earth in a giant impact.

[Question] Which of the following did not occur during the collapse of the solar nebula? [Options] [A] spinning faster [B] concentrating denser materials nearer the Sun [C] heating up

[Answer] [B] concentrating denser materials nearer the Sun

[Question] What is the longest-lasting internal heat source responsible for geological activity? [Options] [A] accretion [B] radioactive decay [C] sunlight

[Answer] [B] radioactive decay

[Question] According to modern scientific dating techniques, approximately how old is the solar system? [Options] [A] 14 billion years [B] 4.6 million years [C] 4.5 billion years [D] 10,000 years

[Answer] [C] 4.5 billion years

[ Question] What do we conclude if a planet has few impact craters of any size? [Options] [A] The planet was never bombarded by asteroids or comets. [B] Its atmosphere stopped impactors of all sizes. [C] Other geological processes have wiped out craters.

[Answer] [C] Other geological processes have wiped out craters.

[ Question] Based on its surface features, the most important event on Venus in the past billion years or so was _______. [Options] [A] the impact of an unusually large asteroid that left a deep scar on one side of the planet [B] the onset of mantle convection, which caused Venus's lithosphere to split into plates like those on Earth [C] the eruption of a giant volcano that formed one of Venus's "continents" [D] a global "repaving" that erased essentially all the surface features that had existed earlier

[Answer] [D] a global "repaving" that erased essentially all the surface features that had existed earlier

[ Question] Which of the following best describes the lunar maria? [Options] [A] mountainous regions on the Moon [B] frozen oceans of liquid water on the Moon [C] densely cratered regions on the Moon [D] relatively smooth, flat plains on the Moon

[Answer] [D] relatively smooth, flat plains on the Moon

[ Question] Based on Planet Z's size, orbital distance, and rotation rate, which of the following properties is it likely to have? [Options] - a surface crowded with impact craters - active tectonics - seasons - strong winds and violent storms - active volcanoes - polar ice caps - erosion due to liquid water - an atmosphere produced by outgassing

[Answer] - active tectonics - active volcanoes - an atmosphere produced by outgassing [Explanation] Continue on to explore why the planet has these characteristics.

[Question] Match the words in the left-hand column to the appropriate blanks in the sentences in the right-hand column. Use each word only once. [1.] Our solar system was created by the gravitational collapse of the ________. [2.] Our Moon was most likely formed by a collision between Earth and a Mars-sized ________. [3.] The first few hundred million years of the solar system's history were the time of the ________, during which Earth suffered many large impacts. [4.] Mars was formed by the ________ of smaller objects. [5.] The era of planet formation ended when the remaining hydrogen and helium gas of the solar nebula was swept into interstellar space by the ________. [6.] Ice can form from a gas through the process of ________. [7.] Hydrogen compounds in the solar system can condense into ices only beyond the ________. [8.] ________ allows us to determine the age of a solid rock. [Options] - solar wind - frost line - planetesimal - solar nebula - condensation - heavy bombardment - Radiometric dating - Accretion

[Answer] [1.] solar nebula. [2.] planetesimal. [3.] heavy bombardment [4.] accretion [5.] solar wind. [6.] condensation. [7.] frost line. [8.] Radiometric dating

[ Question] Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once. [Options] - Fault - Seafloor Spreading - Subduction - Sedimentary Rock - Seafloor Crust - Hot Spot - Continental Crust [1.] The slowly increasing distance between South America and Africa is due to ________. [2.] Old Faithful Geyser at Yellowstone National Park in the United States acquires its energy from a ________. [3.] Layered ________ exposed by erosion can be seen when looking at the Grand Canyon in the United States. [4.] Australia is composed of relatively old and thick ________. [5.] The extremely deep ocean Marianas Trench is a result of ________. [6.] ________ found in the Atlantic Ocean between North America and Europe is composed of dense and relatively young rock. [7.] The earthquakes that occur in Southern California generally occur above a ________.

[Answer] [1] seafloor spreading [2] hot spot [3] sedimentary rock [4] continental crust [5] subduction [6] Seafloor crust [7] fault

[Question] You are dating rocks by their proportions of parent isotope potassium -40 (half-life 1.25 billion years) and daughter isotope argon -40. [A] Find the age for a rock that contains equal amounts of potassium -40 and argon -40. Express your answer using three significant figures. [B] Find the age for a rock that contains three times as much argon -40 as potassium -40. Express your answer using three significant figures.

[Answer] [A] 1.25 [B] 2.5

[Question] What are the basic requirements for a terrestrial world to have a global magnetic field? [Options] [A] a core that has a molten layer and a mantle that has convection [B] a metal core, a rocky mantle, and sufficiently rapid rotation [C] a core layer of molten, convecting material and sufficiently rapid rotation [D] a metal core and rapid rotation

[Answer] [C] a core layer of molten, convecting material and sufficiently rapid rotation

[Question] Suppose you start with 1 kilogram of a radioactive substance that has a half-life of 10 years. Which of the following statements will be true after 20 years pass? [Options] [A] All the material will have completely decayed. [B] You'll have 0.5 kilogram of the radioactive substance remaining. [C] You'll have 0.75 kilogram of the radioactive substance remaining. [D] You'll have 0.25 kilogram of the radioactive substance remaining.

[Answer] [D] You'll have 0.25 kilogram of the radioactive substance remaining.

[Question] As you've learned from Part B, hydrogen and helium gas never condense under conditions found in the solar nebula. The remaining three categories of material in the solar nebula are shown again here. Rank these materials from left to right based on the distance from the Sun at which they could condense into a solid in the solar nebula, from farthest to closest. [Options] - Rock - Metals - Hydrogen Compounds

[Answer] [Farthest] - Hydrogen Compounds - Rock - Metals [Closest] [Explanation] These condensation regions explain the makeup of objects at different distances from the Sun. In the inner regions of the solar nebula, where temperatures were high, only metal and rock could condense, which is why the inner planets ended up being made of metal and rock. Farther out, hydrogen compounds could condense into ices, which is why comets and outer solar system moons contain large amounts of ice. And because hydrogen compounds are more abundant than metal or rock, some of the solid objects in the outer solar system grew so large that their gravity could pull in hydrogen and helium gas, which explains how the jovian planets formed.

[Question] 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. [Options] - Venus - Mars - Earth - Mercury

[Answer] [Fastest Cooling] - Mercury - Mars - Venus - Earth [Slowest Cooling] [Explanation] Smaller planets cool faster than larger planets for the same reason that smaller hot potatoes cool faster than larger hot potatoes: An object's total heat content depends on its volume, while its rate of heat loss depends on its surface area. Smaller objects have greater ratios of surface area to volume (the surface area-to-volume ratio) and therefore cool faster. Note that the differing cooling rates explain why the smallest planet, Mercury, has lost most of its interior heat by now, while the largest terrestrial planets — Venus and Earth — still are quite hot inside.

[Question] The materials that made up the solar nebula can be categorized into the four general types as follows. Rank these materials from left to right based on their abundance in the solar nebula, from highest to lowest. [Options] - Rock - Hydrogen and Helium Gas - Metals - Hydrogen Compounds

[Answer] [Highest Abundance] - Hydrogen and Helium Gas - Hydrogen Compounds - Rock - Metals [Lowest Abundance] [Explanation] Knowing this ranking order is useful, but even more important is to recognize the vast differences in abundance: Hydrogen and helium gas constituted about 98 percent of the mass in the solar nebula. Most of the rest was hydrogen compounds, which were nearly three times as abundant as rock and metal combined.

[Question] The materials that made up the solar nebula can be categorized into these four general types. Rank these materials from left to right based on the temperature at which each would condense into a solid, from highest to lowest. Note: For a substance that does not condense at all, rank it as very low temperature. [Options] - Rock - Hydrogen and Helium Gas - Metals - Hydrogen Compounds

[Answer] [Highest Temperature] - Metals - Rock - Hydrogen Compounds - Hydrogen and Helium Gas [Lowest Temperature] [Explanation] In fact, hydrogen and helium gas never condense into solid form under the conditions that exist in interstellar clouds such as the solar nebula. Continue on to Part C to see how the condensation temperatures of the other materials explain why different materials condensed in different regions of the young solar system.

[Question] 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. [Options] [A] Mercury [B] Earth [C] Mars

[Answer] [Longest Time] - Earth - Mars - Mercury [Shortest Time] [Explanation] Earth still has a great deal of tectonic activity today, Mars has much less ongoing tectonic activity, and Mercury probably has very little or no ongoing tectonic activity. Note that we can trace these facts directly back to the cooling rates from Part A: Tectonic activity requires interior heat, so planets that cool faster lose their tectonic activity in a shorter time.

[ Question] [Part B] 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? [Options] [A] has a large size for a terrestrial planet. [B] has a slow rotation rate. [C] closely orbits its star. [D] lacks axis tilt. ______________________________ [Part C] 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? [Options] [A] a larger axis tilt [B] a greater distance from its star [C] a larger size [D] a smaller size ______________________________ [Part D] 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] a larger axis tilt [B] a greater distance from its star [C] a faster rotation rate [D] a smaller size ______________________________ [Part E] 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] a larger axis tilt [B] a faster rotation rate [C] a greater distance from its star [D] a smaller size

[Answer] [Part B] [A] has a large size for a terrestrial planet. [Explanation] Large size means more internal heat. This internal heat drives active tectonics and volcanism, which is the source of outgassing. ______________________________ [Part C] [B] a greater distance from its star [Explanation] The planet is too hot for liquid water or ice, so moving it farther from its star would allow it to cool down. If it cooled enough—but not too much—it could have surface liquid water and ice caps. ______________________________ [Part D] [C] a faster rotation rate [Explanation] The basic requirements for strong winds and violent storms are an atmosphere and relatively rapid rotation. An atmosphere is necessary to have wind of any type, while rotation is necessary to create the forces (in particular, the Coriolis force) that tend to drive winds on a planet's surface. Storms will be even stronger if there is also evaporation of surface water. ______________________________ [Part E] [A] a larger axis tilt [Explanation] Seasons are caused primarily by axis tilt, so a planet without axis tilt is not expected to have seasons (unless it has a highly elliptical orbit).

[ Question] 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. [Options] - Earths grand canyon - Mar's Valles Marineris - Current location of Earth's continents - Mar's Olympus Mons - Smooth surfaces of the lunar maria - Old surface features of the lunar highlands - Mercury's Many Long, Tall Cliffs - Big Island of Hawaii

[Answer] [impact cratering] - Big Island of Hawaii - Smooth surfaces of the lunar maria - Mar's Olympus Mons [volcanism] - Old surface features of the lunar highlands [erosion] - Earths grand canyon [tectonics] - Current location of Earth's continents - Mar's Valles Marineris - Mercury's Many Long, Tall Cliffs [Explanation] 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.

[ Question] Typical motions of one plate relative to another are 1 centimeter per year. At this rate, how long would it take for two continents 3300 kilometers apart to collide? Express your answer using two significant figures.

[Answer] ...

[ Question] How many of the five terrestrial worlds have surfaces being constantly reshaped by plate tectonics? [Options] [A] One [B] Two [C] Three or more

[Answer] [A] One

[ Question] How many of the five terrestrial worlds are considered "geologically dead"? [Options] [A] None [B] Two [C] Four

[Answer] [B] Two

[ Question] On how many of the five terrestrial worlds has erosion been an important process? (Be sure that you explain why erosion is important on this many worlds and not more.) [Options] [A] One [B] Two [C] Three or more

[Answer] [B] Two