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Astronomy Chapter 8

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The age of the solar system can be established by radioactive dating of…
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The oldest meteorites
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In essence, the nebular theory holds that:
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our solar system formed from the collapse of an interstellar cloud of gas and dust
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Which of the following types of material can condense into what we call ice at low temperatures?
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Hydrogen compounds
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What do we mean by the frost line when we discuss the formation of planets in the solar nebula?
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It is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense.
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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?
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You’ll have 0.25 kilogram of the radioactive substance remaining.
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What is the leading hypothesis for the origin of the Moon?
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It formed from the material ejected from Earth in a giant impact.
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According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size?
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It got hotter, its rate of rotation increased, and it flattened into a disk.
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Our solar system was created by the gravitational collapse of the __________.
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solar nebula
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__________ allows us to determine the age of a solid rock.
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Radiometric dating
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Ice can form from a gas through the process of:
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Condensation
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Mars was formed by the __________ of smaller objects.
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accretion
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Our Moon was most likely formed by a collision between Earth and a Mars-sized __________.
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planetesimal
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The first few hundred million years of the solar system’s history were the time of the __________, during which Earth suffered many large impacts.
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heavy bombardment
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The era of planet formation ended when the remaining hydrogen and helium gas of the solar nebula was swept into interstellar space by the __________.
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solar wind
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Hydrogen compounds in the solar system can condense into ices only beyond the __________.
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frost line
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What law explains why cloud spins faster as it shrinks in size?
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the law of conservation of angular momentum
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What law explains why the center of the cloud becomes so much hotter as the cloud shrinks in size?
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the law of conservation of energy
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Significance of the meteorite?
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The shiny metal flakes embedded in rock are just what we expect if condensation really occurred as the nebular theory predicts.
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Where did the elements heavier than hydrogen and helium come from?
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They were produced inside stars.
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What percentage of the mass of the solar nebula consisted of elements other than hydrogen and helium?
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2 percent
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True or false: We have direct evidence from ALMA that supports nebular theory.
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True
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True or false: Nebular theory supports that other solar systems that formed in the same way should have 8 planets.
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False
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Why did the solar nebula heat up as it collapsed?
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As the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy.
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Why did the solar nebula flatten into a disk?
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It flattened as a natural consequence of collisions between particles in the spinning nebula, changing random motions into more orderly ones.
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What happened during the accretion phase of the early solar system?
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Particles grew by colliding and sticking together.
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According to our theory of solar system formation, why do all the planets orbit the Sun in the same direction and in nearly the same plane?
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The laws of conservation of energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk.
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Which of the following lists the ingredients of the solar nebula from highest to lowest percentage of mass of the nebula?
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light gases (H, He), hydrogen compounds (H2O, CH4, NH3), rocks, metals
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What percentage of the solar nebula’s mass consisted of hydrogen and helium gases?
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98 percent
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What percentage of the solar nebula’s mass consisted of rocky material?
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0.4 percent
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What kind of material in the solar nebula could remain solid at temperatures as high as 1,500 K, such as existed in the inner regions of the nebula?
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Metals
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What was the frost line of the solar system?
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The distance from the Sun where temperatures were low enough for hydrogen compounds to condense into ices, between the present-day orbits of Mars and Jupiter
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Why are the inner planets made of denser materials than the outer planets?
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In the inner part of the nebula only metals and rocks were able to condense because of the high temperatures, whereas hydrogen compounds, although more abundant, were only able to condense in the cooler outer regions.
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Which of the following is the origin of almost all the large moons around the jovian planets?
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They were formed by condensation and accretion in a disk of gas around the planet.
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What is the most likely reason that there are no giant planets beyond Neptune?
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By the time planetesimals grew to a large enough mass to hold onto an atmosphere, the solar nebula had been blown away.
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Observations of young stars (as well as theory) tell us that when the Sun was young the solar wind…
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was stronger than it is today.
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At first, the Sun’s present-day rotation seems to contradict the prediction of the nebular theory because…
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the theory predicts that the Sun should have been rotating fast when it formed, but the actual rotation is fairly slow.
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According to our theory of solar system formation, why does the Sun rotate slowly today?
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The Sun once rotated much faster, but it transferred angular momentum to charged particles caught in its magnetic field and then blew the particles away with its strong solar wind.
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Which of the following are relatively unchanged fragments from the early period of planet building in the solar system? asteroids the moons of Mars Oort cloud comets Kuiper belt comets all of the above
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All of the above
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According to the nebular theory, what are asteroids and comets?
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They are leftover planetesimals that never accreted into planets.
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According to the nebular theory, how did the Kuiper belt form?
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It is made of planetesimals that formed beyond Neptune’s orbit and never accreted to form a planet.
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According to our theory of solar system formation, why do we find some exceptions to the general rules and patterns of the planets?
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Most of the exceptions are the result of giant impacts.
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Based on our current theory of Earth’s formation, the water we drink comes from…
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comets that impacted Earth.
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The heavy bombardment phase of the solar system lasted…
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several hundreds of millions of years.
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Which of the following is not evidence supporting the giant impact theory for the formation of the Moon?
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Scientists have found several meteorites that appear to be the remains of the object that caused the giant impact.
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Which of the following puzzles in the solar system cannot be explained by a giant impact event?
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The orbit of Triton in the opposite direction to Neptune’s rotation
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The nebular theory of the formation of the solar system successfully predicts all but one of the following. Which one does the theory not predict?
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The equal number of terrestrial and jovian planets
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True or false: All the planets in the solar system rotate in the same direction as they orbit the Sun.
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False
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As viewed from above Earth’s North Pole, all of the planets orbit the Sun in the same (counterclockwise) direction.
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True
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True or false: The more massive planets in the solar system tend to be less dense than the lower mass planets.
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True
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True or false: Within the frost line, planetesimals were composed entirely of rock and outside the frost line planetesimals were composed entirely of ice.
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False
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True or false: Impacts were extremely common in the young solar system but no longer occur today.
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False
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True or false: Earth’s atmosphere resulted from the impact of icy planetesimals that originated in the outer regions of the Solar System.
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True
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True or false: The Moon probably formed at the same time that Earth formed, rather like the formation of a double planet.
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False
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True or false: Some radioactive isotopes found in meteorites suggest that the solar system may have been formed shortly after a supernova occurred nearby.
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True
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True or false: Process of Science: We cannot test the nebular theory for the formation of the Solar System in a rigorous scientific way because the Sun and planets formed in the distant past.
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False
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The age of our solar system is approximately…
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4.6 billion years
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What do meteorites reveal about the solar system?
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They reveal that the age of the solar system is approximately 4.6 billion years.
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Suppose you find a rock that contains some potassium-40 (half-life of 1.3 billion years). You measure the amount and determine that there are 5 grams of potassium-40 in the rock. By measuring the amount of its decay product (argon-40) present in the rock, you realize that there must have been 40 grams of potassium-40 when the rock solidified. How old is the rock?
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3.9 billion years
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True or false: Based on our theory of how our own solar system formed, we would expect that other solar systems would be quite common.
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True