An understanding of how Earth’s oceans were formed must begin with an examination of how our solar system developed. Scientists believe our solar system began forming as a huge cloud of dust that collapsed to form a sun surrounded by a flat disk of particles rotating around it, This disk-the solar nebula, as it is called-was denser in the center than it was in its outer reaches. It was also hotter in the center-perhaps as hot as 1,200 degrees Celsius, in the region where Earth now finds itself. And because the central part of the disk was hotter, it was also rockier. Only rocky grains,could survive the intense heat; ice, including water ice, would have been vaporized.
1.The word “intense’ in the passage is closest in meaning to
A.central
B.extreme
C.destructive
D.constant
2.According to paragraph 1, which of the following best describes the solar nebula?
A.It was a collection of dust particles replaced by a rotating sun.
B.It was a disk-shaped region containing rocky grains rotating around a central sun.
C.It was a disk-shaped region of water vapor made from ice vaporized by heat from a central sun.
D.It was a cloud of dust grains, which collected in the hotter outer reaches of the cloud.
As the dust grains were falling down into the solar disk,they began to collide and stick together, especially once they were in the disk. ▉Clumps formed, then bigger clumps, until soon the space that is now occupied by the inner planets (Mercury, Venus, Earth, and Mars) was littered with ten billion rocks the size of asteroids, about five or ten miles across. These rocks were large enough to attract one another gravitationally. As they orbited the Sun in the same direction, they forced each other into higher velocities, but whenever they collided, they slowed one another down .▉Scientists have calculated that the net effect of these competing influences would be to keep the relative yelocities of the rocks low, and thus the collisions between them gentle一gentle enough that two colliding rocks would often stick together rather than fly apart. ▉Within a million years after the Sun first formed.most of the dust in the inner solar system had settled onto 30 or so planet “embryos” (planets in their early.undeveloped stage of formation) the size of Mercury.▉
These embryos rotated around the Sun, but they did not stay on safe, circular orbital paths for long. The gravitational attraction among them soon forced the issue. The embryos’ orbits became more elliptical (egg shaped), and their paths began to cross-and so they began to collide, not gently, but at speeds of tens of thousands of miles per hour. Only the embryos that started out somewhat larger than the rest could survive such impacts, and they proceeded to grow even larger by absorbing the others. Within 10 to 100 million years, this process had produced the four inner planets.
3.Paragraph 3 supports which of the following statements about the smaller embryos?
A.They remained on circular orbital paths longer than the larger embryos did.
B.They were destroyed in collisions after their orbital paths had become elliptical.
C.They moved at higher speeds than the larger embryos did.
D.They escaped collisions because of their smaller size.
4.Paragraph 3 implies that which of the following caused the planet embryos to lose their circular orbits?
A.The Sun’s gravity
B.The increased speed of the embryos’ rotation around the Sun
C.The gravitational pull of the embryos on each other
D.The gentle collisions among the embryos
This picture of Earth has, in just the past two or three decades, completely changed the traditional view of the planet’s early history, and in particular of how it developed oceans. As long as it was thought that Earth condensed from a giant gaseous planet embryo, or that it grew gently by sweeping up small particles that happened to be in its path, it was also assumed that the early Earth was cold. Only gradually did it heat up, in this view, as uranium and other radioactive elements embedded in its rock decayed and released heat;only gradually did the heat drive water vapor, which had attached itself to rocky minerals in the solar nebula, out of Earth’s interior. Erupting in great clouds from volcanoes-a process called “out gassing”一the water vapor condensed and rained out of the atmosphere. Gradually, according to this idea, over hundreds of millions or even billions of years, the oceans were created.
5.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A.In this view, radioactive elements became embedded in rocky minerals in the solar nebula,causing Earth to heat up gradually.
B.In this view, water vapor gradually became embedded in rocky minerals, which were heated up when they came in contact with radioactive elements.
C.In this view, the heat from water vapor gradually caused the radioactive elements inside Earth to decay.
D.In this view, Earth heated up gradually, as radioactive elements decayed and released heat that drove water vapor out of Earth’s interior.
6.According to paragraph 4, what was one reason why some scientists formerly believed that early Earth was low in temperature?
A.They thought that Earth developed from a gaseous planet embryo.
B.They assumed that early Earth lacked radioactive elements.
C.They believed that Earth’s interior had relatively little water vapor.
D.They thought that Earth could not have been formed from small particles.
7.According to paragraph 4, all of the following were steps in the traditional view of how Earth’s oceans formed EXCEPT:
A.Out gassing brought water vapor from Earth’s interior to its exterior.
B.Water vapor became attached to rocky minerals while in the solar nebula.
C.Water vapor condensed into rain in Earth’s atmosphere.
D.Heat from volcanic eruptions helped warm early Earth’s interior.
The traditional view notwithstanding, it probably did not happen that way. For one thing, the available evidence suggests that over Earth’s entire 4.6-billion-year history there has not been enough volcanic activity to produce an ocean. But in retrospect the whole volcanic“out gassing” scenario rested on a misconception. it is simply not possible for a planet to grow quietly.coolly to maturity. Once the Earth embryo was the size of Mercury, any incoming rock, be it the size of an asteroid or a small planet, would be accelerated to such a terrific velocity by Earth’s gravity that on impact it would shatter and melt or even vaporize. Besides releasing a great deal of heat, the explosion would immediately set free any water trapped in the rock. If Earth formed from colliding embryos, it formed not cold but hot, and, assuming there was water trapped in the rock, it formed wet, right from the beginning.
8.Why does the author point out that “lt is simply not possible for a planet to grow quietly, coolly to maturity”?
A.To imply that Earth’s growth probably was speeded by the heat produced by volcanic activity
B.To give a reason why Earth’s oceans must have formed gradually over billions of years
C.To introduce an idea that helps explain why the traditional view of ocean formation is probably not correct
D.To explain why there has not been enough volcanic activity over Earth’s history to produce an ocean
9.Look at the four squares [▊] that indicate where the following sentence could be added to the passage.Where would the sentence best fit?
Thus they experienced situations that had opposite effects on their orbital velocities.
10.Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Knowledge of how Earth and the inner planets were formed is needed to understand how the oceans may have formed.
A.Our solar system originated from a cloud of dust that collapsed into a rotating disk of particles, which clumped together into planet embryos that orbited the Sun.
B.As the solar nebula rotated, the rocky particles were forced outward, resulting in a solar nebula of uniform density and temperature.
C.Radioactive materials found in the original dust cloud heated up the planet embryos, which allowed them to stick together and form the four inner planets.
D.Earth’s oceans formed from water vapor that was released during the radioactive decay of elements embedded in Earth’s interior.
E.Scientists once thought that heat from Earth’s interior forced water vapor into the atmosphere where it condensed into liquid water that accumulated over time into the oceans.
F.Because large impacts release heat and water and because Earth has never had enough volcanic activity to produce enough water vapor to fill oceans, it seems likely that Earth was always hot and wet.
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