【正文】 lted more easily ? was more radioactive ? was more plentiful Paragraph 3: As heavy materials headed for the center of Earth, lighter silicates (such as the mineral quartz) drifted upward. The denser silicates formed Earth39。s interior. These lighter materials, such as the rocks we call granites, formed a layer of continental crust about 35 kilometers thick. Relative to Earth as a whole, this is as thin as an eggshell. Seafloor crust is even thinner, at about 7 kilometers。s continental crust ? has changed significantly in position over time ? was as thick as Earth39。s interior to the surface. So we can imagine the surface of the early Earth as a massive volcanic field. And we can judge pretty well what gases bubbled up to that surface by analyzing the mixture of gases emitted by volcanoes. These include hydrogen, helium, methane, water vapor, nitrogen, ammonia, and hydrogen sulfide. Other materials, including large amounts of water vapor, were brought in by etary bombardments. Much of the hydrogen and helium escaped。s surface. ? It lacked water vapor. Paragraph 3: As heavy materials headed for the center of Earth, lighter silicates (such as the mineral quartz) drifted upward. The denser silicates formed Earth39。s interior. ■These lighter materials, such as the rocks we call granites, formed a layer of continental crust about 35 kilometers thick. ■Relative to Earth as a whole, this is as thin as an eggshell. ■Seafloor crust is even thinner, at about 7 kilometers。s lack of an atmosphere explains why it was bombarded with much more frequency and violence than other plaesimals. ? Continued bombardments and internal pressures made the growing Earth hotter, causing its interior to melt and the heavier elements to sink and form Earth39。s lack of an atmosphere explains why it was bombarded with much more frequency and violence than other plaesimals. ? Continued bombardments and internal pressures made the growing Earth hotter, causing its interior to melt and the heavier elements to sink and form Earth39。 however, there were not yet efficient means by which to produce mechanical energy or to power machinery. This was to occur with progress in the development of the steam engine. In the late 1700s James Watt designed an efficient and mercially viable steam engine that was soon applied to a variety of industrial uses as it became cheaper to use. The engine helped solve the problem of draining coal mines of groundwater and increased the production of coal needed to powe。s interior rose and formed the mantle, a denser layer of silicates around the core, and the crust, a thinner layer of silicates at Earth39。s interior rose and formed the mantle, a denser layer of silicates around the core, and the crust, a thinner layer of silicates at Earth39。s core. Much of the early continental crust has remained on Earth39。s surface, the lightest silicates rose to Earth39。s first stable atmosphere. 11. The word emitted in the passage is closest in meaning to ? Released ? Consumed ? Contained ? Heated 12. What can be inferred from paragraph 4 about Earth39。s size ? caused the temperatures of Earth39。s core. Much of the early continental crust has remained on Earth39。s surface, the lightest silicates rose to Earth39。s core was nickel ? What internal pressures caused Earth to heat up as it grew in size ? What caused Earth39。 but once Earth was fully formed, it was large enough for its gravitational field to hold most of the remaining gases, and these formed Earth39。 thus, even continental crust reaches only about 1/200th of the way to Earth39。s mantle, a region almost 3,000 kilometers thick between the core and the crust. With the help of bombardment by ets, whose many impacts scarred and heated Earth39。 those of others were on or a part of the body surface. One animal, Opabinia, had five eyes: two lateral pairs and a single medial eye。 those of others were on or a part of the body surface. One animal, Opabinia, had five eyes: two lateral pairs and a single medial eye。 they were found on a mountainside in British Columbia in a deposit known as the Burgess Shale. The Burgess Shale fossils are extraordinarily important because among them are remains of softbodied creatures, many of them lacking shells and other hard parts that fossilize easily. Consequently, their preservation is little short of miraculous (as are the delicate methods used to reconstruct threedimensional structure from these flattened fossils), and they are one of the few known repositories of early softbodied animals. Not all of the Burgess animals had eyes. However, some did. (Gross features location, size, and hemispheric shape are responsible for the designation of some structures as eyes). The reconstructed eyes of these Burgess animals look superficially like eyes of some living crustaceans, particularly those of shrimp and crabs whose eyes are mounted on stalks that improve the range of vision by raising the eyes above the surface of the head. The eyes of some Burgess anisms sat on stalks。 they were found on a mountainside in British Columbia in a deposit known as the Burgess Shale. The Burgess Shale fossils are extraordinarily important because among them are remains of softbodied creatures, many of them lacking shells and other hard parts that fossilize easily. Consequently, their preservation is little short of miraculous (as are the delicate methods used to reconstruct threedimensional structure from these flattened fossils), and they are one of the few known repositories of early softbodied animals. 7. The phrase little short of miraculous is closest in meaning ? To very highly valued ? Amazing because almost impossible ? Causing controversy ? Almost but not quite plete 8. According to paragraph 4, all of the following are true of the Bur