托福 Z托福 08 - Origin of the Solar System
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The orderly nature of our solar system leads most astronomers to conclude that the planets formed at essentially the same time and from the same primordial (original) material as the Sun. This material formed a vast cloud of dust and gases called a nebula. The nebular hypothesis suggests that all bodes of the solar system formed from an enormous nebular cloud consisting mostly of hydrogen and helium as well as a small percent of all the other heavier elements known to exist. The heavier substances in this frigid cloud of dust and gases consisted mostly of such elements as silicon, aluminum, iron, and calcium—the substances of today’s common rocky materials. Also prevalent were other familiar elements, including oxygen, carbon, and nitrogen.

Nearly five billion years ago, some external influence, such as a shock wave traveling from a catastrophic explosion (supernova), may have triggered the collapse of this huge cloud of gases and minute grains of heavier elements, causing the cloud to begin to slowly contract due to the gravitational interactions among its particles. As this slowly spiraling nebula contracted, it rotated faster and faster for the same reason ice-skaters do when they draw their arms toward their bodies. Eventually, the inward pull of gravity came into balance with the outward force caused by the rotational motion of the nebula. By this time the once vast cloud had assumed a flat disk shape with a large concentration of material at its center, called the protosun (pre-Sun). Astronomers are fairly confident that the nebular cloud formed a disk because similar structures have been detected around other stars.

During the collapse, gravitational energy was converted to thermal energy (heat), causing the temperature of the inner portion of the nebula to dramatically rise. At such high temperatures, the dust grains broke up into molecules and energized atomic particles. However, at distances beyond the orbit of Mars, the temperatures probably remained quite low. At -200℃, the tiny particles in the outer portion of the nebula were likely covered with a thick layer of ices made of frozen water, carbon dioxide, ammonia, and methane. Some of this material still resides in the outermost reaches of the solar system in a region called the Oort cloud.

The formation of the Sun marked the end of the period of contraction and thus the end of gravitational heating. Temperatures in the region where the inner planets now reside began to decline. The decrease in temperature caused those substances with high melting points to condense into tiny particles that began to coalesce (join together). Such materials as iron and nickel and the elements of which the rock-forming minerals are composed—silicon, calcium, sodium, and so forth—formed metallic and rocky clumps that orbited the Sun. Repeated collisions caused these masses to coalesce into larger asteroid-size bodies, called protoplanets, which in a few tens of millions of years accumulated into the four inner planets we call Mercury, Venus, Earth, and Mars. Not all of these clumps of matter were incorporated into the protoplanets. Rocky and metallic pieces that still remain in orbit are called meteoroids.

As more and more material was swept up by the inner planets, the high-velocity impact of nebular debris caused the temperatures of these bodies to rise. Because of their relatively high temperatures and weak gravitational fields, the inner planets were unable to accumulate much of the lighter components of the nebular cloud. The lightest of these, hydrogen and helium, were eventually whisked from the inner solar system by the solar winds.

At the same time that the inner planets were forming, the larger, outer planets (Jupiter, Saturn, Uranus, and Neptune), along with their extensive satellite systems, were also developing. Because of low temperatures far from the Sun, the material from which these planets formed contained a high percentage of ices—water, carbon dioxide, ammonia, and methane—as well as rocky and metallic debris. The accumulation of ices partly accounts for the large sizes and low densities of the outer planets. The two most massive planets, Jupiter and Saturn, had surface gravities sufficient to attract and hold large quantities of even the lightest elements—hydrogen and helium.

太阳系的有序性使得大多数天文学家得出这样一个结论:即行星基本上是在同一时间形成的,并且形成行星原始(原始)物质与太阳形成的原始物质相同。这种材料形成了大量的尘埃和气体,称为星云。星云假说认为太阳系中的所有星系都由巨大的星云组成,而星云中大部分是氢和氦,还有一小部分已知存在的所有其他的重元素。这种灰尘和气体云层中的重物质主要由硅,铝,铁和钙等元素构成,这些元素是现在常见的岩石材料。氧气,碳和氮等其他一些熟悉的元素也很普遍。 大约五十亿年前,一些外部影响,如来自破坏性爆炸(超新星)所带来的冲击波可能引发了巨大的气体云和重元素的微小颗粒的瓦解,由于颗粒之间的重力相互作用,导致云开始慢慢收缩。由于漩涡星云在慢慢地收缩,它旋转的速度越来越快,这与滑冰者在滑冰时将手臂拉向身体的原理相同。最终,重力的向内拉力与由星云旋转运动引起的外向拉力相平衡。此时,曾经巨大的云朵已经呈现出一个平坦的圆盘形状,其中心处存有大量的物质,称为原太阳(前太阳)。天文学家非常确定星云已形成了一个圆盘,这是因为他们已在其他恒星周围检测到类似的结构。 在瓦解过程中,引力能量转化为热能(热量),导致星云内部温度急剧上升。在如此高的温度下,尘埃颗粒分解成分子,并激活原子颗粒。然而,在火星轨道以外的地方,温度可能仍然非常低。在零下200℃时,星云外部的微小颗粒很可能会覆盖上一层由冷冻水,二氧化碳,氨和甲烷构成的冰层。某些材料仍然存在于太阳系最外层的一个称为奥尔特云的地区。 太阳的形成标志着收缩期的结束,因此也结束了引力加热。内行星所在地区的温度开始下降。温度下降导致高熔点物质凝结成小颗粒,开始聚合(连接在一起)。诸如铁和镍之类的材料以及成岩矿物所组成的元素 - 硅,钙,钠等- 形成了围绕太阳轨道周围的金属和岩石团块。这些团块的多次碰撞使这些群体聚合成了众多小行星大小的天体,称为原行星,几千万年后,沉积到了我们称之为水星,金星,地球和火星的四大内行星中。并非所有这些团块都被纳入原行星中。仍然留在轨道上的岩石和金属物质被称为流星体。 随着内行星扫荡了越来越多的物质,星云碎片的高速撞击使得这些天体的温度升高。由于天体的温度相对较高和引力场相对较弱,因而内行星无法积聚宇宙云中大部分的轻质组分。其中最轻的成分是氢气和氦气,最终,太阳风将这两种成分从太阳系内部中吹走。 在内行星形成的时候,更大的外行星(木星,土星,天王星和海王星)以及它们广阔的卫星系统也处于发展中。由于距离太阳远,温度低,这些行星中形成的物质含有大量的冰 - 水,二氧化碳,氨和甲烷 - 以及岩石和金属碎片。冰块的堆积在一定程度上解释了外部行星的大尺寸和低密度。两颗最大的行星,木星和土星,其表面重力足以吸引和保存大量甚至最轻的元素 - 氢和氦。

题目
1 2 3 4 5 6 7 8 9 10 11 12 13 14
6.According to paragraph 2, why do astronomers believe that the nebular cloud formed a disk around the protosun?
  • A.They can still see some debris from the disk.
  • B.They have observed that disks have formed around other stars.
  • C.They know that any rotating cloud of gas tends to contract into a disk shape.
  • D.They have conducted experiments with gravity that have confirmed their belief.
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    最新提问
    • wx_6697
      觉得B C 意思一样,不知道选哪个
    • wx_5576
      这道题C为什么对,E为什么不对?
    • wx_5576
      B为什么不能选啊?
    • wx_6697
      TPO30 passage 2 Q5我选的 D,不明白为啥不对?
    • wx_6697
      鑫哥,TPO6passage3Q5 答案是给错了吗?好多人都选A
    • wx_6697
      这题也很容易选错选成了D
    • wx_6697
      这道题A为什么错了
    • 芊儿
      为什么这道题不选c??a中的variety不是应该对应文中的differentiating 吗??求解!
    • wx_1000
      这道题不选E是因为太细节了吗
    • 王金阁
      这个题为什么不选C啊。。。
    • 芊儿
      这道题的D选项不是和文中的better able to reproduce in open settings相对应么??
    • 风荨火
      有大佬解释一下这个为啥选D嘛?
    • 以沫
      请问这个D 在哪里提现?为什么D错?
    • 芊儿
      第六题 的C选择为什么不对,感觉A是明显驳斥啊...
    • wx_6697
      鑫哥,这道题D是从哪里看出来的
    • wx_6697
      这题选的A,根据是Joly’s calculations clearly supported those geologists who insisted on an age for Earth far in excess of a few million years.想问鑫哥为啥不选A
    • wx_6697
      这题我选的是C依据是into a new habitat outside of its natural range, it may adapt to the new environment and leave its enemies behind.C为啥错了呢?鑫哥
    • wx_8861
      F选项的weather-related destruction在哪里体现了呢?原文最后一段的开头Among the costs里的costs是不是打错了?应该是coast?
    • wx_6697
      求问这道题B为啥不选,原文依据:viable seeds of pioneer species can be found in large numbers on some forest floors.
    • 与托福的斗争史
      与托福的斗争史 去解答 去解答
      这题为什么选C?
    • 小雨淅沥哗啦的下
      小雨淅沥哗啦的下 去解答 去解答
      B哪里错了
    • 小雨淅沥哗啦的下
      小雨淅沥哗啦的下 去解答 去解答
      B为啥不对
    • 李浩然
      B选项错误,是因为残缺么?
    • wx_100
      请问在做题的时候如何排除c呢。看了答案,感觉是该选a的,但是当时做题脑子一热,就特别钟爱c,也没看其他选项。。求敲醒。。
    • wx xxxxx
      请问鑫哥,这段开头有写As one pesticide replaces another为什么不是对应a new pesticide is developed?
    • wx_7695
      鑫哥,从哪里看出来这个masks 不是use呀,原文说了wear呀
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      @鑫哥,这题the damage will continue 不应该对应前面的 the target species evolves resistance to it,然后As one pesticide replaces another,不应该是结束了time cycle 吗
    • wx_2065
      鑫哥,想知道E错在哪里?
    • wx_7695
      鑫哥,B选项 cannot extended to earlier geological periods. 原文说的意思是后来的进化无法估计吧
    • wx_2163
      B为什么不选
    • wx_7780
      鑫哥,这个哪里看不use了。BD是修饰错,C是无中生有,怎么能直接选出A?
    • 100
      看到第一句话,以为是中心句就选了A... 为什么不能选A呢
    • 100
      为什么选b?
    • gu33
      请问下 这里选D的原因是 因为 evolutionary approach 对应着 原文的 Rates of evolution 嘛? 这里我选了C。。不是很懂 插入句和 D的关系 求解答
    • 我是啦啦啦
      我是啦啦啦 去解答 去解答
      这个题A哪里错了?是因为主语不对吗?这个C比A多一步推理啊
    • haiyuqiao
      鑫哥,D选项里的19世纪出现了很多假设,原文中并没有提到啊
    • wx_7060
      为什么选a 呢。我觉得a是细节。F哪错了?
    • wx_1105
      我想问一下,这道题为什么不能选A呢?
    • wx_8122
      D为什么不选
    • wx_1655
      f选项哪里说了
    • chaulaw
      鑫哥,原文是below经济损害水平,D是一触发经济损害就用,这也对吗?
    • chaulaw
      interclan婚姻是对的吗?不是只在自己的family结婚扩大家族吗?
    • wx_6697
      鑫哥,这道题答案是不是错了,好多人选D 我也选的D求解答
    • wx_6697
      这道题应该是一道易错题,每个选项的都有,然而我选的A错了,求解
    • wx_6697
      鑫哥,这题的C是怎么得到的?B也没有找到啊?难道不是应该选B
    • wx_6697
      鑫哥,还有这个,好多人选A答案是不是错了
    • wx_6697
      求问D是从哪里得出来的,我选的B呀哎呀
    • wx_4185
      it is difficult to say how far they were intended to be portraits rather than generalized images 这句话怎么理解呢
    • 此楠楠
      请问下这个插入题怎么选的呢?
    • 此楠楠
      求鑫哥讲解下A选项。。。 Even though in error, Joly’s calculations clearly supported those geologists who insisted on an age for Earth far in excess of a few million years.