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月球理论 【背景知识】
V1：
月球理论
第一段：1960阿波罗登月前有3个理论叫，condensation，fossal?,capture...然后说了各自的特点。
第二段：登月后发现这3理论都有缺陷
第三段：后来提出了新的理论叫collision，很好了说明了月球的起源。。
第1题：文章的结构是哪个？这个很简单，所以一定是低分库的题，哎。
【背景知识】
Question:
Where did the Moon come from?
Answer:
Any theory which explains the existence of the Moon must naturally explain the following facts:
The Moon's low density (3.3 g/cc) shows that it does not have a substantial iron core like the Earth does.
Moon rocks contain few volatile substances (e.g. water), which implies extra baking of the lunar surface relative to that of Earth.
The relative abundance of oxygen isotopes on Earth and on the Moon are identical, which suggests that the Earth and Moon formed at the same distance from the Sun.
Various theories had been proposed for the formation of the Moon. Below these theories are listed along with the reasons they have since been discounted.
The Fission Theory:月球是从地球喷出去的 从大西洋那块 因为月球组成很像地球的地函而且经由旋转而喷出也是有可能的 但是却有疑点 一点是有关两者化石的差异 一点是有关一些BAKING 的物质 This theory proposes that the Moon was once part of the Earth and somehow separated from the Earth early in the history of the solar system. The present Pacific Ocean basin is the most popular site for the part of the Earth from which the Moon came. This theory was thought possible since the Moon's composition resembles that of the Earth's mantle and a rapidly spinning Earth could have cast off the Moon from its outer layers. However, the present-day Earth-Moon system should contain "fossil evidence" of this rapid spin and it does not. Also, this hypothesis does not have a natural explanation for the extra baking the lunar material has received.
The Capture Theory:月亮是在太阳系的其他地方生成的 但是却被地球的磁场给拉过来 这个就可以解释化学成分不同 但是要把月球吸过来是不容易的 This theory proposes that the Moon was formed somewhere else in the solar system, and was later captured by the gravitational field of the Earth. The Moon's different chemical composition could be explained if it formed elsewhere in the solar system, however, capture into the Moon's present orbit is very improbable. Something would have to slow it down by just the right amount at just the right time, and scientists are reluctant to believe in such "fine tuning". Also, this hypothesis does not have a natural explanation for the extra baking the lunar material has received.
The Condensation Theory:在同一个地方形成的 但是疑点是其实形成的很不同 This theory proposes that the Moon and the Earth condensed individually from the nebula that formed the solar system, with the Moon formed in orbit around the Earth. However, if the Moon formed in the vicinity of the Earth it should have nearly the same composition. Specifically, it should possess a significant iron core, and it does not. Also, this hypothesis does not have a natural explanation for the extra baking the lunar material has received.
There is one theory which remains to be discussed, and it is widely accepted today.
The Giant Impactor Theory火星撞到地球 然后喷出一些东西 这些东西接着形成了月球 (sometimes called The Ejected Ring Theory): This theory proposes that a planetesimal (or small planet) the size of Mars struck the Earth just after the formation of the solar system, ejecting large volumes of heated material from the outer layers of both objects. A disk of orbiting material was formed, and this matter eventually stuck together to form the Moon in orbit around the Earth. This theory can explain why the Moon is made mostly of rock and how the rock was excessively heated. Furthermore, we see evidence in many places in the solar system that such collisions were common late in the formative stages of the solar system. This theory is discussed further below.
More About The Giant Impactor Theory
In the mid-1970s, scientists proposed the giant impact scenario for the formation of the Moon. The idea was that an off-center impact of a roughly Mars-sized body with a young Earth could provide Earth with its fast initial spin, and eject enough debris into orbit to form the Moon. If the ejected material came primarily from the mantles of the Earth and the impactor, the lack of a sizeable lunar core was easily understood, and the energy of the impact could account for the extra heating of lunar material required by analysis of lunar rock samples obtained by the Apollo astronauts.
For nearly a decade, the giant impact theory was not believed by most scientists. However, in 1984, a conference devoted to lunar origin prompted a critical comparison of the existing theories. The giant impact theory emerged from this conference with nearly consensus support by scientists, enhanced by new models of planet formation that suggested large impacts were actually quite common events in the late stages of terrestrial planet formation.
麻烦版主看看这是不是月球形成那篇 我从2010年的二月狗狗挖到的~~ |
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发表于 2010-4-9 00:26:37
