听写材料28.月亮的起源

正确原文：

Theorigin of earth’s moon, the largest moon in the solar system, is stillsomething of a mystery. There are some theories about its origin, however. Now,keep in mind that a theory of the moon’s origin has to be consistent with twoimportant facts. The first fact is that the earth contains a lot of iron. Mostof it has an iron core. But the moon contains practically no iron. The secondfact is that, other than the difference in iron content, the moon and earth arecomposed of essentially the same minerals, a similarity not shared with anyother planet or moon in our solar system. One of the earliest theories of themoon’s origin, I call it the Capture Theory, proposes that the moon was somehowcaptured by earth’s gravitational force. This theory is improbable, however, becauseit assumes that the moon and earth formed in different parts of the solarsystem. If this were true, you would expect the moon’s composition to be muchdifferent from earth’s composition, just as all the other planets in the solarsystem are so different from earth. A second theory of the moon’s origin ismore promising. It is sometimes referred to as the Mars Theory, because accordingto this theory, when earth was still molten, it was struck by a planet aboutthe size of Mars. The impact caused the cores of the two planets to melt togetherand chunks of earth’s crust to be thrown out into space. These chunks cametogether to form the moon. Now remember, earth’s crust is low in iron becausethe iron is in earth’s core, but high in various other minerals. This thenaccounts for why there is little iron but lots of other minerals on the moon.

生词摘录：

1.    origin: n. 起源，开端

2.    solar system: 太阳系

3.    iron: n. 铁

4.    iron core: 铁心，铁核

5.    mineral: n. 矿物质

6.    Capture Theory: 捕获说

7.    gravitational force: 重力，地心引力

8.    composition:n. 组成，成分

9.    Mars Theory: 火星理论，火星说

10.  molten:adj. 熔化的，炽热的

11.  chunk:n. 大块碎片

12. earth’s crust: 地壳