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希望对大家理解有帮助些...
三种理论都说了.且一一反驳.和jj反驳可以对上号.
暂时没找到如何两两反驳.
* The fission theory. First proposed in 1880 by Charles Darwin's grandson George, this theory holds that the original molten earth was spinning so fast that a chunk of it bulged outward and was flung skyward. Some offered the fission idea as a way of accounting for the vast hollow of the Pacific Ocean, until that was explained more neatly by continental drift. The biggest problem with the fission theory was that it required a much bigger angular momentum, or total rotation energy, than is seen now in the earth-moon system, and physicists know that angular momentum in a closed system cannot be gained or lost.
* The double planet theory. The moon formed independently in earth orbit as the primordial cloud gathered. The problem was that two bodies formed at the same place and time should be made of the same stuff. Astronomers already knew the earth and moon to have disturbingly different compositions. The earth has a dense iron core with 30 percent of its total mass, while the moon's iron core, if it exists, is much smaller.
* The capture theory. A body from elsewhere in the solar system came winging by and the earth's gravity captured it into orbit. The problem here was dynamical: as objects fly around the solar system, it is easy to get collisions and near collisions, but extremely difficult to get a capture.
貌似另外个版本更好 更jj上的首字母提取沾边些
For a long time, these three models had been accepted as possible lunar origins. However, later research gave a number of points that spoke against them.After the Apollo program, rock samples taken from the Moon revealed two important things:
- The Moon lacks iron. This is important to note because the Earth, in comparison, has a lot of it (in the core).
- The Moon and the Earth have exactly the same oxygen isotope composition.
Along with calculations in the field of energy and angular momentum, these two points spoke against the "Big Three" hypotheses as follows
Consequences for the Fission Hypothesis
Since the material that spun off the Earth would have come from the mantle, the lack of iron would not have been a problem (Earth's iron drained towards the core early on, leaving a depleted mantle).[2] This would also explain why the Moon has such a small core.[1] For obvious reasons, the theory also covers the issue of the oxygen isotope composition.
However, the total angular momentum today is too small to back this hypothesis.[3]
Consequences for the Capture HypothesisEven ignoring the very small chance of a planet easing into an Earth orbit like our Moon did, this hypothesis fails to explain the oxygen isotope similarity and also leaves open the issue of the Moon's small core.[1]
Consequences for the Coaccretion HypothesisThis model does not require extreme chances like the Capture theory and explains nicely why Earth and Moon share their oxygen isotope composition. However, there are open questions regarding the angular momentum, and the lack of iron spoke against it, too (It should be mentioned that this issue had been addressed recently, see Current Status.).[1] |
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发表于 2012-4-11 05:48:16
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