The Origin of the Moon

Three basic theories offer an explanation for the origin of the moon. Each theory is able to account for certain aspects of the present earth-moon system, but when extrapolations back into the past are made, each theory develops serious conflicts with physical laws; especially the “law” of gravitation.

The first theory maintains that the moon was once a planet, with an orbit around the sun similar to that of the earth. At some time in the not too distant past (less than two billion years ago), the moon came too close to the earth, and was “captured” by it. This theory, while perhaps possible, can be virtually ruled out by the law of probability. For such a capture to occur, the velocities, forces, and relative positioning of the earth, moon, and sun would have to have been so delicately balanced that such a coincidence would be nearly impossible. It is far too likely that the moon would have either collided with the earth, or passed very near it, and then continued on its way around the sun without forming an earth orbit. Even if hundreds of bodies the size of the earth and with similar orbits were circling the sun, the chances that one of these bodies would form an orbit around the earth would not appreciably increase. A collision, while highly improbable, would have been far more likely than a capture. Also, it seems virtually certain that an earth-moon collision occurring less than two billion years ago would have left ample evidence in the geologic record. Such a cataclysm would have left a worldwide layer of sedimentation and volcanic ash that would be clearly unmistakable.

The second theory maintains that the moon, once part of the earth, was formed by a fission of the earth, caused by centrifugal force. The major problem with this theory is that for the earth to develop enough centrifugal force to cause it to fission, it would have to have a period of rotation of about two hours. This means that, at the time of fission, which would have to be less than two billion years ago, the earth-moon system would have to have had an angular momentum over four times what it is at present. It is virtually impossible to conceive of a mechanism by which the system’s angular momentum could be so decreased in the intervening time period.

The third theory is, perhaps, the most appealing, since it is more in keeping with the concept of an evolutionary universe, in that it does not entail either extreme chance or cataclysmic events. This theory proposes that the earth and the moon were formed as a two planet system, each born as an individual body but associated in space with each other. They werebuilt up by an accretion of matter from the same primal solar cloud. However, two major objections to this theory arise out of the nature of the principle of gravitation.

Firstly, according to gravitational theories, the earth has a substantially greater density than the moon. But if they were formed out of the same cloud of matter, they would necessarily have similar densities, which they do not.

The second objection, which supplies the limiting factor of two billion years for the first two theories, concerns the effects of tidal friction. Studies that have been made of the ratios’ of uranium and lead isotopes in rocks taken from both the earth and the lunar surface indicate that both bodies have similar ages of about five billion years. However, another way that the age of the earth-moon system can be calculated is by the effects of tidal friction.

Tidal friction causes the moon to move farther and farther away from the earth as it picks up angular momentum from the earth’s rotation. In this process the earth’s rotation about its axis is slowed, and the angular momentum lost from the earth is gained by the moon’s orbital motion. If the effects of tidal friction are extrapolated back into the past, they place a maximum age on the system of 1.78 billion years. According to gravitational theories, 1.78 billion years ago the moon would be at the Roche’s limit, or 15,700 kilometers from the earth. At this distance, gravitational forces would tear the moon to pieces and it would become a ring around the earth similar to those of Saturn. The tidal friction created by gravitation would be inversely proportional to the cube of the distance between the earth and the moon. However, the tidal friction created by electrostatic repulsion would be inversely proportional to the square of the distance between the two bodies. When the effects of tidal friction produced by electrostatic repulsion are extrapolated back into the past they place a maximum age on the system at over six billion years.

Using Absolute Motion Theory, it is possible to conclude that the earth and the moon were formed as a two planet system, over the same period of time, by a gradual buildup of matter from the same basic cloud of solid particles. These particles gradually expanded into one another until the earth-moon system was formed.

The maximum age of the earth-moon system can be determined by extrapolating the effects of tidal friction into the past. The system can be no older than the time that it would take for the moon to reach its Roche limit. Gravitational theories, which show tidal friction to be inversely proportional to the cube of the distance between the bodies, place the maximum age at 1.78 billion years. Absolute Motion Theory, which shows tidal friction to be inversely proportional to the square of the distance, places the maximum age of the earth-moon system at about 6.5 billion years. This result is in keeping with radioactive isotope studies that show the earth and moon to be about 5 billion years old. According to the electrostatic theory of tidal forces, 5 billion years ago the moon and the earth would have been about 200,000 km apart.

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