Young-earth "proof" #5: The Moon is receding a few inches each year. Less than a million years ago the Moon would have been so close that the tides would have drowned everyone twice a day. Less than 2 or 3 million years ago the Moon would have been inside the Roche limit* and, thus, destroyed.(Dr. Hilpman vs. Dr. Hovind, June 15, 1992; the Royal Hall of the University of Missouri)
Once again, Dr. Hovind's figures just boggle the mind! Let us assume, for the sake of argument, that the Moon is receding at 6 inches per year. If we go back a million years, then the Moon was 6 million inches closer to the earth. That comes to about 95 miles! Since the Moon is about 240,000 miles away, that doesn't amount to diddlysquat! Indeed, the Moon has a slightly elliptical orbit that varies more than 95 miles all by itself.
A more accurate estimate, based on the present rate of lunar recession, puts the Moon within the Roche limit around 1 or 2 billion years ago. That is the argument most creationists use. (Since Dr. Hovind's notes match the figures he quoted in his debate with Dr. Hilpman, they are fair game and not a simple slip of the pen.)
The tides, chiefly caused by the Moon's gravitational attraction and the orbiting of Earth and Moon about a common point, act as a brake to slow down the earth's rotation. The nearer tidal bulge, which carries the greater effect, runs slightly out of alignment of the Moon overhead; the gravitational interaction between it and the Moon serves to speed up the Moon in its orbit even as it slows down the earth's rotation. As it speeds up, the Moon moves to a higher orbit.
The effectiveness of this tidal brake on the earth's rotation strongly depends on the configuration of the oceans. Thus, we should inquire as to whether the current arrangement is an average value or not.
The present rate of tidal dissipation is anomalously high because the tidal force is close to a resonance in the response function of the oceans; a more realistic calculation shows that dissipation must have been much smaller in the past and that 4.5 billion years ago the moon was well outside the Roche limit, at a distance of at least thirtyeight earth radii (Hansen 1982; see also Finch 1982).
Thus, our moon was probably never closer than 151,000 miles. A modern astronomy text (Chaisson and McMillan, 1993, p.173) gives an estimate of 250,000 kilometers (155,000 miles), which agrees very closely with Brush's figure. Thus, the "problem" disappears!
It may surprise you to learn that Charles Darwin's second son, George Darwin, regarded by many as the father of geophysics, studied the Moon's tidal effects in great detail. He came up with the idea that the Moon broke away from the earth due to rapid rotation (the fission theory), and estimated that at least 56 million years would be required for the Moon to have reached its present distance. George Darwin regarded his view of the Moon's origin as nothing more than a good guess, and he considered his time estimate to be nothing more than a lower limit. In the nineteenth century such a calculation of the earth's age was a reasonable scientific exercise. Today, in the light of what we now know, it's an exercise in futility. Too bad "scientific" creationists don't keep up with these little details. For more insight into the problem, see Dalrymple (1991, pp. 48-52).
* The Roche limit is a distance of 2.44 times a planet's radius, as measured from the center of the planet. Within that distance an orbiting body, if chiefly held together by gravity, will be pulled apart.
Last updated: Thursday, 10-Mar-2011 15:57:25 CST
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