Young-earth "proof" #11: Since the earth's magnetic field is decaying at an exponential rate, its strength would have been unrealistically high 25,000 years ago. Thus, Earth is less than 25,000 years old.
11. Dr. Hovind is almost certainly talking about Barnes's magnetic field argument (1973) or some echo of it. Henry Morris, himself, once praised it as one of the best arguments for a young earth.
In 1971 Barnes took about 25 measurements of the earth's magnetic field strength (originally assembled by Keith McDonald and Robert Gunst (1967)) and fitted them to an exponential decay curve. He drew upon Sir Horace Lamb's 1883 paper as theoretical justification for this. Following the curve backwards in time, Barnes showed that 20,000 years ago the earth's magnetic field would have been impossibly high. Thus, he concluded that the earth is much younger than 20,000 years.
There are several fatal errors in Thomas G. Barnes's work:
1. Barnes employs an obsolete model of the earth's interior. Today, no one doing serious work on the earth's magnetic field envisions its source as a free electrical current in a spherical conductor (the earth's core) undergoing simple decay. Elsasser's dynamo theory is the only theory today which has survived.
According to Barnes, "In 1883 Sir Horace Lamb proved theoretically that the earth's magnetic field could be due to an original event (creation) from which it has been decaying ever since" [1973, p.viii]. This is not a correct description of Lamb's 1883 paper, which dealt only with electric currents and did not mention geomagnetism at all...
Lamb's ideas on electric currents had simply been pressed into service to support Barnes's obsolete ideas about the origin of the earth's magnetic field.
In trying to discredit Elsasser's theory, Barnes quoted Cowling's theorem.
He cites Cowling's 1934 theorem that shows "that it is not possible for fluid motions to generate a magnetic field with axial symmetry (such as the dipole field of the earth)" (Barnes 1973, pp. 4445). However, recent work shows that Cowling's theorem does not forbid a model with axially symmetric fluid motions generating a field with lower symmetry (Jacobs 1975, pp. 12831), and, indeed, the earth's field does not have a pure dipole character, a fact that Barnes conveniently ignores.
The dynamo theory has gained nearuniversal acceptance because it is the only proposed mechanism that can explain all the observed features of the Earth's magnetic field. In contrast, Barnes' hypothesis of a freely decaying field cannot explain the existence, configuration, movement, or changes in the nondipole field, the fluctuations in the dipole moment, the reversals in field polarity, or the documentation in the geologic record of the continued existence of the field for more than three billion years.
Point 1, all by itself, is fatal to Barnes's basic idea since it removes any serious reason for believing that the earth's magnetic field has been continuously decaying.
2. In using McDonald and Gunst's data, Barnes selects only the "dipole component" of the total magnetic field for analysis (Brush, 1983, p.73). The dipole field is not an accurate measurement of the overall strength of the earth's magnetic field. The dipole field can decay even as the overall strength of the magnetic field remains the same!
...McDonald and Gunst state explicitly that "the magnetic dipole field is being driven destructively to smaller values by fluid motions which transform its magnetic energy into that of the near neighboring modes rather than expend it more directly as Joule heat" (1968, p.2057). In other words, the energy is being transferred from the dipole field to the quadrupole field and to higher moments rather than being dissipated as heat. This implies that the value of the dipole field could not have been much greater in the past, since it is limited by the total magnetic energy, which does not change very rapidly.
Thus, we are not dealing with a simple decay. Energy is being shifted to other modes rather than being totally lost to the magnetic field. Might not a reverse shift in energy increase the dipole field at times?
There is some reason to believe that the dipole field reached a maximum around 1800 and that it was smaller in 1600 than in 1800 (Yukutake 1971, p.23). Other recent work also suggests that the dipole field has fluctuated on a fairly short time scale (Braginsky 1970; papers by J. C. Cain and others in Fisher et al. 1975).
It seems that the dipole field has gone uphill at times!
Studies of the magnetic field as recorded in dated rocks and pottery have shown that the dipole moment actually fluctuates over periods of a few thousand years and that decreases in field intensity are eventually followed by increases. For example, the archaeomagnetic data show that the dipole field was about 20% weaker than the present field 6,500 years ago and about 45% stronger than the present field about 3000 years ago (McElhinny and Senanayake, 1982).
Quite clearly, the dipole field has increased at times!
Point 2, by itself, is fatal to Barnes's idea in that Barnes was not actually plotting a decline in total field strength. Evidence shows that the dipole field has increased in strength at times.
3. Based on his preconceptions of the earth's magnetic field, Barnes fits an exponential decay curve to the data. Barnes is doing some circular reasoning here. The use of an exponential decay curve is tantamount to assuming that the earth is young; one must show that the decay curve arises from the data not assume it! Otherwise, one is guilty of assuming that which must be proven, of arguing in circles.
If you actually plot the data, as Brush has done (1983, p.74), it becomes quite clear that the data does not justify an exponential decay curve. To be sure, the data doesn't actually rule out an exponential decay curve, but that's not particularly helpful since the data can be made to fit any number of radically different equations. We could fit it to some kind of sine function if we wanted to. For example: f(x) = A sin(Bx + C) would also fit the data for suitable values of A, B, and C. A scientific handling of the data requires that we don't play guessing games. We must use the simplest curve (usually favored by nature) that the data justifies. In this case, the data fits a linear curve (straight line) just as well. Thus, Barnes should have used a straight line. Even then, a careful scientist would not extrapolate very far beyond the limits of the data unless there was good justification for it.
Do the data actually fit this exponential formula? Barnes gives no evidence that they do; in fact, he does not even bother to present a plot showing the experimental points in relation to his theoretical curve. When one does construct such a plot (fig. 1) it becomes immediately obvious that the fit is not very good and that a straight line ... is equally good, considering the scatter of the observational points. Indeed, that is what McDonald and Gunst themselves stated: "Since the time of Gauss's measurements the earth's dipole moment has decreased, sensibly linearly, at approximately the rate of 5 percent per hundred years" (quoted by Barnes 1973, p.34).
Thus, instead of limiting the earth to less than 20,000 years of age, a more objective use of the data, a linear extrapolation, leads to 100 million years. However, both conclusions involve errors of procedure since there are no justifiable grounds for extending the curve great distances beyond the actual data. That amounts to pure speculation, which proves nothing.
Point 3, alone, deprives Barnes's idea of any force, turning it into wild speculation.
4. Barnes simply ignores the fact that the earth's magnetic polarity has reversed itself on numerous occasions. That fact, alone, is absolutely fatal to every fibre of Barnes's argument.
The theoretical basis for magnetic field reversals is Elsasser's dynamo theory, which is based on fluid motions in the earth's core (Elsasser 1946-1947; see Jacobs 1975, chap. 4, or Stacey 1977, chaps. 5 and 6). The dynamo theory assumes an energy source to keep the fluid moving; it is not yet established what the main source of energy is, but there are various possibilities such as radioactive heating, growth of the inner core, differential rotation of the core and mantle, etc. In any case, nothing justifies Barnes's assumption that there is no energy source.
Barnes, like most creationists, is not above quoting obsolete sources. In a 1981 paper he made extensive use of a 1962 book by A. Jacobs which cited difficulties with the magnetic reversal hypothesis (Brush, 1983, p.76). Funny, that Barnes should quote a 1962 source. It was in the mid1960s when the great discoveries started rolling which forever made magnetic reversals a fact of life! Odd, don't you think, that Barnes missed all those more recent sources? I guess they were not particularly "helpful."
In the same section of the later edition of this book, Jacobs states that "the evidence seems compelling" that such reversals have occurred (1975, p. 140). Barnes, however, omits the date of publication of the text he quotes from and completely ignores the fact that Jacobs changed his position in the 1975 edition. In fact, the principal creationist "expert" on geomagnetism writes as if the "revolution in the earth sciences" of the last two decades had never happened; he quotes A. A. [Meyerhoff] and Howard Meyerhoff, two diehard opponents of plate tectonics, as if their "refutations" actually had been successful.
Actually, considering that Barnes rejected modern relativity theory, quantum mechanics, and just about anything this side of nineteenthcentury physics, it's not too surprising that he also rejected the revolution in geology. Barnes was born at the wrong time; I do believe he would have been happier in the nineteenth century.
Two years later, despite criticism from Brush, we find that Barnes is still ignoring the fact that Jacobs had changed his views. If someone concluded that Barnes was less than honest, could you blame that person?
In the January 1982 issue of Journal of Geological Education, Stephen Brush cites, as well as criticizing Barnes' "theory", that Jacobs accepted reversals once the evidence was overwhelming. However, in his book Origin And Destiny Of The earth's Magnetic Field , Barnes (1983b) rejects Brush's criticisms citing again Jacobs' 1963 objections, but omits the date and ignores the 1975 revision! In fact, in 1984, Jacobs wrote a book entitled Reversals of the Earth's Magnetic Field.
Point 4, just by itself, is absolutely fatal to Barnes's idea in that it destroys the theoretical foundation for believing that the earth's magnetic field is continually decaying. In supporting the dynamo theory it also destroys any justification to read into the data a continual decline in field strength.
We can safely relegate Barnes's magnetic field argument to the junk heap of crackpot ideas. Barnes' work lacks the scientific integrity, competence, and judgment one expects from a scientific work.
Last updated: Thursday, 10-Mar-2011 15:57:29 CST
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