Date: 05 Apr 94 04:10:13 To: All Subject: Review: Origins 20(1) Origins 20(1) Winter 1993

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Date: 05 Apr 94 04:10:13 From: Donald Lindsay To: All Subject: Review: Origins 20(1) From: (Donald Lindsay) Organization: School of Computer Science, Carnegie Mellon Origins 20(1) Winter 1993 pp. 6-21 "An Alternative Explanation of Oceanic Magnetic Anomaly Patterns" by Norm Smith and Jane Smith Review by Don Lindsay This article begins by explaining that there is a heck of a lot of evidence that the ocean floor is being slowly created at long volcanic fissures, such as the one down the Mid-Atlantic Ridge. They pass briefly over the fact that this also ties cleanly in to a lot of other evidence. They claim that there is a shortage of direct measurements: that is, magnetic measurements (or radioactive datings) of actual samples, or even in-situ magnetic measurements made up-close to the actual ocean floor. I'm not enough of a geologist to claim otherwise without searching the literature, but I certainly had the impression that we possess many direct measurements. I know we've dated samples. In any case, the article eventually gets to its actual suggestion, which is that a single linear magnetometer flight yields a graph that looks a lot like band-limited noise. [These are signal artifacts from trying to measure a too-high-frequency signal.] This idea is defended by pointing out that an airborne magnetometer is kilometers above the bedrock, and is hence measuring an average taken across a large area. At this point, I should explain my qualifications. I did some of the digital filtering for the 1969 Canadian magnetometer flights across the Atlantic. I have since had professional involvement in areas that are mathematically related, such as acoustic signal processing. The article is correct in saying that such noise can occur. In fact, we used a digital band filter: this to eliminate noise sources such as the ocean waves beneath the aircraft. (We could equally have eliminated everything but the waves, and produced a graph of wave height along our flight path.) There are indeed conceivable geologic circumstances which would have introduced noise into our filtered results. I will return to this point. The conventional explanation is that the sea floor is being produced along such ridges, and is pushed away from the ridge as more rock arrives. As molten rock cools to below its Curie point, it acquires a magnetic direction, under the influence of the earth's magnetic field. [This has been directly observed on land.] The banding of the graphs is interpreted as evidence that the earth's magnetic field has reversed direction at intervals, thus causing parallel bands on the sea floor. The article then suggests that a ridge might have produced physical features which parallel the ridge, but by means other than sea floor spreading. They admit that the features may be "tens or even hundreds of kilometers long parallel to a ridge yet separated by only a few kilometers perpendicular to a ridge". Assuming that these features exist, the authors go on to do a computer simulation. They assume that the rock has magnetic variations on a much finer grain than the averaging window, but that the each physical feature is distinct magnetically (by virtue of amplitude values). This simulation yields results that resemble the magnetic measurements in the literature. From this, they conclude that their simulated geology is as reasonable as the conventional one, and that the jury should remain out on the conventional explanation. From the signal-processing perspective, this is semi-reasonable. The existence of fine-grained variations seems to be no more of an assumption than any other. However, from the physical perspective, it replaces something which is known to occur on land, with an unknown mechanism. Possible, no doubt: but unknown. Furthermore, this unknown mechanism must operate reliably and uniformly, because if it sometimes does not, then this non-operation would show up in our measured data. If we assume that this mechanism does exist, what is in doubt? - Not sea floor spreading. The article suggests that stresses and strains near the ridge are their alternate explanation for the parallel features. This does not begin to explain why the features should retain symmetry about the Mid-Atlantic Ridge, a thousand kilometers from the Ridge. It also does not explain why the rock nearer the Ridge should be younger than the rock nearer the continents. - Not continental drift. That is proven conclusively, not by knowledge of its mechanism, but by the existence of matching geological formations on the now-separate continents. The fact that the continents are *now* in motion (at exactly the right speed) is clear evidence that some mechanism does exist. - Not magnetic reversals. Their existence is known from land data. In short, this article proposes an unknown mechanism, in place of a known one, and claims that field data does not yet preclude it. That seems to be true, but no reason is given why the unknown mechanism is to be preferred as an explanation. Furthermore, should field evidence prove this idea correct, nothing important will be different: North America will continue towards China: the sea floor will spread (what else, stretch?): and magnetic reversals will still have actually occurred. It would indeed be nice to get better field data, and I would not wish to discourage Creationists from assisting in the funding of oceanographic research. -- Don D.C.Lindsay Carnegie Mellon Computer Science


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