From: bivalve (firstname.lastname@example.org)
Date: Tue Mar 25 2003 - 14:43:58 EST
>Are you saying 1) the rapid changes in magnetic polarity are reasonable, or 2) the radiometric dates for the rocks are way off or way uncertain? <
I think that rapid changes in magnetic polarity are implausible and that radiometric dating, when used properly, is very reliable. (Using 14C dating on late Paleozoic wood in an effort to slander radiometric dating is not using radiometric dating properly.) I do think that a young earth advocate could take various internally consistent positions, not that I find them plausible. These include:
The magnetic patterns and the geologic column were largely created as is. Only the very surficial deposits actually reflect past events. This raises questions of why, deceptive appearance, etc. but is irrefutable.
Magnetic reversals and everything else in the geologic record occurred extremely rapidly either through totally unknown physical processes that allow apparent violation of fundamental laws of physics or through miracles. The hope for someday finding a young-earth explanation seems highly optimistic in light of the consistent results of the past quarter millennium or so of scientific study, but it is true that we do not know what will be discovered tomorrow.
Geologic evidence for magnetic reversals, etc. is an unexplained mystery. Simply admitting that you have no explanation is an honest answer. The difference between this and the previous is not large; perhaps "I have no idea" versus "I do not know, but I intend to find out".
Any of these approaches can reconcile a young-earth position with any particular piece of evidence. All of these involve admitting that the physical evidence actually does not favor a young-earth interpretation to the best of our knowledge, though possibly holding out optimism for future discoveries.
I do consider the magnetic reversal pattern to be a good argument for an old earth. However, I do not think that one has to accept an old earth to admit that the magnetic reversal pattern exists. My intended point was to question the accusation (which was not made here) that anyone who doubts the accuracy of any YEC science claim is doing so solely because he has sold out to evolution.
>My understanding is that there are by now lots of core samples from deep sea drilling that have been radiometrically dated. These cores very likely have been tied to the paleomagnetic striations of the ocean floor. (I have to waffle because I'm not intimately familiar with the results of these studies; but I'd be very surprised if such studies hadn't been done.)<
Direct radiometric dating of seafloor basalts can be difficult, if you succeed in getting a core down to basement. However, the overlying sediment provides abundant evidence of the age, so the dates are very well constrained. Terrestrial lava flows are very good for both magnetic and radiometric dating, though they lack the continuous magnetic record of the seafloor. Sedimentary deposits can often be dated magnetically and may have material suitable for radiometric dating (volcanic ash, glauconite, 14C or U-Th depending on the age, etc.) in addition to fossils, geochemical events, etc. that can be used to correlate to known radiometric dates. Dates of major magnetic reversals from the mid-Mesozoic to the Recent are thus fairly certain. Very brief reversals may not be well-documented, and the seafloor spreading evidence gives a continuous record back only to the mid-Mesozoic. Earlier magnetic reversals are thus more difficult to correlate, though concatenation of data f!
rom major outcrops (or core sections) can give good ideas for at least certain intervals. To put it more briefly: the dates of the magnetic reversals observed in the seafloor record are very well constrained by radiometric dating, but not necessarily by radiometric dating of seafloor rocks.
Dr. David Campbell
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Tuscaloosa, AL 35487-0345 USA
That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa
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