Sunday, March 22, 2009

The Delk Print, again

A page on the subject at www.paleo.cc. Comments include:

The last photo in the set posted by David Lines set shows the Delk slab in relation to several cross sectional scans http://linesden.com/cem/delk/delk_ct_scan_long.pdf (lines, 2008). Although the scan images are rather small in relation to the slab image, making it difficult to confirm certain details, the following observations seem possible. First, the most distinct bands of light color seem to occur most of the rock edges, including areas of its surface, sides, and bottom, even where no depression occurs. This seems to strongly imply that light areas do not necessarily indicate compression or greater density. Indeed, some scans seem to not only lack light bands, but actually show darker regions immediately under the dino print and "big toe" depressions, whereas one would expect light bands if pressure from they were made by foot or digit pressing in sediment. Furthermore, one can see from "Slice 139," which cuts through the middle of the "big toe" depression, that this feature is incredibly deep compared to the other toe marks. The track advocates would have to explain how the big toe could impress that far, and yet leave relatively shallow toe prints on a much higher plane (besides being situated at an odd angle and much farther from the rest of the print than in a normal print).

What seems to have been missing in the CT procedures are proper controls, including comparable scans of known real prints, and known carved prints in similar limestone (including ones with applications of acid and other substances), to better understand the scan results. One important question is what degree and depth density changes are normal or expected in real fossil prints? Another is, were the CT scans calibrate to properly detect them? Medical scans are calibrated for tissue and bone--which are much less dense than rocks. Were they recalibrated in this case? On what standard or basis? What CT numbers correspond to what densities levels and levels of brightness on the scan. There appear to be many important details missing from the reports and videos of the print supporters.

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