Dating for the Birds

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Dating for the birds as fossil footprint re-dating reported in Nature vol 495, Brief Communication Arising, E1, 21 March 2013, and Nature vol. 501, p262, 12 September 2013. In 2002 a group of Argentinian geologists published a paper in Nature describing many hundreds of bird-like footprints in Santo Domingo Formation of northwest Argentina, which was dated by 40Ar/39Ar radioactive method, as Late Triassic, approximately, 212 million years old. This was 55 million years prior to what was believed to be the oldest bird fossil. At the time the researchers concluded “these bird-like foot prints can only be attributed to an unknown group of theropods showing some avian characters”. See our report “Footprints Precede Feet” here. (Theropods are dinosaurs.)

Further study of these footprints, published in 2009 by a team including the three original researchers, revealed the fossil footprints had all the features of tracks left by shore birds as they landed, walked, probed and took off on a muddy shore. The researchers concluded: “The recognition of traces of flight (Volichnia), probing marks, and tracks showing morphology similar to modern shorebirds (G. dominguensis), strongly suggest an avian affinity for the producers of the fossil tracks and, in consequence, the Santo Domingo track site would be younger than supposed”.

Now, Richard Melchor, one of the original researchers, along with two scientists from Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, have re-dated the rocks using a different radioactive dating method – 206Pb/238U. The rock formation has now been classified as Late Eocene, 37 million years old. They concluded: “In consequence, the mentioned tracks are assigned to birds and its occurrence matches the known fossil record of Aves”. (Aves are birds.)

Melchor and one of his original colleagues have now formally retracted their original 2002 report with the comment: “Recent radiometric dating of the sedimentary sequence containing these bird-like footprints (renamed as the Laguna Brava Formation) indicated a Late Eocene age. Further geological studies suggest that the region suffered a complex deformation during the Andean orogeny, including block rotation. In consequence, our previous inferences about the possible implications of this finding for the fossil record of Aves are no longer supported”.

Editorial Comment: Did you notice that by substituting one method for another the evolutionists have managed to off-load 175 million years and bring the prints back into line with current evolutionary theory on bird origins?

When we looked up the references given for re-dating the rocks, we found yet another reason to doubt all evolutionary dates for these rocks. According to an article in Tectonophysics vol. 583, pp105–123, 11 January 2013: “the Laguna Brava Formation would have been deposited during the Late Eocene with a mean sedimentation rate of about 1.4 cm per thousand years, probably in relation to the onset of the Andean deformation”. A sedimentation rate of 1.4 cm (0.55in) per thousand years is 0.014 mm per year – about the thickness of one grain of silt per year. The layer in the formation that was used for the radioactive dating certainly wasn’t laid down at this slow pace. It consisted of tuff – a volcanic ash that is turned to rock. Volcanoes don’t do slow! Furthermore, the layers in the formation that contain the actual foot prints had to be soft wet mud of sufficient thickness for the birds to leave impressions. It then had to be covered up much more quickly than 0.014mm per year in order to preserve the prints.

So, let’s summarise this interesting sequence of dating events: In 2002 bird-like tracks are reported, but because the rocks are dated as 212 million years the tracks are classified as dinosaurs. By 2009 careful study of the prints shows they are definitely birds, and therefore the rocks should be younger. In 2013 the rocks are re-dated to 37 million years to prove they were young enough to have bird prints in them, and the story now fits the authorised version. This should serve as a cautionary tale for any who believe radioactive dating gives us absolute ages for rocks, and that fossils support a proven evolutionary timetable.

And don’t forget to check out another footprint problem, where a print that looked like a dinosaur was classified as a giant bird because the rocks it was found in were considered too young for dinosaurs. See our report “Bird-not-a-saurus” here. (Ref. chronology, fossilisation)

Evidence News, 6 November 2013

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