Wow. That was fast. I got my free PDF copy of Evernden
et al. by email this morning. I think I'm gonna like interlibrary loan!
Creation moonbat website claimed:
On pages 171-174 they discuss why all but one potassium/argon date for the Rusinga Island bioites was discarded. Yet they use biotite in an uncritical manor in other areas where the dates they obtained matched their expectations.
I will be quoting directly form Evernden
et al.; I am assuming that the amount quoted will lie within fair use standards.
Evernden et al., p. 172:
The potassium-argon results obtained on biotite samplescollected from the tuffaceous sediments of Rusinga Island are highly variable.
In other words, rather than hiding a problem, they are admitting it to the world that obtaining reliable dates is difficult.
Evernden et al., p. 172:
These detrital sediments lie upon a Precambrian surface and may be expected to contain significant fractions of Precambrian biotite.
[Bolding added.]
On other words, the problem is contamination with far older material. If YEC were true, the Precambrian material would not be very old, and so the contamination would not have led to
older dates. It is because the Precambrian material is so old that this problem is occurring.
Evernden et al., p. 172:
If such occurs, widely variable K-A dates may result with the minimum age yielding the best estimate of the age of the deposits. If the sample yielding the the minimum age has characteristics that reduce the possiblilty of contamination, we can accept the figure obtained from it as a close estimate of the true age of the deposit.
[Bolding is added.]
In other words, it's not a question of choosing the one date that "matches expectations". The best date will be the youngest, and there is no guarantee that this one is going to match "expectations".
Evernden et al., p. 172, 174:
The sample used for KA 336 was composed of large (1/2" diameter) euhedral biotite books collected from tuffaceous sediments at the site R 107 in the Kiahera Series. This site is stratigraphically below most fossil-vertebrate localities on Rusinga Island. All other determinations were made on fine-grained biotite concentrated from tuffaceous sediments, all of which might have appreciable contaminating components. The obtained argon-potassium "ages" indicate high contamination: KA 656 -- 22.2 million years, KA 800 -- 42.0 million years, KA 801 -- 167 million years, KA 802 -- 107 million years.
Thus our best estimate for the age of the deposits on Rusinga Island is that of KA 336, that is, 15.3 ± 1.5 × 106 years, an age equivalent to the Barstovian of North America. The fossil evidence from these deposits does not appear to contradict this age.
[Bolding is added.]
In other words, we actually see a large spread of ages. The "best" age was not chosen, rather, it was determined that the "best" age would be the youngest, and it still might have been older that the fossil evidence would have indicated.
The youngest sample was examined, it was determined that contamination from
the un-YEC ancient Precambrian was less likely, and, indeed, the it was close to the age suggested by the fossil evidence, ages that were determined elsewhere by more reliable means.
So, everything seems on the up and up. I certainly see no signs that problems are being hidden or brushed under the rug. Their procedure is explained, the data is given, and anyone anywhere can look at this paper and make up their own minds as to the reasoning of the authors.
Edited by Chiroptera, : added subtitle
Actually, if their god makes better pancakes, I'm totally switching sides. --
Charley the Australopithecine
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