Joined: Feb. 2005
|Quote (Scienthuse @ Sep. 30 2009,23:36)|
|Or perhaps we might talk a bit about your presumptive philosophy which thinks it lays claim to all operational science, by assuming that all lead 206 in the entire world is a complete result of the U 238 decay chain. This is entirely presumptive on your part. And you ignore at the same time the helium inside, which most of it should have long dissipated if the earth is 4.6 billion|
Looks as if you don't know much about radiometric dating.
No real geologist presumes that all the 206Pb that we see is the result of the decay of 238U, at least after the solar system formed. Lead in troilite in the Canyon Diablo meteorite is thought to contain the primordial proportion of lead isotopes (and is thought to be so for good reason). The isotope relevant isotope ratios for this material are:
206Pb/204Pb 207Pb/204Pb 208Pb/204Pb 238U/204Pb
9.46 10.34 29.44 0.025
(Patterson, C., H. Brown, G. Tilton, and M. Inghram, 1953, Phys. Rev., v. 92, p. 1234; and Patterson, C., 1955, Geochim. et Cosmochim. Acta, v. 7, p. 151.)
I'm sure you can see the significance of these ratios, being such an expert and all that.
There are actually quite a few studies of dating using helium daughter product, starting with the first radiometric date by Rutherford in 1905. For example, http://www.geotrack.com.au/uthhe/u-th-he-flier.htm, http://bgc.org/facilities/u_th_he_lab.html, and http://www.sciencemag.org/cgi/content/abstract/sci;196/4287/291.
I suppose that by "you ignore at the same time the helium inside" you are referring to the RATE group's study of zircons. That's been extensively discussed. My conclusion is that they may possibly have found an interesting anomaly, but they are far from having enough data to establish the validity of their methods and claims. They need to study a much wider variety of zircons, especially some with a simpler thermal history and no possible exposure to helium compared to the few zircon studies they published. They also need to justify their large extrapolations of diffusion data.
Since they have not published anything on this subject since 2004, and there's not even a hint of any further work going on, it looks to me as if they gathered enough data to provide a sciency-sounding reference for the sheeple and don't intend to go any further.
If you have any actual, you know, evidence that you know what you're talking about and you're not so "green and tender", especially any evidence that scientists assume that "all lead 206 in the entire world is a complete result of the U 238 decay chain" or any evidence that the RATE group's claims are worth further investigation, trot it out.