T_aquaticus,
PaulGiem:
Perhaps the easiest way one can see how the dates could be identical but misleading is to suppose that one starts out with 2 magmas, A and B. One ages them. One then mixes them in various proportions, and obtains “isochron” lines that are actually mixing lines.
That doesn’t work for U/Pb concordia/discordia dating. The initial ratio of the two different U isotopes doesn’t matter, and nearly all of the Pb is excluded during zircon formation.
The initial ratio of the two different U isotopes is always constant, or perhaps better, predictable (it does change with time), except at the Oklo formation (depleted in U-235)—otherwise uranium mines would be rated for their U-235 percentage. That means we reasonably know the initial ratio.
You are making the assumption that zircon formation is at the same time as the last time a given magma was melted, which is probably incorrect, as inherited zircon age is a known problem. Thus, since zircons have an especially high melting point and may still be solid in a magma, a date on a zircon is not necessarily the date the magma was last cooled from a hot slurry. Don’t believe me? just ask N. H. Gale: “The dating of plutonic events.” In Odin GS (ed): Numerical Dating in Stratigraphy. Chinchester, UK: John Wiley and Sons, 1982, pp. 441-50:
Even though, [sic] a zircon suite may be well-dated by the U-Pb discordia method . . . , there can still be doubt whether this date is that of the rock formation itself or whether the zircons are detrital or have inherited radiogenic lead, resulting in the U-Pb result giving an ‘age’ older than the rock formation. (This danger is also inherent in fission track ages of zircons from bentonites.)[pp 446-7]
You say,
Ar boils out of the lava before it solidifies, so it doesn’t matter how much Ar is present in the magma to begin with.
We already know that substantial amounts of argon can be retained if the lava flow is under water. So it is of interest that the Columbia basalt has pillow lava at its edges. And remember that even lava that flows under air retains some argon. It just is sometimes able to be subtracted out because its isotopic composition matches that of modern air argon.
You say,
And yet, all of these methods agree with one another across different labs and different minerals.
I’m looking for blinded tests, with all data reported. Maybe my suspicions are wrong, and I will have to reassess my present position. But every time someone states that we have enough data and shouldn’t try something that in medicine would be absolutely required, my suspicions deepen. Just do the tests.
We’ve covered this before, but I’ll try again. When I read of argon leakage to explain low K/Ar dates, and argon retention to explain high ones, sometimes applied inconsistently (for example, the concern over phenocrysts in lava in Dalrymple 1969, then the rejection of glass dates in favor of phenocryst dates in Maniken and Dalrymple 1972 [“Electron microprobe evaluation of terrestial basalts for whole-rock K-Ar dating.” Earth Planet Sci Lett 17:89-94—In one case the glass in question was unaltered, and still gave a potassium/ argon age of 1.6 million years rather than 7.4 million years]), and knowing that in many rocks we can get 3 or 4 different K/Ar dates (don’t get me started on Ar/Ar dates), and realizing that both high (more often) and negative (much less often) Rb/Sr dates can be obtained and then written off without further proof as mixing lines without anyone asking whether the same could be said for “good” dates, and finally when U/Pb dates (see below) are mostly discordant, I really want concordance with blinded dates before I can feel comfortable accepting radiometric dating at face value. If you’re really that confident that radiometric dating is valid, just do it. If not, maybe I shouldn’t be confident either.
There is one other caveat. It would be best if we select samples that have not yet been dated, both to avoid selecting previously reported matching data, and to avoid previously selected non-matching data. The Cardenas basalt in the Grand Canyon, for example, is known to be non-matching and should not be used.
You say,
Where is the evidence that the two U/Pb ratios do not agree with one another most of the time? What is the amount of disagreement?
It is not often realized that the very fact that U-238/Pb-206 and U-235/Pb-207 ratios are not on the concordia line means that the model dates do not match. If they did, the ratios would plot on the concordia line. That’s what the concordia line means; it is where the dates are concordant. (It is, BTW, not a straight line.)
You ask what the amount of disagreement is. That depends on the specific data. The data in Wikipedia ( https://en.wikipedia.org/wiki/Uranium–lead_dating ) isn’t that far off of the concordia line, just meaning somewhere between 10 and 20 million years discordance(out of some 220 million years) for the lower data point, and the upper data point virtually matches the concordia line. I have seen other data that can differ by close to 50%. (See slide 10 of https://websites.pmc.ucsc.edu/~pkoch/EART_110A/Lectures/L4%20Time&Tectonics.pdf , the lower sample, although this data may be artificial.)
But perhaps more important is the interpretation such data are given. Rather than simply giving 3 dates with, say, 220, 410, and 455 Ma, what is done is a discordia line is drawn and the intercepts are assigned a geological meaning, in the case of the wikipedia data ~50 Ma for the lower intercept and 461.17 ± 0.31 Ma. So that 220 or 230 Ma date is actually off by some 170 or 230 Ma, depending on whether the lower or upper intercept is more important.
From your quote:
and that many submarine basalts are not suitable for potassium-argon dating.
Why not “all submarine basalts are not suitable”? How can we distinguish the “good” from the “bad” before we run the date?
You say,
This is why they don’t use rocks that have xenocrysts in them.
But note the two-step above with phenocrysts.
You say,
What’s wrong with the studies that have already been done?
They’re not blinded, and I don’t know that all results have been reported.
Once again, if it is a field wide conspiracy of throwing out dates people don’t like then it is a simple matter of measuring those same rocks. Accusing scientists of fudging their data requires some actual evidence.
Again, you are missing the concerning thought process. The scientists don’t set out to fudge their data. It is just that they “know” the date they are supposed to get, and discordant data are attributed to some flaw in the sample and are possibly viewed as not worth reporting (positive results in any field are easier to publish than negative ones, and both are easier to publish than chaotic ones). You don’t have to invoke a grand conspiracy.
Again, maybe I’m barking up the wrong tree. But if so, it should be easy to prove.
RonSewell (C98),
The Existence of Carbon-14 in Very Old Fossil Material
… beyond that we are at an impasse at present.
I would agree that we don’t have “proof”, although there are other considerations that I will outline in the thread on radiocarbon in coal (again, if I am permitted).
But there are experiments that can help to further differentiate between the 2 major possibilities. And I plan to help get them done.
Errors in the Calibration Curve in the Historical Era
… For one, the earliest specific date which seems to enjoy universal recognition seems to be 690 BC with Sennacherib’s engagement with Hezekiah and Taharqa.
You may know that the argument under this heading lead to an article which is referenced near the end of C46, and therefore will not be repeated here (the computer tries to discourage multiple links to the same address in one thread). I just found out this last week that there is allegedly a similar problem in Jerusalem, although I do not know enough details yet (but am eagerly trying to find out). Do you have any actual radiocarbon data for the Sennacherib/Hezekiah/Taharqa connection, with a reference? It could have a bearing on our other data.
Zero missing rings over a millennium serves to validate confidence in the tree ring chronologies, and I am unable to find a creationist response.
My personal response is that this is what I expected. The Carbon-14 calibration curve has been validated IMO back to about 336 BC. So consilience at AD 744 would be expected in the theory I presently find most attractive.
Given that you do not seem to be a fan of speeded up decay, and that the tree ring / 14C conscilience is well supported, it appears to me that of the options you lay out in the article, that an ancient flood, constant decay model is the only one consistent with this scope of evidence.
I’m not so sure we can close the books on this question (partly because of the Nineveh bones apparent success), but you could be right. If I find enough data that supports the ancient flood, constant decay theory against the others, I will agree with that theory.
). Science is supposed to be arranged so that the only true authorities are observation, that is supposed to be reproducible, and logic, which anyone sufficiently intelligent can see. Authorities in science are authoritative precisely because they are transparent. Any hint of non-transparency makes that person less authoritative. (That is probably why science has resisted postmodernism so long; science does not encourage constructing your own truth.)