NOTE: Austin has promised to publish all of his data at some point, and this work cannot really be completed until that happens.
The Grand Canyon looks something like this:
Grand Plateau Canyon \ ________________ _\ /________________ __| /_________________ ___\ /__________________ <-- Paleozoic rocks ____| |___________________ _____\__/ ___________________ ...\ \ \ \ \ \ .... <-- Angular unconformity .....\ \ \ \ \ ...... .......\ \ \ ............ .........\ .................. <-- Metamorphic rocks
Steve Austin of the ICR wrote Impact #224, claiming that he has derived a Rb/Sr isochron age for lava flows on the Uinkaret Plateau in excess of 1.3 billion years (several of these flows spill into the canyon). The Cardenas Formation, a tilted layer at the bottom of the canyon (below the angular unconformity) is generally accepted as being about 1.1 billion years in age.
Clearly, something is wrong here. Lava flows which spill off the plateau into the canyon cannot be older than the canyon itself. The canyon can't be older than the rocks that it is cut into. The flat sediments can't be older than those below the angular unconformity (as they were deposited on top).
Austin's apparent thesis: Rb/Sr dating of the feature which must be the youngest gives a value older than that which must be the oldest, therefore the method does not work. (Of course, then, all radiometric results can safely be ignored.)
I received a description of the data from Steve Austin (a little more than what was published in Impact, but not nearly enough to really know what is going on, unfortunately). I forwarded the data to Dr. G. Brent Dalrymple of the U.S. Geological Survey. He has apparently received many questions on Austin's work, and sent me a short article that he had written on the subject. I am in the process of getting permission to give out copies of this report; please send contact me ([email protected]) if you are interested in getting a copy (I can probably get copying done for free, but you may have to cover the postage).
A few excerpts:
"Trying to prove that some methodology does not work by focusing on a small percentage of anomalous data, while ignoring a much larger percentage of concordant data is not a productive exercise because it will prove nothing except that the method did not work in those particular instances [underlined in original -CS]. It is even less meaningful if one seeks to perform an experiment under circumstances that are known beforehand to be inappropriate, and this is precisely what Steven Austin is doing. He has set up an experiment that will fail because he has chosen circumstances that guarantee the outcome. So what is being tested--radiometric dating methods or Steve Austin's knowledge and objectivity?"Commenting on the fact that Austin has published three different alleged isochron dates for the Cenozoic lava flows:
"These differences [changes in various measurements for certain samples! -CS] explain the change in Steven's ``isochron age'' from 2.07 Ga to 1.39 Ga (or vice versa), but we do not know why the analytical data changed so radically from one table (and one diagram) to the other, why one sample was omitted from the second table, or why Steven selects just a few of the many available hawaiite flows for his project."Summary:
"In summary, I can't really tell what Steven Austin is doing with his western Grand Canyon data. They keep changing and he never provides enough information to do an independent evaluation of important things like the isochron fit. In addition, he is ignoring what I and others have told him about using lava flows that are demonstrably not cogenetic, and he is ignoring Leeman's data, which clearly indicates that the rough correlation between the Rb and Sr isotopic ratios reflects time- integrated radioactive decay in the source rock(s), and not in the lava flows."
David M.V. Utidjian asks:
But isn't the K-Ar method of radiometric dating the apropriate method for dating igneous rocks like lava flows? Please correct me if I am wrong.
The K-Ar dating method is probably the most popular method for dating lava flows. Since it involves relatively few measurements, and they are relatively straightforward, it is also one of the cheapest methods. Jim Lippard was kind enough to look up and copy for me a technical paper on the topic of K-Ar dating the Grand Canyon lava flows (McKee et. al, 1968). It gives K-Ar dates for laval flows associated with the Toroweap fault (~1.2 million years). Austin references this paper (Austin, 1992, 1988), so it seems that these are the same flows that he is "dating."
Despite its popularity, the K-Ar method is not the most reliable dating method. Since it is not an isochron method, there is no built-in check for contamination (that is, in the event of contamination it will yield an incorrect date -- while an isochron method under the same conditions will usually yield no date at all). Since argon is an inert gas, later heating events can permit it to escape, and partially or completely reset the "clock." Since there is excess argon associated with the lava source, its method of cooling must be such that the initial argon could escape.
This does not mean that the K-Ar method is useless; it only means that it must be used with caution -- on samples that have the right sort of history and properties. In fact, this case (plateau lava flows) appears to be one where K-Ar yields the right age and proper use of Rb/Sr dating yields no age at all.
If we plot all of the Rb/Sr data which Austin has ever published (in three different places) for "Western Grand Canyon" lava flows, you will see why I say "no age at all":
Sr-87/Sr-86 | (5) 0.711 + ===== 0.708 + | | (D) 0.707 + (4) (f) | (C) | 0.706 + (3) | | 0.705 + (2) (e) | (1) (d) | 0.704 + (b) | (c) | (B) 0.703 + (Aa) | | 0.702 +-------+-------+-------+-------+-------+-------+-------+-------+ 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Rb-87/Sr-86
Lowercase letters (e.g., "(a)") are from Austin 1988. Uppercase letters (e.g., "(A)") are from Austin, No Date. Numbers (e.g., "(1)") are from Austin, 1992. Warning: All data points were "eyeballed" from published diagrams. ["(Aa)" is "(A)" and "(a)" relatively close together.]
In Austin's diagrams, A-B-C-D fall relatively close to a line. a-b-c-d-e-f also fall relatively close to a line. 1-2-3-4-5-6 fit very well to a single line. However, you can see that there is quite a bit of scatter when all of the data is plotted together.
I've been told that Austin has in the past used a computer program that discards data that do not lie near a line. If that is what he is doing here (it has that appearance, but I really don't have enough information to be sure), it is no surprise that he is ending up with data points that fall on or near a line.
It is also no surprise that the resulting "age" is not meaningful. In ignoring data points away from the line, one would be ignoring data points which indicate that the "line" does not represent an isochron. Here are two reasons why there is the appearance that this is what is going on:
In Austin 1988 (lowercase letters above), he presents data from Leeman, 1974. He uses samples "U-33, U-35, U-59, U-24, U-43, and U-58." He does not explain why he chooses only these data points. Leeman's diagram shows considerable scatter to the data. From Leeman's diagram, it is clear that no Rb/Sr age can be calculated. Austin has chosen only a few of the data points, and these happen to fall near a line (however, the appearance is that even these are not close enough to a line to be considered a valid isochron date).
For another example, the most recent data (Austin, 1992) appears in two forms. In an as-yet-unpublished paper (maybe a chapter from a forthcoming book), Austin produces an isochron that gives an "age" of 2.07 Ga, from samples "QU-1, QU-2, QU-3, and QU-5."
In a report on the progress of the "Grand Canyon Research Project," Austin notes that there was a problem with some of the measurements, that an incorrect value resulted, but that the sample is now correctly dated. (The project is running a little behind for this reason.)
The Impact article uses the some of the same sample numbers as the other isochron, however (as Dalrymple notes) some of the isotope concentration values have changed. (I suspect that this is a result of the correction of the lab results.) However, the Impact isochron uses samples "QU-1, QU-2, QU-5 and QU-14." Sample QU-3 is missing. Its previous position would be well off the line.
Only ICR folks know why sample QU-3 was dropped, why sample QU-4 has never been used, and where samples QU-6 through QU-13 are. Until they publish all of the lab results and all of the data points, it will be difficult to assess exactly what has been going on.
The appearance at the moment is that their results are not the major blow against isochron methods that they are claiming. Until they are more open with their results (ALL of their results), that will have to suffice.
David M.V. Utidjian asks:
It also appears that K-Ar methods would be more accurate for the apparent ages of these samples than the Rb-Sr method because the of their respective halflives of 1.25 x 10^9 for K-Ar and 4.88 x 10^10 for Rb-Sr, respectively. That is to say the error bars for the Rb-Sr method may be an order of magnitude larger than the ones for the K-Ar method in my amateur evaluation of the two techniques.It is true that the decay rate has some influence on the size of the errors. However, the disagreement in this case cannot be explained merely by measurement error. It is still important to understand where the two methods agree or do not agree (and why).
Austin, Steve, 1992, "Excessively Old ``Ages'' For Grand Canyon Lava Flows", Impact, Number 224, February.
Austin, Steve, 1988, "Grand Canyon lava flows: A survey of isotope dating methods", Impact, Number 178, April.
Austin, Steve, No Date, "Grand Canyon dating project: A proposal for research".
Leeman, 1974, "Late Cenozoic Alkali-Rich Basalt from the Western Grand Canyon Area, Utah and Arizona: Isotopic Composition of Strontium", in Geological Society of America Bulletin, Vol. 85, November, pp. 1691-1696.
McKee, E., D., et al., 1968, "K-Ar Age of Lava Dam in Grand Canyon", in Geological Society of America Bulletin, Vol. 79, January, pp. 133-136.