Claim CD013:
Potassium-argon dating of rocks from lava flows known to be modern
gave ages millions to billions of years older.
Source:
Morris, Henry M., 1974. Scientific Creationism, Green Forest, AR: Master
Books, pp. 146-147.
Response:
- Argon may be incorporated with potassium at time of formation. This is
a real problem, but it is easily overcome either by careful selection
of the material being dated or by using 40Ar/39Ar
dating instead of K-Ar dating.
In the case of the claim about recent lava yielding dates that are
millions to billions of years old, H. M. Morris (1974) misstated the
facts concerning these "anomalous" dates as published in Funkhouser and
Naughton (1968). The main misstatements of fact by Morris are as
follows:
- It was not the lava that was dated, but inclusions of olivine,
called "xenoliths", present within the lava. These gave anomalously
old age because they contained excess argon that the enclosing lava
did not.
- Morris failed to mention that the lava matrix without the
xenoliths was dated and found to be too young to date using
potassium-argon. (Funkhouser and Naughton [1968, 4603], stated that
the matrix rock "can be said to contain no measurable radiogenic
argon within experimental error.") This is consistent with the
recent age of lavas and the state of the art of K-Ar dating at that
time. The presence of excess argon was only a problem for the
xenoliths but not for the lava containing them.
Morris cited other examples of anomalous dates produced by excess argon
and falsely claimed that it is a universal problem for K-Ar dating. The
problem is not universal, as the majority of minerals and rocks dated
by K-Ar do not contain the excess argon. Where excess argon is a
problem, accurate, reliable dates typically can be obtained using
40Ar/39Ar dating, as demonstrated by Dalrymple
(1969) and Renne et al. (1997) and discussed by Dalyrmple (2000).
- Morris's complaints are dated in that, for the most part, geologists no
longer use the K-Ar dating technique as was practiced in 1974.
Instead, K-Ar dating has been largely replaced by the related
40Ar/39Ar dating technique. This change also
solved other problems that Morris complained about in his discussion of
the K-Ar dating technique. These complaints were as follows:
- Claim: K-Ar dating techniques must be calibrated by uranium-lead
(U-Pb) dating.
Response: Some calibrations between U-Pb and K-Ar were done in the
1940s and early 1950s, but the decay rates of all the different
radioisotopes involved are now known to within 1 percent, making
the different dating techniques independent.
With 40Ar/39Ar dating, it is possible to
calibrate this dating method by using volcanic deposits created in
historic volcanic eruptions -- for example, the eruption of Mount
Vesuvius on August 24, 79 C.E. (Renne et al. 1997). In addition,
40Ar/39Ar dating can be compared not only
with U-Pb dating techniques but also with other absolute dating
techniques -- for example, K-Ar, Rb-Sr, and Sm-Nd dating techniques
-- which all provide dates consistent with each other and with
associated 40Ar/39Ar dates. This has been
demonstrated by the dating of chondrite meteorites (Dalrymple 1991)
and tektites and other ejecta and deposits created by the giant
meteorite impact at Chicxulub in the Yucatan Peninsula (Dalrymple
et al. 1993).
- Claim: The potassium-argon is an open system.
Response: The papers cited by Morris fail to probe this point. The
first paper simply demonstrates that rock altered by weathering
cannot be dated. This is a common-sense conclusion understood by
geologists literate in the basics of their profession; it is
irrelevant to the unaltered minerals that are typically
dated using K-Ar, 40Ar/39Ar, and other
techniques. The final paper claims potassium is quite mobile
because potassium can be extracted from iron meteorites by using
distilled water. However, K-Ar dating commonly uses potassium
silicate minerals, which are very insoluble in water and resist
weathering. Potassium cannot be significantly leached from the
minerals used in K-Ar dating, or, conversely, the minerals from
which significant potassium can be leached are not the minerals
used in K-Ar dating.
- Claim: The decay rate of potassium is subject to
change.
Response: This is simply not true.
- Claim: Argon maybe incorporated with potassium at time of
formation.
Response: See first point (a) above.
- Claim: K-Ar ages are extremely variable.
Response: As previously noted, K-Ar and
40Ar/39Ar dating both provide extremely
consistent dates when the methods are used properly (Dalrymple
1991; 2000). The single paper (Engels 1971) cited by Morris
clearly stated that variability resulted from presence of unwanted
impurities in the specific mineral being dated. If the sample
dated consisted of an absolutely pure mineral, there would not be
any variability in the K-Ar dates obtained from them.
Links:
harlequin2, 2001. Ar-Ar dating assumes there is no excess argon?
http://members.cox.net/ardipithecus/evol/lies/lie024.html
harlequin2, 2001. 200 year old lava dated 2.96 billion years old?
http://members.cox.net/ardipithecus/evol/lies/lie023.html
Lindsay, Don, 2000. Fresh lava dated as 22 million years old.
http://www.don-lindsay-archive.org/creation/hawaii.html
Stassen, Chris, 1999 (Jan.). Feedback response.
http://www.talkorigins.org/origins/feedback/jan99.html
(4th response
down)
References:
- Dalrymple, G. Brent, 1969. 40Ar/36Ar analyses of
historic lava flows. Earth and Planetary Science Letters 6: 47-55.
- Dalrymple, G. Brent, 1991. The Age of the Earth. Stanford, CA:
Stanford University Press.
- Dalrymple, G. Brent, 2000 (May/Jun). Radiometric dating does work!
Some examples and a critique of a failed creationist strategy. Reports
of the National Center for Science Education
20(3): 14-17.
http://www.ncseweb.org/resources/rncse_content/vol20/6061_radiometeric_dating_does_work_12_30_1899.asp
- Dalrymple, G. B., G. A. Izett, L. W. Snee and J. D. Obradovich, 1993.
40Ar/39Ar age spectra and total-fusion ages of
tektites from Cretaceous-Tertiary boundary sedimentary rocks in the
Beloc formation, Haiti. United States Geological Survey Bulletin
no. 2065.
- Engels, J. C., 1971. Effects of sample purity on discordant mineral
ages found in K-Ar dating. Journal of Geology 79: 609-616.
- Funkhouser, J. G. and J. J. Naughton, 1968. Radiogenic helium and
argon in ultramafic inclusions from Hawaii. Journal of Geophysical
Research 73(14): 4601-4607.
- Morris, 1974. (see above.)
- Renne, P. R., W. D. Sharp, A. L. Deino, G. Orsi and L. Civetta, 1997.
40Ar/39Ar dating into the historical realm:
Calibration against Pliny the Younger. Science 277: 1279-1280.
Further Reading:
Attendorn, H.-G. and R. N. C. Bowen, 1997. Radioactive
and Stable Isotope Geology. London: Chapman & Hall.
Faure, G., 1986. Principles of Isotope Geology, 2nd ed. New York:
Wiley.
McDougall, I. and T. M. Harrison, 1988. Geochronology and
Thermochronology by the 40Ar/39Ar Method. Oxford Monographs on Geology
and Geophysics no.9. New York: Oxford. (technical)
Thompson, Timothy, 2003. A radiometric dating resource list.
http://www.tim-thompson.com/radiometric.html
Wiens, Roger C., 1994, 2002. Radiometric dating: A Christian perspective.
http://www.asa3.org/ASA/resources/Wiens.html
created 2003-6-9, modified 2004-9-21