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Validating Darwin with Radiometric Dating

Engraving of Charles Robert Darwin (1809-1882).  February 12, 2009, marks the 200th anniversary of his birth.

According to a recent article published in Science, the Colorado River began to cut its course through the Grand Canyon 17 million years ago.  The authors base their claim on radiometric dating of cave formations found in the canyon walls.

• Polyak, V.; Hill, C.; Asmerom, Y. Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table-Type Speleotherms. Science 2008, 319, 1377-1380.

Their method, a type of radiometric dating called uranium-lead (U-Pb) dating, relies on the fact that uranium isotopes radioactively decay to form lead isotopes.  By comparing the amount of each isotope in a sample, the age of the sample can be calculated.¹

Radiometric dating not only supports the geologic "evolution" of the Grand Canyon, it validates a central tenet in a much different theory of evolution - a theory introduced by Charles Robert Darwin in his 1859 publication, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life:

• "I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species.  Furthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification."²

An important criticism of Darwin's theory of evolution was its requirement for "an almost infinite number of generations", when evidence at the time suggested earth was less than 100 million years old.  Nearly 50 years after Darwin published On the Origin of Species, research on radioactive elements in rocks provided the first reliable evidence that the earth was old enough to accommodate the evolution of complex organisms.  In 1907, Bertram Boltwood published an article describing a novel, radiometric method for determining the age of minerals - a method he used to date a rock sample at more than 2 billion years:

• "Knowing the rate of disintegration of uranium, it would be possible to calculate the time required for the production of the proportions of lead found in the different uranium minerals, or in other words the ages of the minerals."³

Boltwood's method is conceptually similar to the dating method used by Clair Patterson in 1956 to determine the currently accepted age of the earth.⁴  Darwin would likely agree that Patterson's calculation of 4.55 billion years satisfies evolution's requirement for a "vast lapse of time".²

You can use SciFinder or STN to search the CAS databases for additional information about radiometric dating and evolution.  If your organization is enabled to use the web version of SciFinder, you can click the links in this article to directly access details of the cited references.

Contributed by
Peter S. Carlton, Ph.D.
CAS Communications

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References

1. U.S. Geological Survey. http://www.usgs.gov/ (accessed February 10, 2009).
2. Darwin, C. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, 1st Edition; John Murray: London, 1859.
3. Boltwood, B.B. On the Ultimate Disintegration Products of the Radioactive Elements. Am. J. Sci. 1907, 23, 77-88.
4. Patterson, C. Age of Meteorites and the Earth. Geochim. Cosmochim. Ac. 1956, 10, 230-237.

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