[Published in Fortean Times, no. 68, April/May 1993, p. 65.]

Radiometric Dating

I was quite disappointed to see Richard Milton's highly misleading article on radiometric dating [FT66:24]. Milton relies, uncritically, on the work of Mormon creationist Melvin Cook and on Henry Morris, President of the Institute for Creation Research. It appears that he has not consulted the original sources he cites. For instance, he claims that Hans Petterson estimated the rate of meteoritic dust fall on the earth's surface to be 14 million tons per year, but Petterson himself considered this to be an overestimate and suggested a figure of five million to be more accurate. His measurement, done in 1960, was performed with smog measurement devices at the summit of Hawaii's Mauna Loa volcano. In the 33 years since those measurements, accumulated satellite data show the actual rate of meteoric dust fall to be 11,000 to 18,000 tons per annum. Milton's information is not only out of date, but inflated more than 700 times.

Milton brings up discordant potassium-argon dates on Hawaiian lava flows, but fails to note that the very sources he cites explain that the inaccurate dates are caused by the presence of olivine xenoliths, which carry less argon. This is the sort of thing that is allowed for in radiometric dating. To cite Funkhouser and Naughton's 1968 study of xenoliths as evidence against the general accuracy of potassium-argon dating is simply dishonest.

Finally, Milton wrongly claims that "the sole method [...] of arriving at this immense age [of the Earth] is radiometric dating." He not only overlooks the fact that there are independent and self-checking radiometric techniques (isochron dating), but he ignores non-radiometric techniques such as ice-core dating, palaeometric [magnetic?] reversal data, geologic data (such as varves) and dendrochronology (tree-ring dating). Dates from all of these techniques converge, confirming the general accuracy of radiometric dating.

For a history of different methods of dating the Earth and discussion of the misguided objections Milton raises, I recommend G. Brent Dalrymple's recent book, The Age of the Earth and Arthur N. Strahler's Science and Earth History.

Jim Lippard
Tucson, Arizona

[Milton replies in a letter in Fortean Times #69, June/July 1993, p. 64, as does a Paul Garner whose reply has nothing to do with radiometric dating.]