INCREMENTAL EVOLUTION OF THE AGE OF THE EARTH

Arthur Holmes taught geology at Durham University from 1924 to 1943. He gave students “regular updates on the age of the Earth, announcing with exaggerated gravity, ‘Today the age of the Earth is …’ “(Lewis, 2000, p. 140).

20^th century literature conveys what Holmes implied: the age of the Earth is a movable benchmark; expected movement probably will increase that age; technical advances may imply that a final value for the age of the Earth has been reached.

In (1962-1963), I studied the age of the Earth, with help in probability from a fellow graduate student, Bert Fristedt, who now is an active Emeritus Professor of mathematics at the University of Minnesota. The 1962-1963 work survives as two abstracts, one in Trans. AGU, v.45, p.117, 1964, which says in part, “A historical survey indicates that the age of the oldest accepted radioactive mineral has increased, on average, by 450 m.y. per decade over the past 50 years. This rate of increase has been relatively constant and is not now decreasing.”

The line developed in 1964 is: y = 450x + 225, where y is the age in m.y. of the oldest accepted mineral date, and x is the date of publication, measured in decades from AD1900. The x is historical time, with zero at the time radioactivity was discovered. The constant in the equation, 225, has units of m.y. and a magnitude similar to values for hour-glass methods (ocean salinity, sediment thickness) that competed with early radioactivity methods.

Since 1964, three dates on zircons from Western Australia exceed prior ages of oldest minerals. These three are (with reported zircon age, publication date in Nature, and first author): 4150m.y., 18 Aug 1983, D.O.Froude; 4300m.y., 19 June 1986, W.Compston; and about 4400m.y., 11 Jan 2001, S.A Wilde.

The Western Australia zircons test the 1964 prediction with minerals analyzed two decades after the 1964 line. The first two sets of zircons plot 4% and 5% above the 1964 line. The third set plots 9.2% under the 1964 line. The first date elicited evidence suggesting that it might not be ‘accepted’ (Scharer and Allegre, 2 May and 10 Oct 1985).

The incremental evolution of the age of the oldest mineral resembles other incremental evolutions for such disparate scientific benchmarks as charge of an electron (R.P.Feynman, 1985), Hubble Constant (Virginia Trimble, 1996, Fig 1) and eustatic rise of sea level predicted for AD2100.