A slim but useful and interesting volume of the history of attempts to determine the age of the Earth. Author Patrick Wyse Jackson is curator of the Geology Museum at Trinity College, and therefore has a special fondness for Irish chronologists. He starts with a quick summary of Egyptian, Mesopotamian, and other ancient civilizations’ attempts to come up with an age, then quickly goes to the Biblical chronologies, focusing, of course on Archbishop James Ussher and his date of October 23, 4004 BCE. (Jackson debunks the myth that Ussher went so far as to set on 09:30 AM for the Creation; that time was hit on by John Lightfoot eight years before, and it was Lightfoot’s estimate for the creation of Man, not the Earth). Ussher actually set his date as the autumnal equinox in Julian Year 710; I suppose you could figure out an exact time for the equinox, although what an equinox would be before the creation of the Sun is unclear. However, archeologists routinely use what’s called the Proleptic Julian Calendar when trying to affix dates to events before the use of the real Julian Calendar – i.e., running the Julian Calendar backward to a date before it was actually used. You could therefore do the same thing with a “proleptic sun”, and a little messing around with astronomy software shows that the autumnal equinox was actually at 13:11 (Jerusalem time) on October 22 in 4004 BCE. And the First Point of Aries was just a little west of 44 Ophiuchi. Close enough for government work.


The onset of geology quickly showed that you just couldn’t fit all that rock into 6000 years, and Jackson covers the speculations of Lyell, Hutton and other early rock-hammerers. Serious estimation attempts included trying to establish sedimentary denudation rates and increasing ocean salinity measurements, which gave immense age ranges (from 20My to 1.5Gy); however, the question was definitively settled by Lord Kelvin, who calculated, based on the assumption that solar heat was due to gravitational contraction, that the Sun (and therefore the Earth) was about 60My old. Since Kelvin was the world’s foremost physicist, that settled the question once and for all, which turned out to be about two years (when the Curies discovered radium). Kelvin never did accept radioactivity, feeling that the radium had absorbed heat from elsewhere and was now giving it off again.


Jackson concludes by covering the early days of radiometric dating up to 1956, when Clair Patterson published 4.550Gy for the age of meteorites (and therefore the solar system, and therefore the Earth).


Entertaining, and probably quite useful for debates with YECs, who always seem to dredge up sedimentary denudation and salinity arguments. It would have been nice to include just a little more explanation of why these methods didn’t work. But you can’t have everything. ( )