Geoscience Reference
In-Depth Information
One of the authors whom Merrill cited was John Joly, a professor of geology and
mineralogy at the University of Dublin. Joly was one of the most prolific, invent-
ive, and diversely curious scientists of his era, writing 269 scientific articles and
several topics. 16 His interests ranged over the age of the oceans and the Earth, pa-
leontology, rainfall gauges, the diet of sea birds, tectonics, continental drift, the use
of radium to treat cancer, and the canals of Mars. Like Kelvin, Joly owned a yacht
and loved to sail.
In 1715, the English astronomer Edmund Halley, friend of Newton, had pro-
posedanhourglassmethodtotheRoyalSociety.Iftheamountofsaltinlandlocked
lakes like the Caspian Sea were measured at that time and “after some centuries,”
he said, then “we may by the rule of proportion, make an estimate of the whole
time wherein the water would acquire its present degree of saltness.” In other
words, the amount of salt in the oceans could provide another kind of hourglass.
Halley accepted that “mankind has dwelt about 6,000 years,” but Scripture
nowhere revealed “how long the Earth had existed before this last Creation.”
Halley wished that the ancient Greek and Latin scholars had thought to measure
and record the amount of salt in the sea, but since they had not, he recommended
that the Royal Society begin to keep track of the “present degree of saltness in
the Ocean . . . that they may stand upon the record for the benefit of future ages.”
The great Halley recognized a problem that we will come back to: the ocean might
have contained original salt, which would “contract the age of the world.” In other
words, if the oceans had contained salt at their birth, as though sand was already
present in the bottom of the hourglass, the salt clock would give an age that was
too old, but still that age would be the maximum possible. Thus the method would
“refute the ancient notion of the eternity of all things; though perhaps by it the
world may be found much older than many have hitherto imagined.” 17
By Joly's day, scientists had accumulated enough information to allow them to
perform Halley's calculation. In 1899 Joly, unaware of either Halley's suggestion
or of T. Mellard Reade's similar work, did the arithmetic, using sodium instead of
sodium chloride to “avoid the obscure question of its ionisation.” 18 Joly's calcula-
tion had the simplicity of the hourglass: divide the total amount of sodium in the
ocean, estimated at 1.5627 × 10 16 tons, by the rate at which rivers deliver sodi-
um to the ocean, estimated at 1.527 × 10 8 tons per year, and derive the age of the
ocean: 99 million years.
AccordingtoPatrickWyseJackson,thepaper“firedtheimagination ofbothsci-
entific and general audiences, and for perhaps a decade this 'sodium method' held
sway amongst geochronologists.” 19 The salt clock would turn out to be the last
grain of sand through the hourglass of the geological calculators.
Search WWH ::




Custom Search