AGE OF THE EARTH—HOLMES 
tion for determining the age of the 
oceans. Adopting the simple hypoth- 
esis that, on average, the annual 
amount of dissolved sodium removed 
by rivers from the land has remained 
constant throughout geological time, 
he found that about 80-90 million 
years would be required to furnish the 
total amount of sodium now present 
in the oceans. This estimate he 
shortly afterward increased to 100 
million years. A few years later Sollas 
concluded that the probable limits 
were 80-150 million years. In 1910 
Becker, thinking it likely that the 
annual increments had been progres- 
sively greater in the past, reduced the 
probable age to about 60 or 65 
million years. Indeed, Becker was 
sufficiently convinced of the validity of 
these ‘‘short’’ estimates to declare 
that ‘“‘radioactive minerals cannot 
have the great ages which have been 
attributed to them.” 
It is therefore of some importance to 
consider the present status of the 
sodium method. It appears from 
recent discussion of the relevant geo- 
chemical statistics (see especially Con- 
way, 1942 and 1943) that practically 
all the “‘chloridized”’ sodium in river 
water represents oceanic salt, either 
blown inland and washed down by 
rain, or derived from saline deposits 
or the pore spaces of sediments. 
Allowing for such “‘second-hand”’ salt, 
the present annual addition of new 
sodium is about 6 X 107 tons. Even 
this figure may be misleadingly high 
because, as Lane has pointed out, 
analyses are rarely made of the 
water from rivers when they are in 
Hood. «iz; €.,, .when ;the.;content. of 
dissolved material is at its minimum. 
The total accumulation of marine 
sodium in ocean water and sediments 
is estimated at about 15 X 10" tons, 
less the amount initially present, which 
may or may not be negligible. Thus, 
on the assumption of past uniformity, 
all we can conclude is that the appar- 
ent age of the oceans is something of 
the order of 250 million years. But 
past uniformity can by no means be 
assumed. Present rates of weathering 
817369—49—_18 
231 
and eorsion are far too abnormally 
high to be representative of the 
geological past. Mountain ranges and 
land areas in general are now much 
more elevated and extensive than has 
usually been the case. Rivers and 
groundwaters are therefore unusually 
active, and, moreover, many of them 
drain regions that are thickly strewn 
with easily weathered glacial deposits. 
Finally, human activities of all kinds— 
agricultural, engineering and chemi- 
cal—have still further speeded up the 
rates of weathering and erosion over 
widespread areas. 
Only a crude attempt can be made 
to assess the effects of these considera- 
tions on the “apparent? age of the 
oceans. Fig. 1 illustrates the observed 
fact that the continents are made up 
of belts of rocks that have suffered in- 
tense compression, folding and thick- 
ening. If we imagine, going back- 
wards in time, all the folds to be 
straightened out, then the crustal layer 
responsible for the continents becomes 
increasingly attenuated and extensive; 
so much so that in the early days or 
geological history this continental layer 
must have been spread so thinly that 
its surface would be below sea level 
and the only lands would be a few 
volcanic islands. Since then, the con- 
tinental lands exposed to erosion have 
on the whole, and despite wide fluctua- 
tions, progressively increased in height 
and area. According to this concep- 
tion, the quantitative effects of de- 
nudation must have gradually in- 
creased from almost zero at the begin- 
ning to the all-time maximum of the 
present epoch. Roughly we may 
reckon that the time-average rate was 
probably between one-half and one- 
third of the present rate in respect 
(separately) of area, height, and relief. 
That is, it was probably between (1)? 
and (44)? of the present rate. The age 
of the oceans may therefore be any- 
thing between 8 and 27 times the ap- 
parent age of 250 million years which 
may itself be a minimum. Obviously 
the hourglass of sodium accumulation 
is a hopelessly variable timekeeper. 
The most that can be said is that its 
