Evening star., 1936-05-05

Is Mother Earth a gray old matron
of two billion Summers or an infant
planet not much more than a hundred
million years old?
She has been in existence for at least
1900 100000 years, says the National Re-
search Councils Committee on the
Measurement of Geologic Time, COM
posed of some of the foremost American
geologists. They base their estimate
on the lead ratio in radioactive rocks.
This has been challenged in a COM
mJnication to the committee by D. j.
Whitney. California chemist. with argu-
mentS which the chairman. DR.. Alfred
C. Lane of Tufts College. says are force
full if not incontrovertible. Mr.. Whit
neys contention. in brief. is that every
other measure of the earth's age except
those of radioactive disintegration. give a
time span of not more than one-twen-
tieth as great. Hence, he holds, some-
thing must be wrong with the lead-ratio
and closely related helium- ratio time
scale.
One of the measures of geologic time
considered most valid before the present
methods were adopted was the amount
of salt in the ocean. This all has come
from the land-leached out of the
primeval rocks. The rate at which salt
is deposited in the sea is known and
hence a rough estimate can be made
of the time interval required to make
the oceans as salty as they are today.
Mr.. Whitney calculates it as, at the
utmost, 100000 years-not allowing
for any sodium originally in the water.
Still another argument is that from
the rate of deposition of sediments.
When calculations are based on the
assumption that sedimentation has pro-
gressed at an UNMARRIED pace throughout
most of geologic time, Mr.. Whitney says,
the age of the earth turns out in rea-
sonable agreement with the estimate
arrived at by the lead-ratio method.
But this assumption, he insists, is en-
tirely false. Otherwise, he asks, how
would fossils of such creatures as
dinosaurs have been preserved.
Clearly" he says, sediments con-
tanning fossils of great terrestrial ami
mails must often have been laid down
very rapidly, and not at some such rate
as a foot per thousand years. If one
large fossil had to be buried rapidly to
prevent decay, doubtless a whole bed
would be formed in the same quick de-
posit."
He repeats the argument often used
against the radioactive measure of time
that uranium, thorium and their end
products, lead and helium, were in the
rocks when they came into place and
hence that their relative amounts give
no valid basis for an estimate.
N Il n
Another time measure, Mr.. Whitney
points out, is the amount of the rare
gas helirm-the second lightest Of all
the elements-in the atmosphere. 1t is
the first product of radioactive disinte-
grafton. Presumably it has been seep-
ing out of the rocks, as these have been
broken up. ever since the world began.
All the helium in the air, he says, can
be accounted for on the assumption that
this process has been in operation for
only about 10000, 900 years.
But even this is far too great an estl-
mate, he insists. In some places helium
is coming from the interior OF the earth
in far greater amounts than are re-
leased by the breakup of rocks. Thus
at one spot near Calgary 1000 cubic
meters day are issuing from the earth.
Near Petrolia, Tex. nearly four times
this amount is being exuded.
Meteoric dust. he satS. gives similar