Evening star., 1940-03-02
Of Stors, Men
And Atoms
Notebook Of Science Progress
In Field. Laboratory
And Study
By Thomas r. Henri.

Ano Stuoy
By Thomas r. Henrv.
Two geological watches, keeping per-
feet time since the earth was born, have
just been checked against each other and
agree in fixing the age Of the planet be-
tween 1,7O0, 100000 and 1900 900 900 years.
One is deposit Of mineral known
as monazite on the shore of Lake Win
nipeg in Manitoba. Hitherto valued as a
source Of rare earth minerals necessary
for gas masks, this monazite contains
tiny specks of uranium and thorium, the
heavy elements which change into lead
at measurable rate over periods of
millenniums. The amount of certain
forms Of lead in sample compared with
the amounts OF uranium and thorium fix
the age of the rock itself.
This mona1te has just been analyzed
independently by DR.. H., v. Ellsworth,
chemist of the Canadian Geological Sur
vey, and DR.. F. l.. Hecht of Vienna, ac-
cording to reports to the Geological Time
Committee Of the National Research
Council. The amounts Of the pure min
eral which can be obtained from the
Canadian deposit are extremely minute.
The Austrian chemist was furnished
sample because he is considered the only
man in the world at present equipped
for the very delicate chemical micro
analysis necessary.
Both the German and Canadian analy-
ses Of the same material, however, gave
age estimates very close together-in the
neighborhood of 10000 900 years-ac-
cording to DR.. John Putnam Marble,
vice chairman of the committee which is
serving as a world clearing house for
earth age measurements.
The second watch" is rock deposit in
the Karelian Peninsula, near the Arctic
Circle and just on the Russian side of
the border. 1t contains both CRYSTALS of
monazite and larger samples of nearly
pure uranium For the past two decades
these rocks have been recognized as
analyses, about Is years ago, gave a
round figure Of approximately 1000 OO0,-
600 years for the time they had been in
existence in their present form. In the
meantime many sources of error have
been found and the latest determine
tionS, just completed by the state radio
logical institute in Moscow, cut the age
by at least 1000 900 years. They check
the Canadian figures within a few mil
lion years, says DR.. Marble, and this is
as close as can be expected, considering
the difficulties of analysis.
The problem, he says. is becoming more
complex all the time. There are at least
two forms of radium and two or three
of thorium. Each breaks down into
different kind of lead alta different rate.
All these kinds of lead are different
from ordinary lead. which also occurs in
two or three forms, or isotopes. The
exact amounts of all varieties OF all three
minerals must be determined in almost
infinitesimally minute quantities.
Neither uranium nor thorium, DR..
Marble explains, could have existed as
fully formed elements below the surface
of the sun. The earth is generally be-
ieved by astronomers to have been torn
with a passing star. Hurled into the
cold of space it quickly solidified It's
surface was covered with barren, igneous
rocks, of about the same sort as are
formed when molten lava cools. Then,
for the first time, the radioactive min
erals became fixed In their present posi-
tions.
So any possible age determinations can
go back only to the earth's solidification.
But this probably occurred in only few
thousand years, like seconds in consid-
ering the long sweep of geological time.
Naturally any fragments of the original
rocks are hard to find after the crush
ing of the millenniums.
Neither the Manitoba or Karelia rocks,
says Dr. Marble, are quite "at the bot
TOM" Chemical studies of igneous rocks
formation have shown that monazite is
one of the last minerals to form from
molten lava. The GRANTEES come first.
Nobody has yet found any of the very
ancient GRANTEES.
At the best, DR.. Marble says, probably
If another hundred million years is al
lowed for the infancy of the planet its
age is fairly well determined by the
Canadian specimens The Russian ma
terial, while more abundant, is more
complex, leaving much more room for
error.
The Manitoba deposits, DR.. Marble says,
are almost at the southern edge of the
Canadian shield, surface rock which cov-
ers most of the Dominion east of the
Rockies and which, entirely devoid of
any fossils, far antedates any life on
earth. Curiously, however, this rock
grows younger as it extends northward
and specimens analyzed from the neigh
borhood of Great Bear Lake show an
age of only about billion years.