Evening star., 1952-12-12
Check on Eorth's Age
Adds ! Billion Years
Outside Limit Conceded
Now as About 5.4 Billion
By Thomos R. Henry

Now as About 5.4 Billion
BY Thomos R. Henry
The age Of the planet earth is being
pushed upward by a billion years or
more.
This is due to newly developed
check on her yearS-the rate. Of trans
mutation of the soft, Silvery, red-burning
metal rubidium into the closely related
metal, strontium.
The planet has been chary as woman
about revealing the secret of her age
and apparently tells different stories,
depending on how she is questioned.
Up to now, age estimates have been
based chiefly on the rate of transforma-
tion Of the highly radioactive element
uranium into lead. In approximately q
billion years half the atoms of the
uranium originally in the crust of the
earth exploded and eventually became
a special form of lead. In the next bill
lion years half the remainder under
went the same transformation. What
ever amount Of uranium lead found in
a rock was once uranium. The ratio of
the lead found now to the uranium
found now shows the length of time
the transmutation had been in progress.
Earlier Calculations.
Early calculations by this method
about so years ago indicated that the
Oldest crustal rocks were about two bill
lion years old-that is, about four times
older than the rocks showing the earliest
signs of life. Step by step, this age esti-
mate has been pushed up about another
billion years as older pre-Cambrian or
"pre-life" rocks were found. The Oldest
are in the so-called pre-Cambrian
Shield which covers most Of Northern
Canada and in the Kola Peninsula of
Northern Russia.
Astronomers were willing to admit
the three -billion-year estimate because
it checked with the present distribution
Of stars and galaxies which would be
about the same as observed at present.
if it had started that long ago.
Uranium and the closely related ele-
ment thorium long remained the only
radioactive substances known in the
earth's surface. A few years ago came
the discovery of the extremely rare
radioactive form of rubidium. Half Of
1t is transmitted into strontium in so
billion years. It offered a means Of
checking on the story told by uranium.
Consistently the rubidium- -strontium
ratio has indicated an age about third
greater than Is indicated from the ura-
nium-lead ratio of rocks in the same
formation.
Instead of billion years, according
to the annual report of the Geophysical
Laboratory OF the Carnegie Institution
OF Washington, science now Is willing
TO concede as an outside upper limit 81
billion years.
Still Another Check.
Still another independent check Is af-
1orded by two radioactive forms Of
the common element potassium. One
changes into calcium of a peculiar form.
Cne otner into the rare gas, argon, which
constitutes minute part Of the earth's
atmosphere. The half life of these
radioactive potassiums is about 400
million years. They tell about the same
story as does uranium, but less conclu-
Sively.
:, Carnegie scientists now are engaged,
IKE prosecuting attorneys, in checking
tnese stories against each other. One
ulnculty in the past has been in OBJ
tanning samples OF uranium, potassium
and rubidium from the same rock for
nations.
Last summer DR.. Gordon L. Davis NJ
ene Geophyslcal Laboratory staff and
MS associates were able to accomultsh,
this from three areas known tn he nre-
Cambrian--in New Mexico, Arizona and
California. The rubidium is contained
IN lepldolite, a lightly sapphire-colored
form OF mica, and the uranium and nm
tasSlum from rocks Immediately sur.
rounding it, Meanwhile, an extremely
precise method has been worked ont
py GeophySical Laboratory scientists
10 measure minute amounts of rubidum
ana the strontiun derived from II.
50-milligram sample is sufficient for a
full analysis-that is about a 500th of an
ounce-but DR.. Davis prefers to uorr
with samples twice as large.
The Geophysical Laboratory worker.
at present are concentrating on rubid-
lum. The pre-Cambrian rocks in the
United States from which their samples
were obtained are not very old. as such
rocks go. They average about a billion
years. Two samples, one from the
Winnipeg River area in Manitoba and
one from Southern Rhodesia. indicate
eli age, if the rubidium story is right. of
about 80 billion years.
rocks in the world. The Winnipeg area
Is at the southern edge of the great
Canadian Shield. Greater ages have
been indicated by the uranium ratios
farther north.
Age of CrustaI Rocks.
Any age found. of course, is only that
OF the crustal rocks from which the
radioactive elements are extracted.
They have been there since the mate
rails forming this crust came together.
How long this may have been after the
actual date of creation" cannot be de-
termined. Various lines of evidence.
however, lead to the assumption that it
was not very long-perhaps a few mil
lion years. at the most. Odd millions
dort mean much in calculating the age
OF the earth.
Life, so far as can be determined. first
appeared not much more than a half
billion years ago. The first fossils come
from rocks determined by the RADIO
actlve calendar to be about that old.
Still the actual beginnings Of life must
GO much further back. Animals ad-
vanced enough to leave fossil traces were
relatively high forms. Among the objec-
tives Of the present investigation is to
determine chemical traces due to life
processes far back in the sterile pre-