Evening star., 1950-10-13
Aqe of North America
Put at z Billion Years
Oldest Port of Continent
Believed in Cunudiun Belt
By Thomos R. Henry

North America is at least two billion,
400 million years old.
It has reached its present size in eight
major jumps or ages of mountain build
ing.
The oldest part of the continent which
can be determined is belt running east
and west through Northern Quebec On
tario and Manitoba.
This was reported to the National
Academy of Sciences meeting in Sche-
nectady, N. Y, today by DR.. P. M. Hur-
ley of the Massachusetts Institute OF
Technology. The findings were based on
the rates Of radioactive decay Of three
exploding elements-uranium, radium
and rubidium.
Rough Measure OF Age.
Half of all the uranium originally
present in rocks will change into dis
tinguishable form of lead in about AZ
billion years. Thus the ratio of this lead
and the uranium present in rock sam
pie furnishes a rough measure Of the
age of the rock.
A peculiar form of the rare element
rubidium undergoes the same process in
about go billion years, decaying into
form of the rare element strontium. The
IdGlO VI LIIc LWO CIlcChS Ou bIlc
measurements.
The halos in rocks caused by the alpha
particle emissions of radium furnish
another check. In the case Of the ancient
Canadian rocks the three agree roughly.
There is considerable evidence, 1t was
reported to the academy. that land above
present sea level existed even before
these oldest rocks were thrust upward,
- 10 k~A .f = ~
been found.
The Canadian rocks are the oldest in
the world with the possible exception
of some in Karelia. an Arctic prov
ince of Russia. There is reason to
believe. from astronomical evidence, that
this planet itself cannot be much more
than billion years old. Thus North
America dates back to within about a
half billion years Of the beginning Of the
earth.
Island for Milleniums.
For many milleniums, it may be as
sumed, the Canadian area remained as a
small island. Then came another period
of few million years of mountain build
ing. At last there were eight mountain
islands with the spaces between them
gradually being filled in by the constant
processes of erosion. Quite recent ad-
ditions were the Appalachians and the
Rockies. Comparable data is not avail
able on the other seven continents.
The basic mechanism of mountain
building remains unknown to science.
A thesis widely held up to now is that
the earth is cooling and that its outer
crust is wrinkling like the skin of an
orange as it dries and grows old An
alternative proposal to the academy
members today was that it could be due
to heating earth, although by some
what more complicated process.
At considerable depth it is assumed,
the composition of the earth is essen
TALLY the same as that of stony meteorites
the shooting stars" which are believed
to be fragments of another planet about
the size of the earth which exploded.
Experiments at the Geophysical Labora-
tory Of the Carnegie Institution here in
Washington show that with a melting
earth this is about what would result,
with the heavier constituents sinking to
the bottom and the lighter rising to the
top. Then various alternative processes
of heating and cooling would produce the
internal forces essential for mountain
building.
The hypothesis advanced today was
that continent grows in spurts. The
present may be in Quiescent period OF a
few hundred million years when the out
lines of the continents and the seas are
relafjUalv stable