Evening star., 1936-03-10
STARS, MEN AND ATOMS
Notebook of Science Progress in Field,
Laboratory and Study.
BY THOMAS r. HENRY,

The latest computations of the earth's
age--or the age of various rock deposits
laid down at different stages of geolog-
ical history-have just been reported by
the Committee on the Measurement of
Geologic Time of the National Research
Council.
The Oldest rocks dated during the year,
according to this report, are some ura-
mum ores from the Province of Carelia,
Russia, which show the enormous time
span of 1880 100000 years. This is ap-
preached closely by some rocks from
Manitoba. whose age is calculated at
approximately 100000, 900 years.
The report, presented by the chairman
Of the committee, Dr. Alfred c. Lane Of
Tufts College, details the work being
carried on all over the world in deter
mining these great time intervals. Most
of the investigators have worked with
the lead ratio method. Radioactive
minerals, of which the chief is uranium,
break down into lead-a kind of lead
chemically distinguishable from ordinary
lead-at fixed rate. Thus the ratio OF
the lead to the original material conSti-
tutes measure of the time the breaking
down process has been under way.
The lead ratio method enables the
committee to date approximately events
in the earth's history contemporaneous
with the formation of the rock strata.
It does not constitute a measure Of the
actual age of the world itself, since the
material may have been present in gas
or liquid form long before it hardened
into rock. Hundreds of measurements,
nytr rhpYninpl
and physical methods, have been made
and are being correlated.
There may be a possibility, DR.. Lane
points out, of checking the lead-forma-
tion time scale by evidences of cyclic
phenomena extending over thousands Of
years.
Such, for example, is the cycle of the
plane of the ecliptic. The axes OF the
earth wander in relation to this plane so
that approximately every $4,000 years the
hemisphere which is nearest the sun
when the days are longest is reversed.
The Northern Hemisphere at present hap
pens to be nearest the sun in Winter and
farthest away in Summer. If this we're
reversed Summers would be very much
hotter. This would be attended by bio
logical changes which would leave traces
or evidence in the form Of rock building.
It is well known that there have been
such Summers of the ages--long periods
when Greenland had a temperate cl-
mate and equally long periods when
Antarctica probably was habitable and
covered with vegetation from which coal
veins were formed. The difficulty has
been that these biological meteorological
cycles do not SEEM to have produced
strata which could be used as calendar.
But recently, DR.. Lane reports, there
have been found in the Carboniferous age
levels of Kansas, dating from about 30O,-
900 600 years ago, repeated rhythmic sue
cessions Of strata with limestone GEN.
ters-with an average thickness of about
Is feet. About 1000 years, it is assumed,
are required to lay down a foot OF sedi-
ments. While 25,000-year cycles appear
somewhat too long to have been caused
by the reverSals of the hen1ispheres in
respect to distance from the sun. this
may have been the primary cause.
There has also been suggested, re-
ported DR.. Lane, rhythm of times OF
mountain building and of quiescence
with peneplantation. (The wearing down
of mountain creSts approximately to sea
level) Thus it is estimated that there
was period OF 21s, ,0oo, 900 years from the
great uplift attending the invasion Of
some Of the Oldest GRANTEES to the fiat,
low-lying continent which existed
throughout much Of the paleozoic period.