Evening star., 1932-06-29
SCIENCE MEASURES
METEOR|TES' AGE
Development of Sensitive
~ Method Reported by
German Physicist.
BY THOMAS r. HENRY.

The age of meteorites now can be
measured.
Development of an extraordinarily
sensitive method for this hitherto i'm
possible measurement has just been re-
ported by Prof. F. Paneth, German
physicist, to the Committee on the
Measurement of Geological Time OF the
National Research Council.
Applying his method to samples OF
these celestial visitors, collected all over
the word, including several from the
United States, Prof. Paneth finds that
the Oldest cannot boast of more than
5000, 900 years, which is well within
the time since the formation OF the
solar system. This leads to the conjec-
ture that they are parts of the solar
system. ,.-
The method reported by Prof Paneth
has far-reaching applications to other
time measurement problems upon which
the American committee Is at work,
especially the determination of the age
of deposits of copper, silver and other
metals which are very family radio
actives It consists in determination OF
the amount of rare gas helium, product
of atomic di5integration, in a given
amount of the metal.
Supplants Lead Method.
Hitherto the most reliable method OF
measuring geological time has been by
the lead-ratio method. The two radio
active elements, uranium and thorium,
disintegrate at fixed rate into final
state which is form of lead differing
in atomic weight from ordinary lead.
The amount Of lead in proportion to
these parent clements in a sample Of
10 nf
Is one of the by-productS of the disin-
tegration. 1t is, however, light gas
which will not enter into chemical COM
bination with anything in nature, and
which, consequently, escapes easily and
becomes diffused in the atmosphere.
Lead, the heavy metal, stays put" In
the past measurements of the helium
content has given much lower figures
for the age of deposit than the lead
method. -
The advantage of the helium meas
determined in much smaller quantities.
The geologist using She lead-ratio
method can consider only the special
kind of lead which results from atomic
disintegration, and in small samples 1t
is impossible to distinguish this accu-
rately from ordinary lead, which has
not time significance.
Hitherto" says Prof. Paneth, the
lead method has been almost exclu-
sively recognized as reliable. There
are, however, materials which hold the
helium completely fast-the metals.
Even by heating an iron meteorite to
1000 degrees Tor many hours only a
neglgibly small fraction OF the hellum
Is dissipated, obviously only that close
to the Surface. We can therefore as
sumo with certainty that the amount:
of helhlnn which has been formed since
the consolidation of the peteorite still
is completHly iliclossS. Only the helium
from The ring may have escaped.
Accuracy Increased.
Here the heliufn is just as reliable |
as the lead method, over which it has
sone advantages, and we are in a posi- !
ton to test for helium in small guam |
titles. Iron meteoritess contain helium |
only in the order Of hundred thou
sandth to n1illionth Of a cubic cent? |
meter per6ranls BY a special method |
of disselRing the meteorite away from
air we can measure a rnillicnth Of a |
cubic centiineter of helium with max |
imum errcr OF per cent. BY using |
several grams Of meteorite 1t is always
possible TO increase the accuracy OF the
helium measurements in proportion.
1.-The 1000, ,000th to the 10000, ,000,-
000th part to gram of lead, formed
according to the laws Of radio-activity
by the same decomposition, cannot be
recognized in the presence of much
larger amount OF normal lead present
in the meteoriteg, for one contains on
the average an amount to which the
lead isotope formed by the decomposi-
ton of uranium and theorium would
not be even one part per thousand.
"It appears that to determine the age
Of iron meteorites the helium method
is the only way yet applicable, and the
customary objection of the possible es-
cape Of heliiirn does not apply. What
applies to iron meteorites also applies
to native metals. 1t is. probable that
the error from the escape Of henum
becomes important only In the radio
active minerals which contain much
helium, to which investigation hitherto
has been confined.
For the iron meteorites we have
estimates of age for which there is still
an uncertainty, because they give us
maximum values, but the particular In
terest is in the maximum age, because
before all It must be decided whether
the age of the nleteorite Is not too
great to consider it as belonging to our
planetary system. The highest age yet
ascertained seems to be not above
5000, 900 000 which is within the time
since the formation Of the solar
system"