Evening star., 1934-11-05
MYSTERY Of LEAD
BEING EXPLORED
Carnegie Experts Here Con-
slider Subject Vital in Fix
ing Earth's Age.
BY THOMAS r. HENRY.

The riddle of Is kinds of lead is
being untangled at the geographical
laboratory of the Carnegie Institution
OF Washington.
The fact that lead exists in two
forms - ordinary lead and radio
genetic lead-has long been known
and has been of fundamental i'm
portance in efforts to estimate the
age of the earth. The two leads diff
fer in atomic weight although they
have precisely the same chemical
properties.
The heavier. it is known, is the
end result of the decay of uranium,
heaviest Of all the elements, through
millions of years of radio-activity.
BY determining the amount of this
kind Of lead in deposit of uranium
bearing rocks a fairly accurate de-
termination can be made of the age
of those rocks. The origin of the
ordinary lead. by far the most
abundant, has been a mystery.
Confusion Is Reduced.
In cooperative work between DR..
Charles Snowden Piggot of the geo.
graphical laboratory and DR.. Fred
Allison of the University Of Alabama,
using the extraordinary sensitive
magneto-optical method Of analysis
developed by the latter, according to
the report issued by the National Re-
search Councils Committee on Geo.
logic Time, it has been found that
there are actually l6 isotopes Of lead
and of uranium. DR.. Piggot has
succeeded, according to his report,
in reducing this confusion to some
order through study of their COM
binationS and relative abundance.
The two kinds Of lead hitherto
recognized. he finds, are two different
combinations OF iSOtOpeS in order of
abundance, with the strong indica-
ton that ordinary lead Is itself
substance born out of uranium and
may still be very family radioactive
But the disintegration that produced
1t took place in the sun before the
earth was born
Whether or not these two kinds of
lead will ultimately attain to the same
lSotoplc condition, he says. only geo.
logical time can tell and that will
probably take several billion years
The fact that every lead we have
examined, both ordinary and radio
derived, is composed of the same num-
Der OF isotopes, of apparently similar
masses is Of the utmost significance,
for it is strong evidence that all the
substance We call lead derives ulti-
mately from the same origin"
Existed as Part Of Sun.
"If ordinary lead came into being
by whatever process all other ordinary
atoms did. and if this process is entire
ly distinct from and independent of
radioactive processes as we know
them, then it is extraordinary that
exactly the same number of nuclear
confgurationS should be produced by
two entirely different and independent
processes
The evidence indicates, DR.. Piggot
holds, that uranium, either in its pres
ent form or as some earlier progenitor,
existed in the materials of the sun
before the earth was created from it
and that a considerable part of this
uranium had already disintegrated
into lead. This lead. together with a
certain amount of the uranium then
existing, became part of the new
planet and both have led independent
existenceS ever since.
If We accept this hypothesis he
says, I'VE are forced to the view that
either sufficient quantity of radio
active lead-producing material re-
manned with the otherwise inert ordi-
nary lead throughout all the geological
and chemical changes and is now sup
plying these isotopes of radio-derived
lead which We flnd-Which is extreme
ly unlikely-or else that the ordinary
lead is now proceeding toward some
ultimate condition of radioactive in
ertneSS toward which the radio-derived
lead also is heading.
AT any rate these lower isotopes
appear to exist If it be true that
ordinary and radio-derived leads are
both running the same isotopic rate,
but that the former has a billion
years start on the latter one would
expect a greater accumulation of the
lighter iSotopes in the older, ordinary
lead than in the younger. This condi-
ton is shown to some extent. but not
so pronounced as one might expect"