Evening star., 1954-12-10
Time Ronge Expanded
On Carbon Atom Clock
Better Tools Enoble lsotope
To 10y Bare 5000 Years
By Thomos R. Henry

" tuosH0S Ne HtSUty
The dial of the clock Of life soon
win be doubled In size-its time range
extended from $4,000 to $4,000 years.
This viii happen In the near future
with more precise tools for chemical
analysis and radiation detection, says
DR.. j. Laurence Kulp. director Of the
Lamont Geological Laboratory Of Co
lumbia University and one Of the coun.
try's foremost authorities on geo
chemistry.
The "clock" Is the radioactive isotope
Of carbon which Is constantly being
created by the cosmic ray lombard
ment Of nitrogen in the upper atmos.
phere. It combines with oxygen to form
carbon dioxide, adding to the very small
amount Of this gas in the atmosphere.
1t is extracted by plants to form part
OF their own structure through the
process of photosynthesis. the base Of
the entire pyramid of life. Animals
which eat the plants get some of the
radioactive carbon molecules In their
own bodies-in proportion to ordinary
carbon which has been quite precisely
determined.
Margin Of Error Small.
The radioactive carbon has q half
life Of about 5000 years. Calculating
from this basis the age of any organic
remains UP to about $4,000 years can
be determined with small margin Of
error by finding the amount OF the
radioactive element actually present.
compared to the normal amount for
living things. The method has been
used to date organic remains like wrap
pings of mummies from Egypt and
Peru. prehistoric bison remains from
Alaska. and human bones from ancient
caves of Europe.
But with techniques available up to
now $4,000 years has been about the
limit. After 5000 years only half the
original radiocarbon contents of q bone
or piece Of charcoal will be left In
10000 years this will be reduced to a
fourth. In 10000 years only q sixty
fourth Of the original amount is left.
With the development predicted by
DR.. Kulp, calculations can be made with
less than thousandth of the original
radiocarbon. This will carry the dating
considerably beyond the time when any
OF the present human species are known
to have been on earth.
The Importance of radiocarbon COW
erlng the range of human history. DR..
Kulp says, has obscured the importance
OF other atom clocks which, used as
checks on each other. carry the range
back almost to the creation of the
earth, or at least to the time the pres
ent crustal materials were formed.
Potentially most valuable is the
potassium clock" whose range extends
from the earth's creation about 5 bill
lion years ago, to 10 million years ago.
The common occurrence of potassium
in nature makes it ideal for dating the
planets older rocks. For the past TO-
600 millenniums. however, the amount
originally present has been reduced to
a hardly measurable trace. A similar
clock-a radioactive isotope of the rare
element rubidium which is naturally
transmitted into strontium-has a diff
ferent range-from billion to 100
million years ago.
Methods Improved.
AAlC IA ot VI IdulOdCIlFE
was the rate Of decay of uranium, an
extremely slow process. Methods Of
analysis. DR.. Kulp says, now have been
improved to the point where objects
1 billion years old can be dated with
an accuracy of about 98 per cent.
Excess ionium. radioactive isotops
of thorium. found in muds at the bot
tom Of the Atlantic Ocean, is being
used to study the sedimentation rate
there. Finally tritium, or triple-weight
hydrogen which is radioactive and is
the supposed basis of the hydrogen
bomb. is being used as an identification
tag for air masses. The moisture in
each air mass can be dated, thereby
enabling meteorologists to study move.
ment and mixing in the atmosphere.
With the delicate methods now avail
able, the Columbia scientists stress, the
four available atomic clocks can be
used to check on each other. Ali are
subject to errors-perhaps rather large
ones. but it hardly can be expected that
all four would be keeping bad time at
the same period.