Re: Age of Earth, 1952 opinion
- From: "Frank J" <fnci@xxxxxxxxxxx>
- Date: 7 Jul 2006 15:25:21 -0700
Desertphile wrote:
From "Evolution of California Landscape," bulletin #158, CaliforniaDivision of Mines.
[...]
The Earth's Age
Although the age of the earth has been a much-debated topic for
centuries, recent improvements in scientific tools have allowed a more
accurate estimate to be made now than ever before. With the advent of
our knowledge of radioactivity, a new means for determining the age of
some earth materials was evolved, and the findings enormously expanded
the known length of earth history. Radium is an element developed by
the natural breakup of atoms of parent elements like uranium, thorium,
and actinium, which are contained in a few min-erals of the earth.
During the disintegration of the atoms, the valuable gas helium also is
generated. Radium itself decomposes into other elements, so that we
have a radioactive series. The final product of this natural change
seems to be one of the isotopes of lead. Isotopes are varieties of
elements having the same atomic numbers, virtually the same chemical
properties, but differing slightly in atomic weights. The lead-isotope
formed from decay of parent radioactive elements apparently does not
break up, and the rate of decomposition has been accurately measured in
terms of the half period of decay. Therefore if an uranium- or
thorium-bearing mineral is present in a rock, the ratio of the uranium
and thorium content and the helium and lead isotope content can be
determined. Only minerals from fresh or relatively fresh volcanic rocks
can be used, for in these alone the significant mineral grains have
been altered or disturbed to the least extent and material of mixed
source is not present. Certain corrections have to be made to allow for
changes which have occurred since the mineral was formed so that the
calculations are complicated. Helium seems less satisfactory for the
determinations than lead, probably because it can escape more easily
from rocks than the solid element. The oldest known minerals come from
Russia and Manitoba, Canada; their ages are 1,850 and 2,300 million
years respectively. Because volcanic rocks have been erupted at various
places over the earth or emplaced below its surface during the entire
known history, an approximate time scale has been set up. This
undoubtedly will be made more accurate and fuller as techniques are
improved and more determinations of mineral age are made.
There are serious discrepancies between determinations based on helium
and those based on radio-lead, but, in spite of this, all measure-ments
so far made indicate that the recorded history of the earth probably
exceeds a billion and a half years. Back of this known record there is
a long interval, perhaps a half billion or more years, from the earth's
origin to the formation of the oldest known rocks. The age of the earth
thus is between two and three billion years.
[....]
Don't be silly. How can there be a 1952 estimate of the age of the
earth, when it began in 1955, early '56 the latest? That's as far back
as I can vouch for. Many of those who rave about ID (which claims to be
science and not "creationism"), actually use the "were you there?"
argument. And since IDers never refute them directly, they must be
right. :-)
.
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