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Re: Oklo



On Thu, 01 Jan 1998 20:24:11 -0400 (EDT) LUDWIK KOWALSKI said:
How old are oceans? How old is water?

The competing theory is that much of our water came from outer space (and is
still comming). There are a lot of comet like fragments floating around and
current evidence suggests that huge quantities of these fragments enter our
atmosphere every day. Recognition of this possible source does not alter the
conclusion that most of our water is old. It just shows that there is always
more to learn

I called a geologist friend and he said:

1) The oldest known sedimentary rocks were formed 3.7 billion years
ago. This indicates presence of water.
2) Most geologists think that water was introduced to the surface of
our planet through vulcanic activities which certainly were much
more intense in the distant past than today. It is reasonable to
assume that most of water we have (1.5*10^9 cubic kilometers) was
already above the crust 3.5 or 4 billion years ago. Solidication
of the crust accured about 4.5 billion years ago.
3) The oldest continental lands (Australia, Greenland, Northern Canada
and South Africa) were above the ocean level for at least 3*10^9 yrs.

A simple calculation shows that the abundance of U235 was as follows:

t= 1 billion 2 billion 3 billion 3.7 billion 4 billion 5 billion
1.6% 3.6% 7.8% 13% 16% 30%

Why is the isotopic abundance of U-235 so uniform on earth, except
for Oklo?

I do not know. If Oklo was a natural reactor 2 billion years ago then
there should be many Oklos, especially when the U235 concentration was
higher than 5%. Ask your local experts and share what you learn.

Ludwik Kowalski