From: dietz@interaccess.com (Paul F. Dietz)
Newsgroups: sci.astro,sci.space.policy,sci.bio.paleontology,rec.arts.sf.science
Subject: Re: Could intelligent extraterrestrial life exist in our galaxy?
Date: Wed, 23 Apr 1997 01:25:36 GMT

On 21 Apr 1997 12:07:48 GMT, Tommy the Terrorist
<mayday@super.zippo.com> wrote:

>  Maybe the planetary science people can correct me,
>but I haven't heard of uranium turning up elsewhere so far, and it's such
>a ridiculously dense material - I mean, fusion should stop at IRON from
>what I've heard, so it represents the product of a supernova.  And then
>the stuff turns up just lying around on the Earth's surface, instead of
>being dumped all the way down to the center of the core?  Such an
>accessible deposit of dense metal can't be a common occurrence.


There's a common myth that "uranium ends up in the core, because it is
heavy."

No, what ends up in the core is a heavy *phase*, a mixture of metals
and other elements that like to dissolve in those metals.  Uranium
does not partition into this metallic phase. Rather, it prefers to be
in silicate melts (and the late-crystallizing fluids that make
pegmatites).  Moreover, it prefers to be in the kind of silicates that
end up in the crust, rather than in the silicates that make up the
mantle.  Pick up an average piece of granite and you'll have a rock
that has considerably more uranium than you'd expect from the average
concentration of the earth (or, of the solar system.)

	Paul