Re: Shrinking Earth



In article <FsYkf.11970$ea6.3999@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Chriso wrote:
> It is an expansion factor of 4,
>
In radius. One dimension. Cube it to get the volumetric expansion.

> but as you point out the hypothesis fails
> if you assume cosmic abundancy applies to the Earth's interior. Maybe it
> doesn't?
>
I'm assuming that the cosmic abundance applies to the Earth as a
whole, not just to the core. I don't for one second deny the existence of
differentiation within the body of the Earth, but that doesn't matter. It
doesn't hugely matter if the expansion takes place in the core, the mantle,
or anywhere much more than 50 km below the surface, because the expansion
would settle out in a geological eyeblink and you'd end up with a (slightly
larger) oblate spheroid.

> The core of Earth is still molten and Mars has a solid core so
> something is different.
>
Something is definitely different. It's something incredibly subtle
that astonishingly astronomers have barely noticed it. The fact is ... Mars
is smaller than Earth. And small things cool down faster than large things.
You can verify this at home if you like, with a 2 pint jug of hot coffee and
a 1 pint jug.
Working out the consequences of the smaller mass of Mars for it's
thermal history would be a useful exercise in "back of the envelope" work.

> There are other radioactive elements, and what
> about a fast breeder scenario where radioactive elements are being
> produced as a byproduct of the fission chain?
>
All the radioactive elements are vastly diluted by an unreactive (in
the nuclear sense) mass of iron, silicon, magnesium, and oxygen. By the way,
there's a *very* good reason for the commonest elements in the (degassed)
cosmic mix to be unreactive in a nuclear sense.
Fast breeders require massively larger concentrations of radioactive
nuclides, as well as being quite stringent in their requirements for
moderators to reduce the energy of the liberated neutrons.

> The chasms on Mars would fall into the category of natural phenomena that
> might be explained by an expanding Mars. They sure look like stretch
> marks to my untutored eye.
>
Don, to whom you seem to be paying some attention, has some bizarre
aversion to the idea of subduction - the sinking of oceanic crust plates
into the depths of the Earth, along more-or-less linear zones. Probe him a
little on this and you'll see a psychotic reaction that would, I hope, alert
you that this guy isn't necessarily talking from a position that he's
arrived at by reason.
Much to Don's disgust, the plate tectonic model of the surface of the
Earth has been arrived at through the patient collection and collation of
evidence from many fields. Don seems to prefer his moment of blinding
revelation.

> The physics of the Earths's core would have to be beyond our normal
> experience and understanding with P & T way beyond what we are familiar
> with
>
"Beyond our normal experience" does not mean that it's inaccessible
to calculation, or more recently, experimental study in tetrahedral diamond
anvil presses heated by lasers. Here's a link to one of the several groups
working in this arena http://www.gl.ciw.edu/multi-anvil/ .
Just because it doesn't happen on the sidewalks of Kinshasha doesn't
mean that it's totally outside our knowledge.

> and because of the differentiated nature of the Earth nearly all of
> the heavy elements available in the primordial sphere would have found
> their way to the core providing a reservior of long half life elements.
>
Actually, they're in large part "incompatible" elements - they get
concentrated into the silicate phases rather than the metallic or oxide
ones.

--
Aidan Karley FGS
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

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