Re: What is this convection cell nonsense


Darwin123 wrote:
On Aug 11, 12:24 pm, oriel36 <geraldkelle...@xxxxxxxxx> wrote:
On Aug 10, 6:29 pm, Darwin123 <drosen0...@xxxxxxxxx> wrote:

Be my guest,stick with your silly convection cells for crustal motion
but do not forget that it is useless for explaining why the shape of
the planet is not a perfect sphere.
The earth is oblate because it acts as a fluid. The convection
cells are not necessary to explain the oblateness, but they are
themselves a consequence of the fluid-like behavior of rock on large
scales of distance and time.
For convenience, I will use the reference frame of a rotating
earth. One can compensate for the noninertial aspect of the frame by
introducing a centrifugal force. I can explain it just as accurately
in an inertial frame, but I think this gets to the point faster.
There are three forces acting on a fluid element on the surface
of the earth. Two of those forces are gravity and elasticity. At the
poles, these are the only two forces. The balance bulls the surface
close to the earth. At the equation, due to the rotation of the earth
seen in an inertial frame, there is centrifugal force. The centrifugal
force pushes the earth outward, so it bulges at the equator. The three
forces balance out.
The elasticity turns out to be a fluid pressure, with few shear
forces. This is easily seen from merely a fluid statics analysis.
Because the surface of the earth approximately forms a geodesic with
respect to the sum of gravitational and centrifugal forces. The
effective gravitational acceleration of the earth is the same at the
poles as at the equator. Here, effective includes both gravitational
and centrifugal force. It wouldn't do that unless the rock really was
acting as a fluid on a long time scale.

Yes, ..so far so good. The Earth behaves as a fluid. (Oblate shape >
Spherical shape. etc..)


The small deviations caused by temperature differences couldn't
change the geodesic part of the problem.

Yes, .. But who says that temperature differences are the only way
you can get disturbance? The rocks are inherently different in their
viscosities, which must have a feed-through to differential behaviour
during spin, as the strresses built up in the spinning body are
released.


Hence convection is
irrelevant to the average shape of the earth itself. Treating the
earth as an axially symmetric body is no problem. This is merely a
consequence of the fact that the fluid in the earth is nearly static.
Once you allow a small amount of fluid motion into your model,
you open up the possibility of nonaxial geometry.

"Once you allow a small amount of fluid motion" ... = ductility
contrast (e.g. between the crust and the mantle (lithosphere/
asthenosphere).. But there is no necessity for that fluid motion to
be thermally driven. You are making precisely the point that needs to
be made. But that "fluid motion", we are saying, exists just by
virtue of ductility contrasts, and is structurally induced due to the
stresses in a spinning body, not to convection cells within the Earth


Differential
rotation the way you describe it is a fluid motion that is forced to
have axial symmetry. There is no law in fluid mechanics that requires
the motion of a fluid to have an axial symmetry.

Well, .. the weather has axial symmetry, the way it spirals towards
the poles on both sides of the equator.

It is this axial
symmetry that YOU propose that is ad hoc, not the concept convective
currents. Once you have a temperature gradient in a fluid under the
action of gravity, convective currents must form.

Maybe, ..but that's not what we see in the crustal structure that is
important. What we see as important is the huge dislocation that
exists between the crust and the mantle, and the subordinate
accomapnying structures (transform faults). And we're saying that, in
just having these shells across which we know there has been
detachment, is enough to give the rotational instabilities that will
give us the rotaional structure of the Earth that we see. (is staring
us in the face). And that's what the structural architecture of the
Earth shows: spin symmetry, ..in far more than just the transform
faults on the Atlantic floor Oriel is talking about. It describes the
entirety of global structure (and is ignored by Plate Tectonics).
Plate Tectonics tries to describe things in terms of arms and legs,
and denies the existence of the full human being.

Thus, it is really your model that seems to have the ad hoc axial
symmetry. Projecting the fallacy of axial symmetry on the plate
tectonics model is deceptive. No geologist or physicist ever said that
plate tectonic theory is inherently axial, let alone spherical. You
have been attacking a straw man model.

No, ..that's right.. Plate Tectonics' convection model could be
happening in a stationary body of any shape. It needs neither the
fact that the Earth is round, nor that it is spinning, to support it.
Whereas everything about the evolving structure of the Earth through
time describes the architecture of spin.

It's a crazy situation that PlateTectonics recognises the first-order
deviation from the spherical as being spin induced but not the smaller-
scale structures that describe that changing oblateness with time.
(That first order oblateness does not even figure in its entire
litany). That's the extent to which it is hung on convection cells.
It must have convection cells to maintain its false foundation, which
is the **assumption** that the Earth cannot be getting bigger, and
therefore that the mantle must be being returned at the same rate as
it is being created. It cannot even see the nonsense in that, which
is that if the oceans floors were being destroyed at the same rate as
they are being created, then they would never come into being in the
first place.

It might be difficult for people outside of this argument to
comprehend how such a simple point can be put on the side (and this is
for their benefit), but it is the crux of the issue. In order to make
Plate Tectonics work it must be assumed there was a previously
existing ocean floor (i.e., exposed mantle) to make way for the one
being created at the present day - one that they call "Panthalassa",
the last vestige of which just happens to have conveniently
disappeared today, just when we turn to look for it. And of course
the same constraint applies to it: it could never form, if it were
destroyed at the same rate as it is created.

Panthalassa is no more than a figment of imagination, but it is what
Plate Tectonics is built on - that and the assumption that the Earth
cannot be getting bigger (because we know of no way it can)

Nice to know physics has a future, and not all is answerable in the
current state of affairs there.

.

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