Originally posted by NoExpert
Exactly right. Whilst the temperature of the mantle is not hot enough to melt the rocks at about 700km or closer to the surface, beyond this point and
at 'normal' conditions it would certainly be sufficient to produce a melt. The fact that this is not the case is due to the enormous pressure and
lack of water. Water is thought to be essential for plate tectonics as it lessens the temperature required to produce a melt from the solid mantle and
in effect allows for the lubrication of plates. Without water the plates would literally grind to a halt.
"Water is thought to be essential for plate tectonics" .... who thinks that? Saline or normal?
I don't think the scientific evidence supports this assertion.
Water--in the form of pore fluid (bearing in mind that our concept of water breaks down at certain temperatures, concentrations of minerals, and
locations (such as between grains)--is somewhat necessary to lubricate rocks moving due to tectonic stresses. As far as plate tectonics goes, the
issues become far more complex. I know the MoHo Discontinuity exists, but as for its nature I genuinely don't know.
I DO know that temperature and pressure increase with depth, and any water stuck between the crust and the mantle (ie, any water that could possibly
be lubricating the plates) would be far, far beyond boiling and under so much pressure that any crack or weakness would allow it to explode.
There's evidence of such a thing. Felsic volcanoes, such as Mount Saint Hellenes, cause so much devastation for exactly that reason (well, to a large
degree)--water in the magma hits the cooler, less-pressurized air and it effervesces like a soda bottle after driving over a washboard road (trust me
on that one). We know that there ARE such weak areas in the crust: we call them "oceanic ridges" and "black smokers". Since they're not exploding
(and even the pressure of the ocean won't be enough to stabilize the water in the magma), we can conclude that there's not significant amounts of
water in the MoHo.
The other argument that is no doubt going to be brought up is seismic data.
Don't get me started on that.
Well, actually please do, might learn something interesting
I'm not a fan of that data being much more useful than proving how the surface and very top crust of the Earth vibrates and interacts, I think when
seismologists start wishful thinking about some of these waveforms from surface readings and theorizing what they may mean, it's basically a
curve fitting of observed data to try to prove what they want to be true, not what they can actually scientifically prove is true, thus
such data could have been ascribed nothing more than a seismologists hunch 40 years ago about what he guessed was going on inside the Earth, and
henceforth the same data is ascribed a causation that becomes widely accepted in the field, yet no independent methodologies can verify it.
Even if the bell curve is perfect, or statistical significance very high, if those surface seismic waves are being caused by, say, any unrelated
periodic event inside the earth, lets say ... between huge exploding chambers of liquid/gaseous metahne/solvents/oil reservoirs once a periodic
pressure is breached and and ignition mechanism is attained in the chamber, boom. There goes that seismologists fantasy. Or .... whatever the data was
used to explain before.
The Earth is about 8000km thick. We have gone about 10km deep industrially, and for scientific tests only about 6-7. thats 0.1% in, less than the skin
on an apple.
The pressure gradient on the immediate surface seems to obey Newton.
But 99.9% of the physics, even the internal gravitational properties of how mass works, in a charged rotating plasma state, are not known.
The assumed universality of many laws of physics we take for granted as being so unquestionably accurate above the surface of the Earth, and in the
rest of the solar system, may behave totally different.
If I say that particles 20km under the surface of the Earth exert a force greater or less than those at the center, you can not, scientifically,
disprove that. Likewise, I can't prove it either.
Just making the point that this theory is very far from being falsified or pseudoscience, by any means. Even if it's not the most likely theory in
town, and currently lacks an initiation mechanism, it's very much still alive and still kicking. Even if largely forgotten by the establishment.