.. Plate Tectonics and this Round Rotating Earth
           (....What round rotating Earth?....)

Fig.1  Convection models supporting Plate Tectonics   Neither spin nor roundness are relevant to plate tectonics.

The fact that the Earth is round and rotating  is wholly irrelevant to Plate Tectonics, which vests its model in the pure physics of convection and uses the homespun porridge-pot analogy - or (to fool the more scientifically 'intelligent' ) the bunsen burner and glass beaker of the laboratory.  In fact in many ways roundness and spin are a barrier to understanding the mechanics of Plate Tectonics, a hindrance and an embarassment, which Plate Tectonics sidesteps by its slogan :- "More research is needed".  In a 'container' such as the Earth which is spherical and has no sides whereby cooling may return, and seismic tomography shows no roots to spreading ridges, how is the cell fed, and how (and where) does it return?

How can the fact that the Earth is round and spinning be irrelvant to its geology?  Just think about that for a moment, about what Plate Tectonics is actually saying there - that whereas the first-order elements of shape and spin are central to concepts of the Earth's formation (as planetary accretion from whirling space debris), Plate Tectonics says that for the span of time that the Earth has existed as a differentiated planet, roundness and spin have nothing to do with any geological thing despite the obvious lie to this by global architecture of transform faults, the means by which convection 'up' is "transformed" to convection 'down'.

How can this be?  Even on its own terms Plate Tectonics should acknowledge the importance of roundness and spin, ..yet it doesn't.  The Earth (it is said) was brought into existence in a cataclysm of impact and accretion of whirling planetisimals and space dust.  The heat from collision caused the mass to incandesce, become properly round, differentiate into a core mantle and a crust, and rotate (remain spinning and orbiting the sun).   Residual heat is said to contribute to drive convection, but how much 'residual heat' would be left over after the Earth differented to form a core mantle and a crust?   If we say, "enough to break up the outer shell of the Earth (the lithosphere) and move it around", then why would a crust/lithosphere have formed in the first place?

And so radioactive elements in the outer core are then said to drive convection in the mantle. But research says (quote):-

"...It is presently controversial whether the Earth's core contains radioactive material. While the standard picture calls for none, several recent  laboratory experiments suggest the possibility that a large amount of potassium could have formed alloys with iron when the Earth was created."  (unquote)

However the half-life of Potassium (1.25 x 10^9 years against an Earth of about 4.5 x 10^9 years) means that even if it did exist, all the heat dissipated in decay would have been used up long before now.   Also, if there had indeed been radioactive potassium in the outer core then we run up against the  'shell' conundrum, which precludes convection (in the outer core), meaning there should be no magnetic field.  And in any case, the radioactive elements that are supposed to drive convection are typically contained in minerals which are concentrated in the continental crust.

So?  What?

But moving on from this conundrum, Plate Tectonics now says that the physical movement of convection at the Earth's surface is driven, not by the hot interior of the Earth, but (since it's all about temperature difference) by "cold, subducting mantle slabs" that have their extents already plunged into the hot mantle interior of the Earth.   How this 'coldness' of suducting slabs within a hot Earth is supposed to drive a convecting skin when the entire ocean floor is colder still,  is riddled with faults (abyssal hills) and is therefore already in segments that could sink at the drop of a hat if density and coldness was a point, is not explained by Plate Tectonics - nor how subducting slabs falling (vertically) under the force of gravity to cause back-arc basin formation, 'rollback',  and slab-pull to form spreading-ridges, can simultaneously generate sideways frictional drag on the overlying lithosphere in the opposite direction to provide partial melting and hangingwall volcanism - the "Fiery Ring of the Pacific".

The appeal of Plate Tectonics is clearly that it is apparently all things to all people.  In order to explain how subducting slabs get their leading edges turned down into the mantle in the first place, Plate Tectonics says that the continental crust pushes it down, and as well  invokes  "ridge-push": the height of the spreading ridge, 'pushing' downslope, forcing the ocean floor along and down the subduction zone - if you can for a moment suspend belief to accept that the scale and symmetries of the elements involved could allow that.  But the slope of the ridge is (says Plate Tectonics) an equilibrium cooling surface which is actually dependent on subduc tion in the first place - not an unstable gravitationally collapsing one which isn't; the height of the ridge is anyway determined by the pull of the subducting slab,   So, .. what?  Is 'pull' 'push'? ...Is extension compression?  Moreover the ocean floor is not crumpled by any supposed 'push'. It is heavily fractured by the old extensional ridge faults of abyssal hills.
 

"...abyssal hills are nevertheless the most abundant geomorphic structures on earth. ..."  "The topographic features known as abyssal hills characterize >30% of the ocean floor, and yet their origin has been the source of vigorous debate for over 40 years. "
http://www.geol.ucsb.edu/faculty/macdonald/Nature/nature.html

"...All of the continents put together do not cover even half the area occupied by the abyssal hills, which dominate 60-70% of our planet's surface. We hear a lot about the endless steppes of Asia and the immensity of the Sahara, but who writes about the earth's dominant geomorphological feature? The abyssal hills are left out of the textbooks because so little is known about them. They are hidden under 3 kilometers of water. "
http://www.science-frontiers.com/sf097/sf097g09.htm

As far as Plate Tectonics is concerned, the concepts and principles governing Earth deformation begin and end with convection, a process that takes place in many different 'shape-environments', the most favoured analogy of which to promote the model is in the illustration above.  Though it is indeed internal to the Earth (an  'indigestion' of the Earth's 'circulatory' system in a sense), in its conceptual essence it exists as something quite apart from the facts of the Earth's roundness and rotation - despite having its origins within it.

In other words, Plate Tectonics severs the link between shape-and-spin, and convection.  To Plate Tectonics convection  may just as well be taking place in a flat-bottomed pan, or in a square or irregularly-shaped room for all the difference it makes.   Plate Tectonics is simply saying that the only relevant point about the Earth as far as its deformation is concerned is simply that it is hotter in the middle than the outside, and that there exists therefore a heat gradient that in conjunction with the material properties of the mantle allow the supposition that the mantle is ductile on the scale of geological time, and therefore obeys the laws of viscous flow.  And therefore that convection happens.   And forget all of those other conundrums, which are subjects for "more research".

 
 

Fig.1 Seismic velocities and mantle density (Pressure (p-) waves travel faster than shear (s-) waves; shear waves do not travel penetrate the core.  (Image courtesy of ...)

However convection takes place in fluids, the mantle is solid, and movement in a ductile solid is surely not the same thing as movement in a convecting fluid. Well, ..if I think about it I don't really know, ..because how does one test behaviour on the scale of geological time?  The mantle rings like a bell in response to Earthquakes. It is as solid as a proverbial rock!   And what's more, according to p-wave travel times it gets more 'solid' (and denser)  with depth.   The empirical support for the notion that it may behave in a ductile way derives from observations of squiggles of convoluted fold structures in the Earth's 'brittle' crust (and therefore are logically more likely with depth where it's hotter (and therefore presumably more ductile).  Never mind that many of these squiggly analogues actually occurred in 'rocks' that were not rocks at all at the time of formation but were semi-solid or unconsolidated sediments that were subsequently lithified, the concept that ductile deformation happens over geological time is central, and time is anyway not a function in the equations used to describe convective flow in the mantle.

Ductile behaviour observed in the crust is a function of stress as much as temperature, and the structures describing stress in the Earth's crust accord with the symmetry of roundness and spin, which is obscured on plate maps. and ignored by Plate Tectonicists (however see ).   A solid being ductile under stress, is not the same thing as a fluid showing flow motion when heated.

Plate Tectonics glosses over these simple objections in the need to match mantle construction at spreading riges with its destruction at subduction zones, an unwarranted pairing that derives solely from the reasoning that there is no known way that the Earth can get bigger.  Or to put it another way, "Because we don't know how it can happen, therefore it can't."  But the "subduction zone" is simply a fault along which there has been massive dilation to allow emplacement of the ocean floor.  In fact according to Plate Tectonics, two ocean floors, ...the Panthalassa, and the one of the Present.  And not just any fault, but the one between the lithosphere and the asthenosphere.  Empricically, the geological evidence is - plain and simple - It has happened : the Earth has got bigger.  'Getting bigger', ..is the modus operandum of the Earth as it orbits the Sun.  (Mars failed.)

How we know.