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The theories and details of Plate Tectonics are extensive and involved. Numerous texts cover the current knowledge of the subject well. It is generally accepted that the plates normally "slide" around on top of the Mantle beneath. Hawaii represents excellent evidence of this. A single upwelling hot spot in the Mantle keeps breaking through the thin Crust in that area, continuously creating new islands as the Crust moves northwest above it. The Big Island of Hawaii is the newest and most volcanically active, and a new island (now just a seamount) will break the water's surface in a few thousand years to the southeast of it.
I suggest that many of the tectonic plates are generally larger in extent than the dimensions of the Mantle convection cells beneath. Therefore, each plate can experience frictional pulls in various directions by the various Mantle convection cells whose tops are moving in different directions in the Mantle beneath. Regarding the Pacific plate, the premise is that there are effectively more cell tops moving Northwest than in other directions. The plate's structural integrity keeps it intact. This maintenance of that plate's structural integrity is possible because the UNDER surface of that plate is relatively smooth, so friction due to the various underlying Mantle convective cells tend to slide rather than grip enough to tear it apart. The upwelling hotspot which is creating the Hawaiian Islands is evidence of a cell boundary which is not moving Northwest with the average of the rest.
When a continent, or a full mountain range is originally forming on the Earth's surface, the Crust becomes depressed there under the additional weight, (due to isostasy). (This also happens dynamically when a glacial ice sheet forms and over-rides a continent.)
In such situation, a new "obstruction" or "friction point" exists on the bottom side of the Crust. Such a new friction area can cause either or both of two different effects. First, the plate could now be ripped apart due to greater differential stresses (due to the better "gripping" between the moving Mantle convection cell and the Crust above it) acting on the plate. Second, if the plate has enough structural integrity to withstand the new stresses, the plate could suddenly start moving in a new direction, or possibly rotate around the new friction point.
Consider the situation where a substantial new mountain range develops (in Alaska, for instance.) Shortly, (within a hundred thousand years or so) the Crust sags there and now represents a frictional drag point between the Mantle and the Crust. The mass flow rate of Mantle material at the top of a Mantle convection cell represents FAR greater amounts of mass than the relatively thin and light (low density) Crust above it. Such a drag point would then have little effect on the motion of the Mantle. However, it would have enormous and immediate effects on the local Crust's motion. A new mountain chain near the edge of a tectonic plate could cause a new deep penetration of the Crust in that area into the Mantle in that area. Depending on the specific flow vectors of the Mantle materials in the area, that could cause that whole plate to (fairly quickly, in a few million years) pivot around conceivably turning a continent or sub-continent around geographically. Additionally, such a new, deep penetration could penetrate into, and interact with, a SPECIFIC Mantle convective cell flow, whose flow rate and direction could now dominate the forces on that tectonic plate and therefore to cause it to suddenly accelerate in some new direction.
The present movements of the continents is rather slow. Calculations of the amount of heat coming up through the Earth from original heat and from internal radioactivity, suggests substantial Mantle mass movement rates. These relatively high Mantle velocities in their convection cells would seldom be noticed in our surface world, because the many Mantle convective cells under a specific continent would move in random directions. The net effect of these many frictional drag effects would be a small net velocity vector that we actually measure as continental movement.
The present premise suggests that minor examples of such dynamic friction points happen regularly. Numerous current examples could explain the complexity of present plate motions. Very precise internal radar Mantle mapping will hopefully determine the current Mantle convection cell locations. Once that data has been obtained for the whole Earth, it will be possible to mathematically integrate all of the boundary frictional effects to calculate the total force acting on each tectonic plate. Then, the direction and speed that each plate SHOULD be moving will be available, which could then be compared to empirical measurements of movements already measured.
The present premise suggests that a major example of it may be what happened about 550 million years ago. "Major example" just means that the friction significantly redirected a large plate, such as the current Pacific plate. If that plate suddenly turned or started moving in a different direction, its motion would push many of the other plates around as well. Up until 550 million years ago, a limited variety of very successful living species had prospered for a long time. There had been little environmental stress to cause much evolutionary change in the existing species. Very slow, consistent, methodical plate movement would allow an equally slow and methodical evolution of adaptation of the species for success in the environmental conditions present. If each generation of a creature or plant only existed 20 feet farther North (due to tectonic plate movement) than its predecessor, very minimal evolutionary stress would exist, and virtually no evolutionary adjustment would be called for. Even plant life could adapt at such a rate.
If those organisms and plants were on a tectonic plate that was subjected to the sort of rotation or change of translational velocity described above, then they would be fairly quickly carried to a location of significantly different environmental conditions. This would necessitate rapid adaptation for some species to survive and prosper. And then, within a few million years, the Crust's underside pivot or drag point may have worn down and the initial plate movement would have continued. Reasonably constant climate situations would again ensue allowing the new and old stable species to prosper with little additional evolution.
The net effect of this sort of episode would be rather rapid change in environmental conditions, that would inspire rapid evolutionary changes in many or most animals and plants. Some would be able to adapt, and those species would survive and prosper. Other species would not be able to successfully adapt to the new conditions, and they would become extinct.
Recent findings have strongly established that much of the evolutionary changes in animals and plants has happened in brief "spurts" rather than as slow continuous change. This current premise offers an explanation of how there could be very long periods of Earth's history where there is little significant evolutionary change and where there are "boundary-events" where great changes in biological life forms occurred in short periods of time.
The present premise suggests that a major tectonic plate movement shift occurred about 65 million years ago. The sudden climate changes at that time would explain the dieout of dinosaurs and the significant evolutionary changes in many other lifeforms at that time. This explanation does NOT require a giant meteor or asteroid to impact the Earth to cause that extinction, and it seems much more physically likely. This is particularly true, because the K-T boundary event that is associated with the dinosaur extinction is not the only example of this phenomenon. Another, possibly even more major, episode occurred about 550 million years ago, and the fossil evidence clearly suggests that there have been a number of lesser incidents of non-continuous evolution and of massive extinctions throughout the fossil record.
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C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago