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The hypotheses of large-scale continental movements, seafloor spreading and subduction, and the relative youth of the oceanic crust are contradicted by a substantial volume of data.Evidence for significant amounts of submerged continental crust in the present-day oceans provides another major challenge to plate tectonics.
The theory of subduction has other problems as well.The hypothesizes directional movements of the plates themselves are also being questioned using "space-geodetic techniques" such as "very long baseline interferometry (VLBI), satellite laser-ranging (SLR), and the global positioning system (GPS).Some scientists claim that these instruments have unequivocally supported the theory of plate tectonics.However, seismic tomography has actually provided strong evidence against the existence of convection currents that are large enough and strong enough to move continental plates.In fact, many geologists now think that the small upper layer mant Currently, the favored mechanisms used to explain plate movements are the "ridge-push" and the "slab-pull" methods.The existence of deep continental roots and the absence of a continuous, global asthenosphere to "lubricate" plate motions, have rendered the classical model of plate movements untenable.
There is no consensus on the thickness of the "plates" and no certainty as to the forces responsible for their supposed movement.
For example, the mid-ocean ridges, where new crust is thought to be produced, total 80,000 km in collective length.
However, only about 40,000 km of ocean trenches and "collision zones" exist.
Plate tectonics -- the reigning paradigm in the earth sciences -- faces some very severe and apparently fatal problems.
Far from being a simple, elegant, all-embracing global theory, it is confronted with a multitude of observational anomalies, and has had to be patched up with a complex variety of ad-hoc modifications and auxiliary hypotheses.
It seems like crust is being produced in more areas than it is being subducted. Certain specific examples are also interesting, such as the African plate.