This theory simply means that all rocks are aligned to the Earth's magnetic field, and this field changes every few thousand years. How this supports plate tectonics is slightly more complex however. Firstly, in order to change a rocks alignment, extreme heat and pressure must be applied, which is only naturally found in the mantle. Secondly, near mid-ocean ridges in the seafloor, rocks that have been tested on differ from rocks of different age groups in that their magnetic fields are opposites. Quite clearly, this shows that rocks of older age groups are subducted at boundaries, and make their way to mid-ocean ridges to be upwelled into the crust once more. Along the way, these rocks change their magnetic alignment to the Earth's current field, meaning that they were in fact reused, and then when cooled on the seafloor, push out the older rock with undergoes the same change. Obviously, a magnetic reversal has not occurred in our time because such a thing takes many years to occur, but it is proven that they have happened due to magnetic testing of seafloor rocks. Magnetic rock anomalies show how crust is pushed outwards and farther away from a constructive boundary to a destructive one.
Laser Measure.
Scientists have tried for several years to predict where and when earthquakes will strike next unsuccessfully, but the methods they have used have been applied to modern tectonic theory. One of the main methods derived from this science is laser measuring. It is a very simple method of providing stable evidence that plates move. An example of this technique being used is at the San Andreas fault line, on either sides of the line. It works by a laser emitter/receiver being placed on one side of a fault, whilst a laser reflection disk is on the other. A laser beam is sent from the emitter to the reflector disk, where it is sent back to the receiver assembly on the emitter itself. When a plate moves, the laser or the disk also move with them, knocking the assembly out of alignment and when the beam is sent back to the receiver, it measures how much they are out of alignment, and converts that into a centimeter amount per unit of time (year, day, etc.
