Question

Plate tectonics is the theory that the Earth’s crust is made up of plates that glide over a layer of mantle. A prediction of this theory is that the plates will move relative to each other as they move over the mantle. To test this hypothesis, a scientist places a marker on two adjacent plates to measure their movement over a decade. What would be the expected result of the experiment? How would you interpret the results if the scientist sees no movement?

Answer 1

The plates should have moved, and if they have not then the plate tectonic theory is incorrect

Answer 2

The expected result of the experiment will be that the markers are either further away from each other, or closer to each other, thus confirming that the tectonic plates are in fact moving and are not static.

On the other hand, the distance between the markers can remain the same, and that is a tricky situation. This may indicate that there's actually no movement, thus making the theory nit valid, but it can also mean something else, that the scientist put the markers on two tectonic plates that are moving in the same direction with pretty much the same speed, so even though there is movement, it can not be noticed by the markers. A nice example will be if there's markers set on the North American plate, and on the South American plate, they move at pretty much the same speed, and also in the same direction, so with setting up markers we can not get to valid results.