The main weakness was that Wegener could not explain how the continents could plow through the seafloor, another problem he had was that he couldn't find the mechanism that caused the continents to move across the surface. So scientists rejected his hypothesis.
The theory of plate tectonics took evidence from the seafloor that allowed the plates to move across the earth's surface. Scientists noticed a long chain of volcanic mountains in the middle of the Atlantic ocean and alternating parallel bands of rock with magnetic crystals of differing polarity. Scientists were able to deduce that new oceanic crust was being produced at the mid-ocean ridges (those volcanic mountain ranges in the middle of oceans) and that magnetite crystals in those rocks produced there were aligning themselves to the earth's magnetic field at the time. And because of this they were able to deduce that the new rock was pushing the older rock away from the mid-ocean ridge, in turn moving the continents beyond the older seafloor
There is a mantle plume in the middle of the Pacific Ocean where magma from deep within the earth's surface reaches the earth's surface. This forms a volcano there. As the Pacific plate moves across the mantle plume, new volcanoes form as old ones die because it is away from the heat source. These volcanoes erode away, and as they do so the islands formed by them slowly shrink until they are completely beneath the waves .
