How does sonar help prove Wegener's theory of continental drift?
Sonor showed the mid Atlantic ridge dividing the plates like the north Atlantic from the European plate. This provides evidence for Wegener's theory of Continental Drift.
Wegener's theory was based on the outlines of the continents especially between South America and Africa. Sonor showed that these outlines extend under the oceans.
Wegener's theory was rejected because it violated the geological principles of gradualism and uniformitarianism. Gaylord Simpson argued against the theory of plate tectonics as late as the mid 1970's. The splitting of the plates did not correspond to the time line of biological evolution according to the then standard time line.
There is now solid empirical evidence in favor of Wegener's theory of Continental Drift ( now called plate tectonics ) Sonor is part of the empirical evidence that supported the theory.