The theory of plate tectonics was, at first, rejected by most scientists. Now most geologists accept that tectonic plates exist and that these tectonic plates can and do move. What is responsible for the change in how scientists think about plate tectonics?

The validation of seafloor spreading in the 1950s and 60s

Explanation:

The theory of seafloor spreading was supported by numerous evidence including thermal probes that showed that heat flow over the mid-ocean ridges measured up to four times those measured in general bottom sediments, which are taken as due to the presence of molten Earth material close to the ridge crest

The ridge crest also show signs unusually seismic wave velocities that are considered to be due to microfracturing and thermal expansion from upwelling magma

the answer is symmetrical : )