When was the theory of plate tectonics adopted?
Probably around the late 1960's.
Alfred Wagner was the first in 1912 to propose the idea that the continents were not fixed, but in fact moved around. This hypothesis was almost entirely dismissed by the scientific community of the day. It took the next 50 years for evidence to accumulate in favour of the theory and by about 1970, the idea of plate tectonics was pretty much in the textbooks.
But in science, there is rarely a process where scientist sit down and informally agree that something is now an accepted theory. As more and more evidence accumulates on any new idea it either gets shot down in flames as not true, or more and more scientists become convinced by the evidence and gradually come to accept a new idea. But there are always holdouts - people that stubbornly refuse to believe a new theory, even with overwhelming evidence. In some cases, these kinds of scientists often cling to their competing hypothesis that is increasingly on its way out!
When I was a geology student in the early 1970's I had a professor that taught plate tectonics, but told us he thought it was a bunch of crap!
One famous scientist quipped one day that....."science some times advances one funeral at a time"!