Why were Alfred Wegener's ideas about continental drift discounted for so long?
Alfred Wegener (1880-1930) was a German climatologist and geophysicist. In his book The Origin of Continents and Oceans (1915) he proposed the existence of Pangaea (Greek for "All Earth"), the supercontinent that contained all of the land mass of Earth until it broke apart about 200 million years ago.
The reaction of the scientific community appears to have been uniformly hostile; one American scientist suggested that "If we are to believe [this] hypothesis, we must forget everything we have learned in the last 70 years and start all over again."
It wasn't until the 1950's that his ideas started to be accepted, after findings in paleomagnetism and oceanography begat the science of Plate Tectonics, which showed that the continents indeed move.
Although science may not have been convinced of his theory in 1915, and it required ironclad proof that didn't appear until after World War II, I wonder if the main reason his theory was not accepted at the time (1915) was that he was on the "wrong" side of World War I -- anything from a German scientist at that time must be suspect to the rest of the international scientific community. International politics may have caused his work to be sidelined.