Put simply, continents do not rise and fall into the oceans; they are composed of tectonic plates, moving across the earth very slowly and in different directions. As they move and run into each other, they cause earthquakes and the formation of mountain ranges. One plate may push underneath another, slowly to be absorbed back into the mantle (as is happening, famously, in Los Angeles), or adjacent plates may be travelling in opposite directions, causing earthquakes. In either of these scenarios, the continent itself does not disappear beneath the ocean; either the collision produces new mountain ranges (The Himalayas, for instance) or one plate is slowly drawn under the other. Plato’s – and Hancock’s – idea of a rapid sinking is not part of plate tectonics.
Although it is possible that a small land mass once existed in the Atlantic Ocean around the Azores at a time of much lower sea level, this does not correspond in size to Plato’s dimensions of Atlantis. We cannot have it both ways: if Plato was right about the existence of Atlantis, he remains our sole source of information about it, so if we want to find Atlantis, it absolutely must match his description in every detail, otherwise it is not Atlantis. Locating it in the Andes, the North Sea, on Santorini or anywhere other than in the Atlantic Ocean renders it something other than Atlantis and is not a solution.
Churchward’s claim that Mu was an island continent in the Pacific is more easily discounted. The Pacific is the deepest of the oceans and has the thinnest crust on its floor of any part of the earth’s surface. In the Pacific, there are not even any submerged highlands around the base of island groups (like the Atlantic Azores). Churchward’s Mu cannot, in short, have existed and there is no room for debate.
There is a greater problem. If the known civilisations of the world descend from a ‘lost’ civilisation that formerly existed on a continent now covered by the ocean or on a continental shelf drowned by rising sea levels, there is a legitimate question that can be asked. Where did this earlier, hitherto unknown civilisation come from? Donnelly, Hancock and their kind see the origins of humanity’s diverse civilisations as problematical and need an earlier prototype to account for those civilisations we do know about, following diffusionist logic. This then begs the question of how and why this ‘lost’ civilisation developed. Unless, of course, you believe that civilisation came from beyond earth…