Many theories have helped Plate Tectonics become what it is today. Here are some of the most important ones:
In ancient times, people believed that gods caused all of the world's natural events. The Japanese thought that earthquakes were the work of the Namazu, or giant catfish. The Romans said that volcanoes were caused by Vulcan, the crippled blacksmith god, working at his forge. The Hawaiian Islanders thought that eruptions were the work of Pele, fire god.
Greek Philosopher, Aristotle (384-322 B.C.), said that the Earth was made up of huge caverns with tunnels that wind flowed through, causing pressure to build up and the Earth to shake.
In the 1600's, people noticed that the coasts of Africa and South America fit together, and blamed the semblance on the Great Deluge (the excess water from Noah's flood).
In the 18th century. There were two main theories about plate tectonics. The first of these two was the Neptunist Idea. This stated that the Earth was made up of a solid core which was surrounded by watery materials. These materials settled, slowly became the rocks on the Earth's surface. This theory conveniently described where all the water on the Earth had come from. The other theory of this time, the Platonist Idea, said that the Earth had a hot interior of molten rock, which erupted onto the surface.
In the Mid-1800's, a scientist by the name of James Dwight Dana, had the theory that the Earth was made up of a hot molten center and that it was slowely cooling.
Sir George Airy had another theory about continents and mountains. He thought that mountains and continents moved like icebergs, floating on top of a sea of magma.
Frank Taylor also had a theory about the placement of the continents. This theory stated that the continents were orginally two large landmasses floating over the North and South poles. South America, Africa, and Australia had their origins in the southern landmass (the one over the South Pole) and the northern landmass had broken apart, forming Europe, Asia, and North America. These continents were slowly moving toward the Equator;caused by the Moon's garvitational pull.
In, 1932, Alfred Wegener, a German Meteorologist, came up with the single most important theory in the formation of the theory of plate tectonics. He formulated the concept of continental drift, this theory simply was that the Earth once was a huge land mass, Pangea. Then it broke apart forming into Gondwanaland and Lauarasia and so on. Continuing in this manner until it formed what is now the 7 continents of the Earth.
In the late 1950's, the theory of Seafloor spreading, stating that everything in the ocean is spreading out from the Mid-Atlantic ridge, was formulated.
In 1968, American earth scientists Bryan L. Isacks, Jack Oliver, Lynn Sykes, combined their ideas and came up with the theory that the plates floated on a soft flowing asthenosphere.
All of these different theories have been expanded and changed until they reached their current form. The whole theory is more of an abstract idea, and not a concrete theory. It is a combination of the theories of continental drift, paleomagnetism, and seafloor spreading. Instead of just saying what is happenning, it more or less describes the movements of plates in the past, the present, and in the future, and the effects thereof.