1. Mechanism of Movement:
* Continental Drift: This theory, proposed by Alfred Wegener in the early 20th century, suggested that continents moved over the Earth's surface. However, it lacked a clear explanation *how* this movement occurred. Wegener proposed the continents plowed through the ocean floor, but this idea was not supported by scientific evidence.
* Plate Tectonics: This theory goes beyond simple movement and explains the mechanism driving it. Plate tectonics states that the Earth's outermost layer (the lithosphere) is broken into large, rigid plates that move and interact with each other. The driving force behind this movement is convection currents within the mantle, a semi-molten layer beneath the crust.
2. Scope of Movement:
* Continental Drift: This theory focused primarily on the movement of continents themselves. It didn't address the movement of the ocean floor.
* Plate Tectonics: This theory recognizes that the Earth's surface is made up of both continental and oceanic plates. It encompasses the movement of both types of plates, providing a more comprehensive understanding of how the Earth's surface is constantly changing.
In summary: Plate tectonics expanded upon the idea of continental drift by providing a mechanism for movement (mantle convection) and by including oceanic plates in its scope.
