African rift valleys were formed by the separation of tectonic plates. Water flows down to the valley floors, creating rivers and lakes.
Dr. John Shea demonstrates the two main principles in the study of rock layers: superposition and association.
Continents rose in elevation after ice sheets from the last ice age retreated. This suggested that the underlying mantle is pliable.
The concept that continents float on a pliable mantle is an important element of the theory of continental drift.
Watch this 30-second tour of how EarthViewer works and how to use the interface.