Final answer:
The plates between South America and Africa have been moving apart due to continental drift, with new oceanic crust forming at the mid-Atlantic ridge as a result of mantle convection.
Step-by-step explanation:
The tectonic plates between South America and Africa have been moving apart through the process of continental drift, powered by mantle convection. Heat from the Earth's interior causes the mantle to circulate, thus moving the plates. Over time, this movement has caused the Atlantic Ocean to widen as new material is added at the mid-Atlantic ridge.
Alfred Wegener first proposed the idea of continental drift, noticing that the coasts of the continents appeared to fit together. His hypothesis was ultimately confirmed by evidence such as matching geological formations and fossil records across continents, as well as the discovery of the mid-Atlantic ridge and the symmetrical pattern of the Earth’s magnetic field reversals on either side of it. This process is a fundamental concept in geology, similar to evolution in biology or gravity in physics, and represents Earth's mechanism to cool down its interior.