Scientists believe that is an example of an internal force that changes the earth’s crust.

Scientists believe that plate tectonics is an example of an internal force that changes the Earth’s crust.

Plate tectonics is a theory that describes the motion of seven large plates, and many other smaller plates of the Earth's lithosphere. When they collide they can make mountains or we can feel their motion as earthquakes. Their motion is responsible for the continental shift and it made our continents look the way they look today.

since there isn't any suggested answers i will give you the reason and hopefully you can figure it

south africa, or rather all of africa, has not been in the location in which it is nowadays throughout the geological past. after the super-continent pangaea started to break apart, gondwanaland, in which was africa, moved further south, and parts of it came to be very close to the south pole. because the climate in this part of the world is very cold due to the very dispersed sun rays in there, what is now south africa, started to freeze, and the conditions were right for the formation of glaciers. the glaciers existed up until the period when gondwanaland started to break apart and what is now africa started to move towards north, sp it warmed up and the glaciers melted.