Planet Earth is made up of four layers. The solid outer layer or crust (0 to 70 km) lies over the mantle which is a highly viscous layer (70-2890 km) and is composed of silicate rocks rich in iron and magnesium. The mantle surrounds the outer core (2890 - 5150 km) which is less viscous and finally the internal solid core (5150 - 6360 km) of iron and some nickel.
The Earth has not lost its dynamism and processes of crust formation still continue. The lithosphere, a layer composed of the crust and upper mantle, is divided into 12 tectonic plates that slowly move. These movements are the cause of earthquakes and volcanic activity.
The German geologist and meteorologist Alfred L. Wegener (1880-1930) proposed the theory of continental drift in 1915. Unlike other researchers who explained the distribution of plants and animals and their fossils in the world by claiming the existence of old bridges across continents and the disappearance of the famous Atlantis (the lost continent), Wegener brought together a series of observations like a jigsaw puzzle, proposing that the continents had once been joined together in a supercontinent, which he called "Pangea" (from Latin, pan = all, gea = land, all land).