The lithosphere and the origin of continents

The lithosphere consists of the Earth’s crust and the uppermost part of the mantle. The boundary between crust and mantle was found by the Croatian seismologist A. Mohorovicic in 1909 (the textbook says 1914). There are two types of crust: continental crust is 35–40 km thick under plains and 55–70 km under young high mountains (up to 70–80 km in the Himalaya), while oceanic crust is 5–10 km thick and has no granite layer. The stable parts of the crust are platforms (they match plains, with few earthquakes and volcanoes); the very mobile parts are geosynclinal belts (the Pacific “Ring of Fire”, the Himalaya, the Mediterranean). The lithosphere is split into plates; usually seven major plates are named: Pacific, North American, South American, Eurasian, African, Antarctic and Indo-Australian. Mountains, volcanoes and earthquakes occur at plate boundaries. The main land relief forms are mountains and plains; the highest point is Jomolungma (Everest) at 8 849 m (measured as 8 848.86 m in 2020), and one of the lowest land points is the shore of the Dead Sea (about –430 m, its level falling year by year). The ocean floor has the shelf (down to 200 m), the continental slope (bathyal, to 3 000 m), the abyssal zone (to 6 000 m) and deep trenches (deeper than 6 000 m); the deepest place is the Mariana Trench (about 10 935 m).