The hydrosphere and its parts
The hydrosphere is the Earth’s water shell: oceans and seas, rivers, lakes, swamps, glaciers, groundwater and water vapour in the atmosphere. The ocean covers almost 71 % of the Earth’s surface and holds 96.5 % of the world’s water; its average salinity is 35 ‰ (35 g of salt in 1 kg of water), its average temperature is about +17.5 °C, and its water freezes at –2 °C. Land waters make up only a few per cent of the whole hydrosphere, and most of that is stored in glaciers. River flow depends on climate and relief: where rainfall is heavy there are rivers like the Amazon and the Congo, while in deserts there are only transit rivers such as the Amu Darya, Syr Darya and Nile. Lakes: the largest is the Caspian (about 371–376 thousand km²), the deepest is Baikal (about 1 642 m), followed by Tanganyika (1 470 m); the Aral Sea has shrunk and dried up sharply in recent decades. About 99 % of glacier ice lies in polar regions (Antarctica, Greenland, the Arctic); mountain glaciers form above the snow line, which at the equator runs at 4.5–5 km. Groundwater forms when rain soaks into the crust; layers between impermeable layers form artesian basins.
“Where does water go?”: the class splits into groups, each presenting 3 facts with a diagram about one part of the hydrosphere (ocean, river, glacier, groundwater).