The hydrosphere is defined as the total mass of water found on, beneath, and above the surface of a planet, minor planet, or natural satellite. Despite the fact that the Earth’s hydrosphere has been existing for roughly 4 billion years, it is still changing shape. This is created by seafloor spreading and continental drift, which causes the land and ocean to reorganize.

It is believed that the Earth contains 1.36 billion cubic kilometers (332 million cubic miles) of water. This encompasses both liquid and frozen water in groundwater, seas, lakes, and streams. Fresh water contributes for only 2.5 percent of this total, whereas saltwater accounts for 97.5 percent. 68.9 percent of this fresh water is in the form of ice and permanent snow cover in the Arctic, Antarctic, and mountain glaciers; 30.8 percent is in the form of fresh groundwater; and just 0.3 percent is in conveniently accessible lakes, reservoirs, and river systems.

The overall mass of the Earth’s hydrosphere is approximately 1.4 1018 tonnes, or approximately 0.023 percent of the total mass of the Earth. At any one time, around 20 1012 tonnes of this is present in the form of water vapor in the Earth’s atmosphere (for practical purposes, 1 cubic meter of water weighs one tonne). The ocean covers around 71 percent of the Earth’s surface, an area of approximately 361 million square kilometers (139.5 million square miles). The average salinity of the world’s oceans is around 35 grams of salt per kilogram of sea water (3.5 percent ).