THE hydrosphere in physical geography describes total mass of water found on low and on surface of the planet. Total mass of hydrosphere of Earth is about 1.4 × 1018 tonnes, which is about 0.023% of total mass of Earth. About 20 × 1,012 tonnes of this is in Earth's atmosphere (volume of one tonne of water is about 1 cubic meter). Approximately 75% of Earth's surface, an area of some 361 million square kilometers (139.5 million square miles) is covered by ocean. Average salinity of oceans on Earth is about 35 ...