NOTES

The hydrosphere in physical geography describes the combined mass of water found on, under, and over the surface of a planet.Fresh water accounts for only 2.5%. Of this fresh water 68.7% is in the "form of ice and permanent snow cover in the Arctic, the Antarctic, and in the mountainous regions. Next, 29.9% exists as fresh groundwaters. Only 0.26% of the total amount of fresh waters on the Earth are concentrated in lakes, reservoirs and river systems where they are most easily accessible for our economic needs and absolutely vital for water ecosystems." The total mass of theEarth's hydrosphere is about 1.4 × 1018 tonnes, which is about 0.023% of the Earth's total mass. About 20 × 1012 tonnes of this is in the Earth's atmosphere (the volume of one tonne of water is approximately 1 cubic metre). Approximately 75% of the Earth's surface, an area of some 361 million square kilometers (139.5 million square miles), is covered by ocean. The average salinity of the Earth's oceans is about 35 grams of salt per kilogram of sea water (3.5%)

Water covers more than 70 percent of the Earth's surface and provides vital resources to all organisms on the planet. The largest bodies of water on Earth are the oceans, which consist of saline water, meaning salt water. Though all the oceans on Earth are connected, they have been divided into several sections geographically. The largest bodies of water on Earth are the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean, and Arctic Ocean.

The Pacific Ocean is the largest ocean on Earth, covering more than one-third of the Earth's surface and nearly half of Earth's water surface. The world's second largest ocean is the Atlantic Ocean, which covers one-fifth of the total surface area of the Earth. The third largest ocean in the world, the Indian Ocean, is surrounded by the Arabian Peninsula and Southeast Asia in the north, Africa in west and Australia in the east.

The Southern Ocean has been defined relatively recently, in 2000, and consists of the waters around Antarctica. Located around the Arctic Circle, the Arctic Ocean is the smallest and the shallowest ocean in the world. South China Sea, one of the largest seas after the 5 largest oceans of the world, surrounds hundreds and hundreds of islands.