Hydrosphere

The hydrosphere is the combined mass of <a href="/facts/Water/0lkXnJPK">water</a> found on, under, and above the <a href="/facts/Planetary_surface/c3QVcQpV">surface</a> of a <a href="/facts/Planet/rbPjE6Bx">planet</a>, <a href="/facts/Minor_planet/GxoaU532">minor planet</a>, or <a href="/facts/Natural_satellite/AE4KQKbq">natural satellite</a>. Although <a href="/facts/Earth/HLLmDfj0">Earth</a>'s hydrosphere has been around for about 4 billion years, it continues to change in shape. This is caused by <a href="/facts/Seafloor_spreading/2t2oCbTp">seafloor spreading</a> and <a href="/facts/Continental_drift/o7Nfr101">continental drift</a>, which rearranges the land and ocean.
It has been estimated that there are 1.386 billion <a href="/facts/Cubic_kilometer/GPILKCtm">cubic</a> kilometres (333 million cubic miles) of water on Earth. This includes water in gaseous, liquid and frozen forms as soil moisture, <a href="/facts/Groundwater/JYM2IDS2">groundwater</a> and <a href="/facts/Permafrost/SkFC7LMT">permafrost</a> in the <a href="/facts/Earth%2527s_crust/VSy2u31r">Earth's crust</a> (to a depth of 2 km); <a href="/facts/Ocean/8W8lYgjD">oceans</a> and <a href="/facts/List_of_seas/FN5pXXrv">seas</a>, <a href="/facts/Lake/YP0xxn0E">lakes</a>, <a href="/facts/River/GxdjEX21">rivers</a> and <a href="/facts/Stream/S5he7Cuo">streams</a>, <a href="/facts/Wetland/9abbP7CR">wetlands</a>, <a href="/facts/Glacier/8GrKVUSS">glaciers</a>, ice and snow cover on Earth's surface; vapour, droplets and crystals in the air; and part of living plants, animals and unicellular organisms of the biosphere. <a href="/facts/Saline_water/Tgw5AgL8">Saltwater</a> accounts for 97.5% of this amount, whereas <a href="/facts/Fresh_water/xMP2TxwI">fresh water</a> accounts for only 2.5%. Of this fresh water, 68.9% is in the form of <a href="/facts/Ice/BGvkKFjD">ice</a> and permanent snow cover in the Arctic, the Antarctic and mountain <a href="/facts/Glacier/8GrKVUSS">glaciers</a>; 30.8% is in the form of fresh groundwater; and only 0.3% of the fresh water on Earth is in easily accessible lakes, reservoirs and river systems.
The total mass of Earth's hydrosphere is about 1.4 × 1018 <a href="/facts/Tonnes/gMymLmWv">tonnes</a>, which is about 0.023% of Earth's total mass. At any given time, about 2 × 1013 tonnes of this is in the form of <a href="/facts/Water_vapor/DX5IUFG0">water vapor</a> in the <a href="/facts/Atmosphere_of_Earth/FV97Am25">Earth's atmosphere</a> (for practical purposes, 1 cubic metre of water weighs 1 tonne). Approximately 71% of Earth's surface, an area of some 361 million square kilometres (139.5 million square miles), is covered by <a href="/facts/Ocean/8W8lYgjD">ocean</a>. The average <a href="/facts/Salinity/X6mB1YAM">salinity</a> of Earth's oceans is about 35 grams of <a href="/facts/Salt/SCplalQ3">salt</a> per kilogram of sea water (3.5%).

Hydrosphere open-in-new

Hydrosphere