Reality → Matter → Earth → Oceans
| Sea salt | |
|---|---|
| chloride | 55% |
| sodium | 31% |
| magnesium | 3.7% |
About 70 % of Earth’s surface is covered by oceans. The average depth of all oceans is about 3,800 m (at scale, this is less than a 0.1 mm thick water film on a basketball). The total volume of the oceans is about 1.4 billion km3 , equivalent to a mass of 1.4 Et (1.4 exatonnes, or 1.4 × 1018 t), representing 0.02 % of Earth’s mass. The average salinity of the oceans is 3.5 %. About 85 % of the dissolved matter is sodium chloride, though traces of practically all elements are believed to be present in sea water [1] . The oceans harbor a large amount of marine life in very diverse forms [2] .
Sea salt is believed to contain soluble compounds of all elements that occur on land, brought into the oceans by rivers, land erosion and volcanism. The concentration of most elements would be too low for normal detection. The extraordinary accumulation of sodium chloride can be explained by its high solubility.
Marine life ranges from bacteria to whales, the largest animals on Earth. Life has even been detected in abysses more than 10 000 m deep, an environment of tremendous pressure and no light. The volume of the oceans is several hundred times the volume of the terrestrial habitable zone, but the share of marine life's contribution to total biomass is unknown. Quantity and diversity of marine life are threatened by overfishing and pollution.