There is 2.45 times more sea than land on planet Earth.
Sea water is enriched with trace elements and minerals.

Sea water (salt water) accounts for 97 % of the planet’s water resources.
The rest occurs in the form of ice (2 %), fresh water and water vapour (1 %).

Earth is often referred to as the blue planet.
Not surprising, when you consider that 71 % of its surface (an area of 360,700,000 square kilometres) is covered by oceans with an average depth of 3,800 metres. In some parts of the world, the sea can be as much as 11,000 metres deep.

The highest and lowest points of the lithosphere are :

• Mount Everest in the Himalayas, the highest point, at 8,848 metres above sea level,
• the Mariana Trench in the Eastern Pacific, the deepest point on the ocean floor at 11,034 metres.

The total variation between these two extremes is thus 20,000 metres (20 kilometres).

Salts wash into the oceans from rocks and sediments.
Over millions of years, the mineral salts contained in the soil have been dissolved by rain water, leaching into streams and rivers and eventually carried to the oceans (atmospheric route).

The salinity of sea water ranges from 30 to 40 g of salt per litre of sea water.

Salinity is higher in regions where evaporation outstrips rainfall and inflows of fresh water (warm seas, the seas between the tropics) :

• Oceans = 30 to 37 g per litre
• Mediterranean = 36 to 38 g per litre
• Red Sea = 42 to 44 g per litre.

Salinity is lower in seas fed by large volumes of river water (equatorial waters, mid to northerly and southerly latitudes, Baltic and Black Seas) :

• Black Sea = 19 g per litre
• Gulf of Bothnia = 5 g per litre

The Baltic Sea at 2 g per litre and the Red Sea at 44 g per litre can currently be considered the two extremes of salt concentration in open seas.