Salt water covers more than seven-tenths of the Earth's surface. We now know that there are high mountains, deep trenches and volcanoes hidden from sight under the waves.
The Pacific, the biggest ocean, is larger than all of the Earth's land area added together. It covers about 166,241,000 sq km
( 64,186,000 sq miles ).The deepest place in the sea is in the Marianas Trench in the Pacific. The water there is 11,033 m ( 36,198 ft ) deep.
Ocean Tides and Currents
Tides are rises and falls in the sea level that occur twice every 24 hours, 50 minutes. They are caused mainly by the moon. When the moon is overhead, its gravity pulls the water towards it, making the seas bulge.
Currents move water about and it is never quite still, even in the deepest ocean. Surface currents, mainly caused by winds, affect only about the top 350 m
( 1,148 ft ) of water. Warm surface currents flow from the Equator towards the Poles, while deep cold polar ones move the other way. The warm Gulf Stream, flowing across the Atlantic, brings mild winters to northern Europe and Iceland.