Source:VII NCERT Geography Chapter 5
- Terrarium:It is an artificial enclosure for keeping small house plants.
- The process by which water continually changes its form and circulates between oceans, atmosphere and land is known as the water cycle.
- Three-fourth of the earth surface is covered by water.
- Salinity is the amount of salt in grams present in 1000 grams of water. The average salinity of the oceans is 35 parts per thousand.
- Dead sea in Israel has salinity of 340 grams per litre of water . Swimmers can float in it because the increased salt content makes it dense.
- March 22 is celebrated as World Water Day.
- When the water on the surface of the ocean rises and falls alternately, they are called waves.
- Waves are formed when winds scrape across the ocean surface. The stronger the wind blows, the bigger the wave becomes.
- The rhythmic rise and fall of ocean water twice in a day is called a tide.
- The strong gravitational pull exerted by the sun and the moon on the earth’s surface causes the tides.
- During the full moon and new moon days, the sun, the moon and the earth are in the same line and the tides are highest. These tides are called spring tides.
- The moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of sun and earth resulting in low tides. These tides are called neap tides.
- High tides help in navigation.
- They raise the water level close to the shores.
- This helps the ships to arrive at the harbour more easily.
- The high tides also help in fishing. Many more fish come closer to the shore during the high tide. This enables fishermen to get a plentiful catch.
- The rise and fall of water due to tides is being used to generate electricity in some places.
- Ocean currents are streams of water flowing constantly on the ocean surface in definite directions.
- The ocean currents may be warm or cold.
- The warm ocean currents originate near the equator and move towards the poles.
- The cold currents carry water from polar or higher latitudes to tropical or lower latitudes.
- The Labrador Ocean current is cold current while the Gulf Stream is a warm current.
- The areas where the warm and cold currents meet provide the best fishing grounds of the world. Seas around Japan and the eastern coast of North America are such examples.