hydrosphere

Three quarters of the surface of planet Earth is covered by water.


Water takes the form of solid, liquid and gas

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Liquid: Most liquid water is seawater, found in oceans and seas. A small percentage is inland water, which is made up of both surface water (lakes and rivers) and groundwater (underground water layers, known as aquifers).


Water exists in a liquid state between 0 °C and 100 °C.
All liquid water contains some salt, but it can be split into three different types, depending on the salt level:


Fresh water: very low salt content (inland water)Brackish water: moderate salt content (inland water)Salt water: high salt content (seawater)

Solid: Most solid state water exists as snow and ice in the polar ice caps and glaciers. Liquid water freezes below 0 °C and transforms into a solid.

Gas:Water is considered a gas in the form of water vapour. Most water vapour exists in the Earth’s atmosphere as evaporation from surface water. However, it can also come from inside the earth in areas of volcanic activity.

COMPOSITION
Sea water is a mixture of mineral salts: the most common component is sodium chloride (common salt). It also contains a large quantity of magnesium salts.The salt in seawater affects density: water with a higher salt content has a greater density.Seawater temperature depends on depth: temperatures are lower in deeper bodies of water and warmer in shallower areas.

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MOVEMENT

Oceans and seas move and change all the time in a variety of ways:

Waves occur on the surface of the water. They are mainly caused by the wind and can vary in strength.Tide is a regular movement in which the sea level rises and falls. This is caused by the gravitational force of the Sun and the Moon.Ocean currents are horizontal movements of water within seas and oceans. Currents have distinct densities and temperatures. They are important because they redistribute heat and salt to different areas of the Earth.

SURFACE WATER

A marsh is a type of wetland found at the edge of other bodies of water, such as rivers, lakes and the sea. They can be formed of fresh, salt or brackish water and often flood.

A lagoon is a shallow not deep lake that forms on coastlines. Lagoons have at least one inletInlet a narrow inland opening of the coastline from the sea.

A lake is a body of fresh, brackish or salt water. The water in lakes comes from rivers, groundwater or from melted glaciers. Lakes are entirely surrounded by land and are different sizes.

In rivers that flow into the sea, a wide estuary of brackish water can form from sea currents that transport river sediment. Estuaries and nearby coastal areas are often heavily populated by humans .

Water accumulates from rain and groundwater in low-lying areas to form wetlands. Wetlands are often seasonal: a shallow layer of water covers the ground for only part of the year.

In rivers that flow into calm sea, a delta can form. There is no sea current to remove river sediment, so it is able to build up in a triangular shape at the river mouth.

A river is a flowing body of fresh water. Rivers flow into the sea, or into other lakes or rivers and form V-shaped valleys. Rivers are a vital source of water for human beings. They are also used for traditional inland transportation on boats.

GROUNDWATER
Groundwater is water that is stored underground, beneath the surface of the Earth.

GLACIERS
Glaciers are large masses of slow-moving ice.


Glaciers can only exist in areas of the Earth where the temperature is always, or nearly always, below 0°C.

Glaciers move downhill towards the bottom of a hill or slope; downwards very slowly. This is because of their immense weight and the gravity of the Earth. Their movement erodes the original landscape and forms U-shaped valleys..

water cycle

PRECIPITATION

After cloud has formed, water returns to the Earth’s surface as either liquid rain or solid snow and hail.

TRANSPIRATION

This occurs when plants lose water due to evaporation caused by heat from the Sun. The water from this process also becomes part of the atmosphere.

CONDENSATION

Through this process the water vapour produced by evaporation and transpiration rises, cools down, and then turns into clouds.

EVAPORATION

This process involves the Sun heating surface water: the water evaporates, turning into water vapour, which then becomes part of the atmosphere.

SURFACE RUNOFF

When liquid water is on the surface of the Earth it flows across the land. This water forms rivers that eventually return the water to the seas and oceans.

INFILTRATION

This occurs when water penetrates the surface of the Earth and becomes underground runoff.

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