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Water, Carbon and Nitrogen Cycles

The Water Cycle.

What is the Water Cycle?

The water cycle describes the movement of water
through the environment. Water evaporates from the
surface of the sea and moves up into the atmosphere.
Water leaves the atmosphere and falls back into
the sea or falls on to land where some water flows back
into the sea as a river as shown in the picture below.
Some water remains on land either in lakes or reservoirs
or the water becomes frozen and exists as ice or snow.

How does the Water Cycle work?

The water cycle works because of heat from the Sun.
Water evaporates from the surface of the sea as warm air
moves across it. Secondary sources (less important)
of water vapour in the air are volcanoes and animal respiration.
Water vapour in the air condenses into small droplets,
and these droplets form clouds. Water falls from the clouds
onto land, as rain or snow. This is called precipitation.
Water on the land collects in streams, rivers and lakes,
and flows back to the sea, completing the cycle.

Why is the Sea Salty?

Rain and river water erodes rocks, dissolving some of
the material as salts. This is what makes the sea salty.
The composition of the sea today is a balance
between the amount of salt entering the sea from
weathering of rocks and the removal of dissolved salts by
crystallisation (forming rock salt), shell formation by
sea creatures and chemical reactions forming sediments.

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