3
KEY CONCEPTS
3. Water on the Earth
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The oceans and seas
❚
The oceans and seas cover two-thirds of the Earth’s surface. The
oceans are the
Atlantic
, the
Pacific
, the
Indian
, the
Arctic
and the
Antarctic.
❚
The movements of the water in the seas and oceans are
ocean
currents
,
tides
and
waves
.
Continental waters
❚
Continental waters are rivers, lakes, underground
water and glaciers.
❚
Rivers
are continuous currents of water.
❚
Underground water
is created by enormous
deposits under the Earth’s surface, called aquifers.
Water is extracted from wells.
❚
Lakes
are large bodies of permanent still water.
❚
Glaciers
are large bodies of ice that cover the polar
regions and mountain summits.
The importance of rivers and seas for humans
❚
Rivers
were fundamental in the development of the
first civilisations.
❚
Most major
cities
are located next to a
river.
❚
The
seas
are important
means of communication
and provide
important resources for the
development
of human societies.
Risks and dangers related to water
❚
Both the scarcity and the excess of water can cause
disasters
(
floods
and
droughts
).
❚
Floods can cause serious damage to towns, villages and crops. An
extended drought can cause the death of people and animals and
the disappearance of vegetation.
❚
All the water on the Earth makes up the
hydrosphere.
❚
Most of the water on Earth is in a
liquid state,
but it also appears in the form of
vapour, ice
and
snow.
❚
Most of the water on Earth is
salt water
and
is found in the
oceans
and
seas.
❚
Fresh water
is an essential for animal and
plant
life,
but it is only 3% of the total water
on Earth.
❚
Rivers
hold a very small percentage of the
surface water on Earth. As rivers provide the
water we consume, it is essential that we
keep them in good condition, without
polluting them, and that we use this scarce
resource responsibly.
WATER ON THE EARTH
