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Earth^49

5. EXOSPHERE
   Situated 450–900 km
   (280–560 miles) above the
   Earth’s surface, the exosphere
   is the atmosphere’s outer
   layer, on the edge of space.


6. THERMOSPHERE
   The thermosphere extends
   80–450 km (50–280 miles)
   into space and contains
   the ionosphere, a layer of
   electrically charged particles
   from which radio waves for
   communications can be
   bounced back to the Earth.


7. MESOSPHERE
   The mesosphere lies 50–80 km
   (30–50 miles) above the
   Earth’s surface. Meteors
   (fragments of rock and dust
   from space) mostly burn up
   here, creating shooting stars.


8. STRATOSPHERE
   Lying 12–50 km (7–30 miles)
   above the Earth’s surface, the
   stratosphere is a calm layer
   above the winds and weather.
   The lower stratosphere
   contains the ozone layer.


9. TROPOSPHERE
   Extending to about 12 km
   (7 miles) into space, the
   troposphere contains 75 per
   cent of the air and water in
   the atmosphere.

Most life on Earth depends on the atmosphere, a layer of gases around

our planet. This layer, extending about 700 km (430 miles) into space,

protects us from meteorites and warms the Earth’s surface. It includes

the. OZONE LAYER, which shields us from the Sun’s harmful rays.

A layer of ozone gas in the stratosphere protects us from harmful

ultraviolet (UV) rays in sunlight. UV rays can cause skin cancer,

eye damage, and other health problems in humans and animals.

In the 1980s, scientists discovered that the ozone layer is getting

thinner and that so-called “holes” (areas containing less ozone)

were appearing over Antarctica and the Arctic each spring.

DOES THE ATMOSPHERE REMAIN

THE SAME FROM EARTH TO SPACE?

The Earth’s atmosphere contains five main

layers – the troposphere, stratosphere, mesosphere,

thermosphere, and exosphere. The main gases in the

atmosphere are nitrogen (78 per cent) and oxygen

(21 per cent). There are also small amounts of argon,

carbon dioxide, and water vapour.

WHAT IS CAUSING HOLES IN THE OZONE LAYER?

Chemicals called CFCs (chlorofluorocarbons), used

in the manufacture of fridges and aerosol sprays,

are causing the holes in the ozone layer. CFCs collect

in the upper atmosphere, where they destroy ozone.

During the 1990s, the holes steadily got bigger. Most

countries have now stopped using CFCs, which should

prevent the damage getting worse.

WHAT IS ATMOSPHERIC PRESSURE?

Atmospheric (air) pressure is the force produced by

air as it pushes against its surroundings. This force

is over 1 kg per sq cm (14 lb per sq in). We cannot

feel it, however, because the air presses evenly from

all directions, and our body fluids press outwards.

Air pressure is greatest at sea level and decreases

with altitude.

OZONE LOSS 3

The hole over

Antarctica is

shown in this false-

colour image of

Earth taken by

satellite. Yellow

indicates the thinnest

ozone covering, blue

indicates the thickest.

OZONE LAYER

Atmosphere

Dark cloudtops silhouetted against

light from the setting Sun mark the

edge of the troposphere – the layer

in which the Earth’s weather occurs

The ozone hole

as recorded in September

2000, measured

28 million sq km

(11 million sq miles)

Antarctica shown

here in dark yellow

beneath the ozone

hole in pale yellow

Thinner, dust-free air higher in the

Earth’s atmosphere appears blue

Dense, dusty air in

the lower part of the

atmosphere appears red

FIVE ATMOSPHERE LAYERS

4

2

1

Sun

5

3

FIND OUT MORE. Human Impact 64–65 • Space 10 • Weather 50

atmosphere