51
Atmosphere
Without the atmosphere, it would be
impossible to live on earth. the atmosphere
forms a layer, like a blanket around
earth, protecting us from dangerous
rays from the sun and from the
cold of outer space. it
contains the air that we
breathe, together with
water vapor and tiny
pieces of dust. air
contains the gases oxygen,
carbon dioxide, and nitrogen,
which are necessary for life;
water vapor forms the clouds
that bring rain. the atmosphere
is held by the pull of earth’s gravity
and spreads out to about 1,250 miles
(2,000 km) above earth. three quarters
of the air in the atmosphere lies beneath
35,000 ft (10,700 m) because the air gets
thinner higher up. the air at the top of mount
everest is only one-third as thick as it is at sea level.
that is why mountain climbers carry an air supply
and why high-flying aircraft are sealed and have air
pumped into them.There is no definite upper limit
to the atmosphere. The final layer
before outer space is called the
exosphere; it contains hardly any
air at all.The mesosphere extends from
30 to 50 miles (50 to 80 km)
above Earth. If meteors fall into
this layer, they burn up, causing
shooting stars.Under the mesosphere lies the
stratosphere. It extends from 7 to
30 miles (11 to 50 km) up. The
stratosphere is a calm region.
Airliners fly here to avoid the
winds and weather lower down.Although it is the narrowest layer,
the troposphere contains most
of the gas in the atmosphere. It
reaches about 7 miles (11 km)
above the ground, but this
varies around the globe
and from season to season.
Most weather occurs in
the troposphere.Layers of the
atmosphere
earth’s atmosphere is
divided into several layers.
the main layers, from the bottom
upward, are called the troposphere,
the stratosphere, the mesosphere,
the thermosphere, and the exosphere.sky and sunset
When light travels through the atmosphere,
it hits gas molecules and tiny particles such
as pollen and dust. this causes the light to
scatter, or bounce off, in all directions.
some colors are scattered more than others.BLue sky
the atmosphere scatters mainly blue light; this
is why the sky looks blue. the other colors of
light are scattered much less than blue so that
they come to earth directly. this causes the
area of sky around the sun to look yellow.Compared to the
size of Earth,
the atmosphere
forms a very
narrow band—
approximately
equivalent to the
skin around an orange.other atmospheres
ozone Layer
Within the stratosphere, there is a thin
layer of the gas ozone. ozone is a form of
oxygen that absorbs ultraviolet rays from the
sun. Without the ozone layer, these rays would
reach the ground and kill all living creatures.
pollution and the use of certain chemicals are
destroying the ozone layer.A layer of very thin air called the
thermosphere extends from about
50 to 300 miles (80 to 480 km)
above the ground. It contains the
ionosphere—layers of electrically
charged particles, from which
radio waves can be bounced
around the world.sunset and sunrise
at sunset and sunrise, when the sun is below the horizon,
the light travels through much more of the atmosphere
before we see it. the blue light is scattered so much that it
is absorbed, or soaked up, by the atmosphere. only red
light reaches us, so the sky looks red.other planets’ atmospheres are
very different from earth’s.
neptune (above) is surrounded
by a thick layer of hydrogen and
helium. a small amount of
methane gas in this atmosphere
makes neptune look blue.Find out more
Climates
oxygen
planets
sun
WeatherUS_051_Atmosphere.indd 51 29/01/16 10:29 am