2.  The envelope of gases and water vapour
surrounding the planet earth is called
atmosphere.
 Atmosphere is divided into several
layers.
 Each layer has its own altitude and
temperature.

3. Layers of the
atmosphere:
There are four
layers of the
atmosphere.
 Trposphere
 Stratosphere
 Mesophere
 Thermosphere
• Ionosphere
• Exosphere

5.  The atmospheric layer closest to the Earth’s
surface is called troposphere.
 Tropo- means “turning” or “changing”.
 Conditions in the troposphere are more
variable than in the other layers.
 It extends to about 12km above Earth’s
surface.
 Troposphere contains 75-80% of the
atmosphere. It is the layer of atmosphere in
which we live.

6.  Nearly all dust particles and water vapours are
in the troposphere.
 Weather occurs in this layer.
 Most of the clouds are formed in the
troposphere.
 Air crafts fly in this region.
 As altitude increases in the troposphere, the
temperature decreases and varies from 17
degree centigrade to -55 degree centigrade.
 On average, for every 1km increase in altitude,
the air gets about 6.5 degree centigrade cooler.

8.  The second layer as one moves upward from
the Earth’s surface is called stratosphere.
 The stratosphere extends from top of the
troposphere to about 50km above Earth’s
surface.
 Strato- means “layer” or “spread out”.
 The lower stratosphere is cold about -55 degree
centigrade but the upper layer is stratosphere is
warmer than the lower stratosphere (-55 to 5C).
 It contains little water vapours and the
miximum amount of ozone layer.

10.  The Ozone layer or ozone shield is an allotropic
form of oxygen.
 It is present in the Earth’s stratosphere and
absorbs most of the sun’s ultraviolet (UV)
radiations.
 It protects the living things on the Earth from
dangerous ultraviolet radiations from the sun.
 Human activity releases many compounds in
the atmosphere. Such compounds threaten the
stability of ozone layer.

11.  The region in which the amount of ozone has
been reduced is called as ozone hole.

13.  The mesosphere extends from the top of
stratosphere to about 80km from the Earth’s
surface.
 Meso- means middle, so the mesosphere is the
middle layer of the atmosphere.
 In the outer mesosphere, temperature
approaches -93 degree centigrade.
 This layer protect the Earth’s surface from
being hit by most meteroids.

14.  The outermost layer of the atmosphere is the
thermosphere.
 It extends from 80km above Earth’s surface
outward into space.
 Thermo means heat.
 This layer is very hot up to 1800 degree
centigrade this is because sunlight strikes it
first.
 It is further divided into two layers.

15.  The lower layer of thermosphere is called the
Ionosphere.
 It extends from 80 to 400km above the Earth’s
surface.
 The outer layer of thermosphere is called the
Exosphere.
 It extends from 400km to thousands of
kilometers from the Earth’s surface.

16.  In the northern hemisphere, brilliant light
displays, occur in the ionosphere. These light
displays are called Aurora borealis. Auroras
are caused by particles from the sun that enter
the ionosphere near the poles. These particles
strike the atoms in ionosphere, causing them to
glow.