NCERT CLASS 7 CHAPTER 1 youtube link: https://youtu.be/tz2Ar-pln9E

1. COMPOSITION AND STRUCTURE
OF ATMOSPHERE
Class 7
NCERT
Chapter-5

2. INTRODUCTION
• Envelope of air surrounding earth is known as
atmosphere
• Upper limit is about 10,000km from the mean
sea level
• Held to the earth by gravitational pull
• Total weight of the earth’s atmosphere- 500
million tons(approx.)
• 90% of total mass is within 32 km from earth’s
surface

3. COMPOSITION OF THE ATMOSPHERE

4. GREENHOUSE EFFECT & GLOBAL
WARMING
• Carbon dioxide absorbs earth’s heat and prevents it
from getting too cold at night, this phenomena is
greenhouse effect
• Increased carbon dioxide
absorbs more heat thus
raising the earth’s
temperature, this increase
in temperature is known as
global warming

5. STRUCTURE OF ATMOSPHERE

6. TROPOSPHERE
 Up to height of 8km near poles and 18km near
equator
 Temperature decreases with increasing height
@1⁰C per 165m of ascent(normal lapse rate)
 All weather phenomena occur in this layer
 Protects from excessive heat during day and
keeps Earth’s surface warm at night
 Has about 90% of the air in the atmosphere

7. STRATOSPHERE
• Estimated height is about 50km above the mean sea
level
• Almost free from all weather phenomena
• Clouds are almost absent & there is very little
dust/water vapor
• Jet planes fly in lower stratosphere
• Temperature remains constant at lower part(up to
about 20km) and then increases with increasing
altitude
• Lower part of this layer(15-35km) has concentration
of ozone & hence called ozonosphere

8. MESOSPHERE
• Extends from 50km to about 80km above the
mean sea level
• Temperature decreases with height & reaches
about -100⁰C at the height of 80km
• Coldest atmospheric layer
• Meteors burn up in this layer

9. THERMOSPHERE
• 80-100km above the mean sea level
• Temperature increases rapidly with increase in
height. Reaches more than 1500⁰C
• Lower part is called Ionosphere, as it has
ionized molecules
• This layer reflects low frequency radio waves
back to the Earth. Thus helps in long distance
communication

10. EXOSPHERE
• Uppermost layer
• Density of air is very low
• Very light gases like hydrogen and helium are
found here
• Temperature increases with height, may
reach up to 4500⁰C
• Merges gradually in to outer space

11. SIGNIFICANCE OF ATMOSPHERE
• Lower has life giving Oxygen, which is needed for life
• Nitrogen and Carbon dioxide are needed by plants for
growth
• Prevents sun’s harmful rays from reaching the surface
• Softens sun’s glare during the day
• Change of weather & climate is due to atmosphere
• Sound waves travel through air
• Shields us from meteors
• Presence of water vapor causes precipitation and
condensation