ATMOSPHERE
The earth is enveloped by the vast ocean of air.This vast ocean is named as atmosphere.
.It is divided into two groups of constituents:
1. Permanent constituents
2. Variable constituents.
PERMANENT CONSTITUENTS
The permanent constituents are :
1. Nitrogen 78%
2. Oxygen 21%
3. Argon 0.93%
4. Carbon dioxide 0.03%
5. Helium, Hydrogen, Neon etc 0.04%
VARIABLE CONTITUENTS
The variable constituents are in the three ststes of matter i.e solids, liquids and gases.
1. Solid: It includes dust, salt and volcanic ash.
2. liquid: Water in the form of water vapour.
3.Gaseous: All kinds of gases.
STRUCTURE OF ATMOSPHERE
The atmosphere is divided into four layers.
1.TROPOSPHERE
It is the lowest layer of atmosphere which touches the earth's surface.Tropospher is the layer in which we live.It is filled with 90% of water vapour, clouds and dust.
The height of this layer varies from equator to the poles.Its height is about 17 km from the equator. In north and south areas of equator ,its height is about 12 km.At the poles it is between 6 to 8 km.The temprature of troposphere decreases with increase in altitude.The temperature drops about 6.5% after every km above the earth's surface in troposphere.
2.STRATOSPHERE
It extends from troposphere to an altitude of about 50 km.The temprature remains constant in the lower stratosphere and very cold about -60 C*.This zone is safest for flight of planes because it is very still.The ozone layer exists in this zone in a a small amount.Ozone acts as a shield for earth against the UV rays of sun.The zone in which the temperature is highest seperates the stratosphere from the upper layer of atmosphere.
3.MESOSPHERE
It extends from 50 km to 80 km above the surface of earth.The temprature begins to drop sharply in this layer to -100 C' and freezes the water vapour in the air.It protects the earth from meteoroids.
4.THERMOSPHERE
It begins above the mesosphere at the height of 80 km from the earth's surface.The temperature of this layer reaches up to 2000 C*.
.It is further divided into two parts:
1.IONOSPHERE
It is the lower part of thermosphere.It consists of nitrogen and oxygen ions.These ions block the AM radio waves from going out in space and bounce them back towards the earth.
2.EXOSPHERE
It is the upper part of thermosphere.The artificial satellites revolve round the earth in this layer.The exosphere is the last layer before space.
Written by: BRIGHT AQUA
