D:\M J\Sanjit pers\4kids\httpdocs\sidebar.html
|The Earth has a
moderately dense atmosphere and usually half of its surface is covered with
clouds. The atmosphere extends hundreds of miles upwards. The higher we go, the
thinner it becomes. It is, in fact, a mixture of many gases and water vapor.
Atmosphere exists in different layers. Different layers have different properties.
The lowest layer,
called troposphere, contains all phenomena that make up our weather. It extends up to about 50 km from
the surface. There is around 78 per cent
nitrogen, 21 per cent oxygen, and minor percentage of argon, carbon
dioxide, neon, helium and methane.
Above this, there is stratosphere. It is made up of lighter oxygen and ozone,
helium and hydrogen. Here the air is always clear and pure. Though its lower part is cold,
higher up it is unbearably hot.
In its uppermost reaches, called ionosphere, the atmosphere is charged with subatomic particles. Even the
charged particles reflect the radio waves.
Without it we would not have long-distance radio communication.
Especially when there was no artificial satellite.
While oxygen is must for a life to live on, each of the gases in the mixture has a role to play. The plants
need carbon dioxide, a part of the mixture,
for making their food. Nitrogen is also required by some plants. Ozone absorbs
most of the very harmful ultraviolet
rays from the Sun. Thus the living
organisms are saved from the extinction.
Water vapor is present in the lower atmosphere, say up to 12 km. Though its amount is
small, but its importance is very great. For, without it, there would be no water on
Earth. Water enters the atmosphere by evaporation from the hydrosphere. It leaves the
atmosphere by a process called precipitations, either as rain or snow.
Clouds are made of water vapor that has evaporated
from the Earth. They are very tiny droplets
of microscopic size and are too light to fall down as rain. So they ride on the air
waves until they condense and then fall down as rain. Its like a never ending
two way traffic. For, the day it stops all our life will be in danger. With all these, the atmosphere protects us from meteors and radiation and supplies the gases for the plants and animals to live on.
And it is the Earth's gravity that binds the
atmosphere to the surface. Gravity, as we know, is the force with which Earth pulls
everything on or near the surface towards its center. Due to this gravity we can all talk
and listen, walk and run, gulp and gobble up and carry outo a plenty of necessary activities. Moon,
the Earth's solitary satellite, also has gravity. But it's too weak to hold much air, save
some traces of gases.
So, not just the atmosphere, or the gravity. Things with the Earth are so finely balanced
that they just rightly serve our purpose. Nothing more. Nothing less