3rd Class Science Our Environment Atmosphere

   Atmosphere

Thick envelop of air around the earth is called atmosphere. Air, like other natural resources is very much essential for all kinds of life to survive. We can live without food for many days, without water for few days, but we can't live without air even for few minutes. Air is a mixture of many gases like oxygen, nitrogen, carbon dioxide, argon etc. We inhale oxygen from air. Atmosphere contains 21% oxygen, 78% nitrogen and 1% other gases. Atmosphere extends up to the height of about 120 km above the earth surface.

         Layers of Atmosphere

Atmosphere is divided into mainly 4 layers, Thermosphere, Mesosphere, Stratosphere and Troposphere. Atmosphere has an important role to play in cloud formation and precipitation of rain. Ozone layer present in the stratosphere prevents harmful radiations of the Sun to enter earth surface.

         Properties of Air

Look at the following picture to understand the properties of air:

           Uses of Air

Look at the following picture of the uses of air:

         Atmospheric Pressure

Atmosphere exerts pressure on us, known as atmospheric pressure. Atmospheric pressure decreases as we go higher altitudes. This is because thickness of air decreases as we go up.

         Air Pollution

The presence of undesirable substances in the atmosphere is threat to the life of all kinds. It is known as air pollution. Undesirable substances are called as contaminants or pollutants.

Look at the following picture to understand the causes of air pollution:

           Problems Related to Air Pollution

Air pollution causes many physical and mental problems like respiratory problem, asthma, lung disease, nausea, headache etc. Irritation of skin, allergy are also seen in people living in polluted air zone.  

         Prevention

We can't stop pollution. But by following certain norms we can minimize it.

By conserving our natural resources sensibly, we can keep our environment clean and green. It will be then a safe and suitable place for the survival of all kinds of life form, whether plants or animals.  

     Which one of the following layers of atmosphere prevents ultra violet rays to come into the earth surface?

(a) Troposphere

(b) Stratosphere

(c) Mesosphere

(d) Thermosphere

(e) None of these

Answer: (b)

Explanation

Ozone layer is present in the stratosphere which prevents ultraviolet rays to come into the earth surface. Therefore, option (b) is correct and rest of the options is incorrect.

     Which one of the following is not found in air?

(a) Oxygen

(b) Nitrogen

(c) Diamond

(d) Carbon dioxide

(e) None of these

Answer: (c)

Explanation

Diamond is not found in air. Therefore, option (c) is correct and rest of the options is incorrect.