Composition and Structure of the Atmosphere

Answer the following questions

Question 1

What is the significance of atmosphere?

Answer

The significance of atmosphere can be summarised as follows:

1. It maintains the temperature of the Earth by trapping the heat of solar radiation.
2. It provides us important gases like Oxygen (needed for respiration), Nitrogen (cell formation) and Carbon dioxide (keeps the earth warm).
3. It absorbs ultraviolet solar radiation.
4. Atmosphere exerts pressure which balances internal pressure of organisms.

Question 2

State the components of the atmosphere.

Answer

The Earth's atmosphere consists of a mixture of various gases surrounding the Earth. It is an envelope of gases encompassing the Earth, held by gravity. Two main gases Nitrogen (78%) and Oxygen (21%), make up about 99% of the clean dry air. The remaining gases are almost inert and constitute about 1% of atmosphere. Out of this 1%, Argon is 0.93%. The atmosphere also contains water vapour and dust particles.

Question 3

Name the different layers of the atmosphere.

Answer

The atmosphere consists of four layers:

1. Troposphere
2. Stratosphere
3. Ionosphere
4. Exosphere

Question 4

State the important characteristics of each of the layers.

Answer

Troposphere

1. It is the lowermost atmospheric layer. Under normal conditions, the height of the troposphere is about 8 km at the Poles and about 18 km at the Equator.
2. All weather phenomena takes place in this layer.
3. In addition to pure air, it contains water vapour and dust.
4. There is decrease in temperature with increasing altitude at the rate of 6.4° C per km in troposphere.
5. Tropopause marks the upper boundary of troposphere.

Stratosphere

1. The lower most limit of stratosphere is at tropopause. It extends from 18 to 80 km.
2. It is free from water vapour and dust.
3. Temperature does not change with altitude. In certain situations slight increase in temperature (with elevation) may be noticed.
4. No weather phenomena is seen accept Cirrus cloud formation in lower part.
5. It has Ozone layer. There is a maximum concentration of ozone, a vital gas between 20-30 km.

Ionosphere

1. Ionosphere extends from 80 km to about 480 km.
2. The ionisation of molecules and atoms occurs mainly as a result of ultraviolet rays, X-rays and gamma rays.
3. The temperature decreases with increase in elevation until a low point of -100℃ is reached. Beyond this level, the temperature increases again as a result of absorption of short wave solar radiation by the atoms of oxygen.
4. Nitrogen in the extremely rarified air of ionosphere.
5. Ionosphere reflects low frequency radio waves, but absorbs medium and high frequency waves, making it especially important in long distance radio communication.

Exosphere

1. It is the outermost layer of atmosphere.
2. It contains rarified Hydrogen and Helium gases.

Question 5

What is the significance of atmosphere for the Earth?

Answer

Following are the importance of atmosphere for the Earth:

1. It maintains the temperature of the Earth by trapping the heat, due to presence of Carbon dioxide.
2. It provides us important gases like Oxygen (needed for respiration), Nitrogen (cell formation) and Carbon dioxide (keeps the earth warm).
3. It absorbs ultraviolet solar radiation due to presence of Ozone layer.
4. All the weather phenomena occurs in atmosphere.
5. It is responsible for cloud formation and precipitation which is necessary for water cycle.
6. The Earth is protected by falling meteors as they burn to ash due to friction in atmosphere.

Question 6

What are the properties of Troposphere?

Answer

Following are the properties of Troposphere:

1. It is lower most atmospheric layer with 14 km average thickness. Its thickness is about 8 km at poles and 18 km at equator.
2. All weather phenomena like cloud formation, precipitation, fog etc. takes place in this layer.
3. In addition to pure air, it contains water vapour and dust.
4. There is decrease in temperature with increasing altitude at the rate of 6.4° C per km in troposphere.
5. Tropopause marks the upper boundary of troposphere.

Question 7

What is Tropopause?

Answer

It is the boundary in the Earth's atmosphere between the troposphere and the stratosphere. It lies, on an average, at 17 kilometres above equatorial regions, and about 9 kilometres over the poles.

Question 8

What is the significance of ozone in the atmosphere?

Answer

The significance of ozone layer is that it absorbs the harmful ultraviolet rays coming from the Sun. In the absence of the ozone layer found in the atmosphere and in the event of ultraviolet rays reaching Earth's surface, our planet would have been unfit for human habitation and other living beings.

Question 9

What are the causes of destruction of ozone layer?

Answer

The causes of destruction of ozone layer are:

1. Emission of Nitrogen Oxide by a large number of supersonic transport aeroplanes may cause deterioration of ozone layer.
2. Release of synthetic chemicals primarily Chlorofluoro-carbons(CFCs) into the atmosphere is the most important cause of destruction of ozone layer.

Question 10

Give the properties of Ionosphere.

Answer

Ionosphere

1. Ionosphere extends from 80 km to about 480 km.
2. The ionisation of molecules and atoms occurs mainly as a result of ultraviolet rays, X-rays and gama rays.
3. The temperature decreases with increase in elevation until a low point of -100℃ is reached. Beyond this level, the temperature increases again as a result of absorption of short wave solar radiation by the atoms of oxygen.
4. Nitrogen in the extremely rarified air of ionosphere.
5. Ionosphere reflects low frequency radio waves, but absorbs medium and high frequency waves, making it especially important in long distance radio communication.

Question 11

What is meant by Greenhouse Effect?

Answer

The process whereby radioactively active gases absorb and delay the loss of heat to space, thus keeping the lower troposphere moderately warmed throughout the radiation and radiation of infrared wavelengths is called Greenhouse Effect. It leads to gradual increase in the temperature of Earth. The gases responsible for Greenhouse effect are carbon dioxide, methane and CFCs.

Question 12

What do you mean by 'Global Warming'? What are the consequences of 'Global Warming'?

Answer

The gradual increase in average temperature of the Earth and change in climate pattern is called Global warming. It occurs due to greenhouse effect of gases like carbon dioxide, methane and CFCs.

The consequences of 'Global Warming' are:

1. Melting of ice caps and Glaciers.
2. Increasing sea temperature is wiping out coral reefs. These are breeding ground for many marine species and they protect coastlines from storms.
3. It may pose serious threat to the ecological balance.
4. Higher wildlife extinction rates.
5. Higher sea levels.
6. Global warming is increasing the frequency and severity of many types of disasters, including storms, heat waves, floods, and droughts.

Question 13

Name a few measures that could be taken to save the ozone layer.

Answer

A few measures that could be taken to save the ozone layer are:

1. Minimize the emission of gases that are harmful for Ozone layer such as nitrogen oxide.
2. Minimize the continuous release of synthetic chemicals primarily chlorofluoro-carbons (CFCs) into the atmosphere.
3. Worldwide awareness against the use of Chloro-fluoro carbons.
4. Illegal trade of harmful chemicals must be controlled.
5. Finally, take strict decision to ban the use of harmful chemicals and invent alternatives to these chemicals.

Question 14

Name the three realms of the Earth.

Answer

Three realms of earth are:

1. Lithosphere
2. Hydrosphere
3. Atmosphere.

Question 15

State the composition of the Earth's atmosphere.

Answer

The atmosphere consists of a number of gases like Nitrogen (78%), Oxygen (21%), Carbon dioxide and other gases like Argon, Helium etc. In addition to these gases, the atmosphere also contains water vapour and dust particles.

Question 16

How can we reduce global warming?

Answer

Following are the steps that can be taken to reduce global warming:

1. Conservation of forests and control indescriminate felling of trees
2. Reduce industrial and vehicular pollution.
3. Control the release of chlorofluoro carbons in atmosphere.
4. Reduce the release of green house gases like carbon dioxide and methane.
5. Create awareness regarding pollution and its effects.

Define the following terms

Question 1

Troposphere

Answer

The lowest and densest layer of Earth's atmosphere, with average height of 14 km, which is the site of all weather phenomena is known as troposphere.

Question 2

Stratosphere

Answer

The layer of atmosphere extending from 18 to 80 km, which lies between troposphere and mesosphere is called Stratosphere.

Question 3

Weather

Answer

The atmospheric conditions like temperature, precipitation, wind and humidity etc. prevailing at a particular place and time is known as weather.

Question 4

Greenhouse Effect

Answer

The process whereby radioactively active gases absorb and delay the loss of heat to space, thus keeping the lower troposphere moderately warmed throughout the radiation and radiation of infrared wavelengths is called Greenhouse Effect.

Question 5

CFC

Answer

CFC stands for Chlorofluorocarbons. They are synthetic industrial chemical compounds containing Chlorine, Fluorine and Carbon atoms. These are used as cleaning agents, in refrigerators, fire extinguishing fluids, spray, car propellants and insulating foams. They cause deterioration of Ozone layer.

Question 6

Thermosphere

Answer

Atmospheric layer, about 400 km thick, lying above mesosphere which has upwardly increasing temperature is called thermosphere.

Distinguish between the following

Question 1

Troposphere and Stratosphere

Answer

Question 2

Stratosphere and Thermosphere

Answer

Give reasons for the followings

Question 1

The layer of the atmosphere become thinner with altitude.

Answer

The gravity causes the upper layers of atmosphere to exert pressure on the lower ones due to their weight. This causes the air to compress and hence the air become dense at the lower level while upper layers are thinner.

Question 2

The Earth does not experience extremes of temperature.

Answer

The earth does not experience extremes of temperature as on other planets due to the presence of the atmosphere. The atmosphere absorbs some of the heat of the sun, and the remainder is reflected back. As a result, the planet doesn't become too heated during the day or too cold during the night.

Question 3

Solid particles play an important role in the atmosphere.

Answer

Solid particles are important because they serve as nuclear centres around which the water vapour condenses to form cloud particles.

Question 4

The presence of ozone layer is a boon to human being.

Answer

The ozone layer plays a crucial role in protecting the Earth and its inhabitants from harmful ultraviolet (UV) radiation from the sun. Without the protective barrier provided by the ozone layer, the amount of UV radiation reaching the Earth's surface would be much higher and our planet would have been unfit for human habitation and other living beings. Thus, presence of ozone layer is a boon to human beings.

Question 5

Ionosphere is important in long distance radio-wave communication.

Answer

Ionosphere reflects low frequency radio waves but absorbs medium and high frequency waves. Thus, this layer is especially important in long distance radio-wave communication.

Diagram

Question 1

Draw a self-explanatory diagram illustrating the structure of the atmosphere.

Answer

Below diagram illustrates the structure of the atmosphere:

Choose the correct option

Question 1

The proportion of Nitrogen in the atmosphere is about

1. 80%
2. 21%
3. 78%
4. 65%

Answer

78%

Question 2

Which of the following is the lower most layer of the atmosphere?

1. Stratosphere
2. Troposphere
3. Ionosphere
4. Exosphere

Answer

Troposphere

Question 3

In which of the following layers in atmosphere, Normal lapse rate of temperature is observed?

1. Stratosphere
2. Troposphere
3. Ionosphere
4. Exosphere

Answer

Troposphere

Question 4

Which of the following layers of atmosphere absorbs the ultra violet rays of Sun?

1. Ozonosphere
2. Troposphere
3. Ionosphere
4. Exosphere

Answer

Ozonosphere

Question 5

............... layer of atmosphere is important for long distance radio communication.

1. Stratosphere
2. Troposphere
3. Ionosphere
4. Exosphere

Answer

Ionosphere

Question 6

Which of the following chemical is responsible for the depletion of ozone?

1. Carbon di Oxide
2. Nitric Acid
3. CFC
4. All the above

Answer

CFC

Question 7

Which one is the outermost layer of atmosphere?

1. Ionosphere
2. Stratosphere
3. Exosphere
4. Troposphere

Answer

Exosphere

Question 8

Which of the following is not a reason for global warming?

1. Rise in the sea level
2. Ozone depletion
3. Deforestation
4. Burning of fossil fuel

Answer

Rise in the sea level

Question 9

Different types of weather phenomena is seen in

1. Ionosphere
2. Stratosphere
3. Exosphere
4. Troposphere

Answer

Troposphere

Question 10

Which of the following is not a greenhouse gas?

1. Ozone
2. CO₂
3. Helium
4. Methane

Answer

Helium