Composition and Structure of the Atmosphere

A is false but R is true.

Explanation — Jet planes usually fly in the lower part of the Stratosphere, not the Troposphere. This is because this layer is free of water vapour and dust, and no visible weather phenomena takes place in this layer.

Both A and R are true and R is the correct explanation of A.

Explanation — The ice cover is indeed shrinking in regions like the Arctic, Antarctic, Alaska, and Greenland. This is mainly due to rising global temperatures, which are increasing at an alarming rate because of human activities such as burning fossil fuels, deforestation, and industrial pollution. These actions release greenhouse gases that trap heat in the atmosphere, leading to the melting of ice in polar and glacial regions.

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.

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.

The atmosphere consists of four layers:

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Three realms of earth are:

1. Lithosphere
2. Hydrosphere
3. Atmosphere.

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.

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.

78%

Troposphere

Troposphere

Ozonosphere

Ionosphere

CFC

Exosphere

Rise in the sea level

Troposphere

Helium

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.

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

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

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.

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.

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

Below diagram illustrates the structure of the atmosphere:

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.

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.

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

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.

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.

From a geographical perspective, the decline in wheat production in the USA is mainly due to rising temperatures caused by global warming. Even regions in higher latitudes are experiencing warmer climates. Since wheat thrives best in cooler conditions, the increasing heat is negatively affecting its growth, leading to reduced yields.

Both the statements are correct.

Carbon dioxide (CO₂) is a vital greenhouse gas that helps trap heat in the atmosphere, maintaining the Earth’s temperature at a level suitable for life. Without it, the planet would be extremely cold. However, excessive CO₂—mainly due to human activities like burning fossil fuels and deforestation—is causing global warming and disrupting the natural climate balance.

The continuous rise in global temperatures due to climate change is creating environmental conditions that amphibians, like frogs, cannot easily adapt to. These species are highly sensitive to temperature and moisture changes, and as their natural habitats become unsuitable, their survival is at risk leading many of them toward extinction.