Unit-1

ENVIRONMENTAL SEGMENTS

Learning Outcomes

Prerequisites

Key Words

Lithosphere, Hydrosphere, Biosphere, Climate, Weather

Discussion

As we all know, the earth is the only planet which has life. Life sustaining elements such as land, water and air are present on the earth. Environmental studies is a multidisciplinary academic field of study which deals with the environment and its functions. The environment is the biotic and abiotic surroundings of an organism or population, and consequently includes the factors that have an influence in their survival, development and evolution. The environment can vary in scale from microscopic to global in extent. Examples include the marine environment, atmospheric environment and the terrestrial environment. The surroundings of a living organism, including natural forces and other living things, pro-vide conditions for development and growth as well as of danger and damage.

This branch of study uses principles from the physical sciences, commerce/economics, the humanities, and social sciences to address complex contemporary environmental issues. Basic principles of subjects such as ethics, geography, anthropology, education, politics, law, economics, philosophy, sociology, pollution control and natural resource management have a vital role in environmental studies.

1.1.1 Environmental Segments

Do you know about the environmental segments controlling life and environmental processes? There are four environmental segments which include

1. Atmosphere
2. Hydrosphere
3. Lithosphere
4. Biosphere

The mutual interactions of these segments are responsible for the dynamic changes and the resultant impacts over the globe.

Any change imposed or occurred in one segment will affect the nature and functioning of the others as well. Elements from each segment are subjected to these dynamic processes and all are inevitable for life.

1.1.1.1 Atmosphere

Atmosphere is the layer of gases surrounding the Earth. This layer is retained over the globe, by the action of earth’s gravity. It contains about 5000 million tons of gases. Among these, there are primary gases present in the atmosphere such as Nitrogen which amounts to 78%, oxygen to 21%, carbon dioxide to 0.33% and argon to 0.93%. The other gases present in the atmosphere are helium, methane, ozone, neon, xenon and many trace gases. Do you think that the above-mentioned gases are present everywhere? Above a height of 50 km from the earth’s surface, atmosphere contains only oxygen, ozone, helium and hydrogen. Atmosphere contains water vapour and the amount of vapour in atmosphere varies with seasons.

The Earth’s atmosphere has evolved into the present condition over a period of geological time and phases. Experts have studied about the evolution of the earth’s atmosphere. The history of the Earth’s atmosphere prior to the past one billion years is poorly understood. Atmosphere had two different compositions earlier. The original atmosphere primarily contained helium and hydrogen. Heat waves which emanated from the molten mass of the earth’s interior and the sun dissipated into this atmosphere. The earth, with all its volcanic eruptions, released steam, carbon dioxide, and ammonia. This created the “second atmosphere”. In this phase, the atmosphere had carbon dioxide and water vapour, with some nitrogen, but virtually no oxygen. This second atmosphere had about 100 times as much gas as the current atmosphere. During the next few billion years, water vapour condensed to form rain and oceans, which began to dissolve carbon dioxide. This was the first aquatic environment which favoured the origin of life. Due to the evolution of life, the levels of oxy-gen increased significantly, lowering the levels of carbon dioxide. With the appearance of an ozone layer (ozone is an allotrope of oxy-gen) life forms were protected from the ultra-violet radiation of the sun. This oxygen-nitro-gen atmosphere is considered to be the “third atmosphere”.

Atmosphere is responsible for:

1. the unequal heating of the earth’s surface by insolation,
2. different heat zones,
3. variation in temperature,
4. changes in atmospheric pressure,
5. origin of winds,
6. formation of clouds, rainfall and snowfall.

Structure of the Atmosphere:

Atmosphere is stratified in the form of layers and is divided into three major layers such as Troposphere, Stratosphere and Ionosphere.

The characteristics of these layers vary in relation to their composition, temperature and impacts of radiation.

Troposphere

The Troposphere is the layer lying just above the surface of the earth. It contains 70% of the mass of the atmosphere. It extends up to 8-18 km. The air in this sphere contains 1% water vapour and more CO2. It is a dusty layer. The fall of temperature in this zone is 1 deg. C per km. The temperature ranges from 150C to –56 0C. The Troposphere is the zone of turbulence, climate and weather. It ends at a zone named tropopause which separates the stratosphere from the troposphere. Hence, most of the pollutants stay in troposphere. Some extremely stable compounds like chlorofluorocarbons (CFCs) do cross into the next layer.

Stratosphere

The Stratosphere is the second layer of the atmosphere. It extends up to 80 km. In this zone, meteors will be visible. In the stratosphere, there is 1000 times less water vapour and 1000 times more ozone than the troposphere. This layer is free from clouds. Most of the aircrafts, go above the clouds and fly through the stratosphere, as there is little turbulence for flying. Hence, this zone is called as the zone of jet planes. In this layer the temperature increases with increase in altitude. from –520C to –20C. This layer ends at a region called stratopause, separating the next higher layer, ie the Ionosphere. The Stratosphere contains ozone layer which protects the life on Earth from the Sun’s ultra violet radiation. Ozone is formed by UV radiation or lightning interaction with O2 molecules. Ozone itself is very harmful to living cells. The Ozone layer depletes due to the emission of chlorofluorocarbons and other harmful gases. Depletion of ozone is the principal cause for sunburn, skin and eye cancers and cataracts.

Mesosphere

Mesosphere zone extends up to 80 km above the stratosphere. The temperature decreases uniformly with height, and it may reach as low as -1000C at places. The pressure is also very low at this zone.

Thermosphere

Above the mesosphere, to a height of 700 km is the thermosphere, where the atmosphere density is extremely low with the temperature increasing rapidly. The temperature at 350 km is 12000C. The inversion of temperature at this height is due to energy extracted from sunlight at wavelengths below 200 nm. This region is characterised by the dissociation of oxygen molecule, ionisation of oxygen atom, oxygen molecule, nitrogen molecule. Due to photoionisation reactions, this region is rich in electrically charged particles and electrons, and hence is also called ionosphere.

Exosphere

The region above the thermosphere upto 10,000 km is termed exosphere. It has only at-oms of hydrogen and helium. It has very high temperature due to solar radiation.

1.1.1.2 Hydrosphere

Can we think of life without water? It is said that water is life. Water is an essential component of all life forms that exist over the surface of the earth. More than 71 per cent of the earth is covered with water. The hydrosphere is a collective term given to all different forms of water. Which are the water resources you have come across? It includes all types of water resources such as oceans, seas, rivers, lakes, streams, reservoirs, glaciers and ground water. Hydrosphere is the total amount of water on a planet. It includes water that is on the surface of the planet, underground and in the air. A planet’s hydrosphere can be liquid, vapour or ice. On the Earth, liquid water exists on the surface in the form of oceans, lakes and rivers. It also exists below ground—as groundwater in wells and aquifers. Water vapour is most visible as clouds and fog. The frozen part of the Earth’s hydrosphere is made of ice: glaciers, ice caps and icebergs. The frozen part of the hydrosphere has its own name, the cryosphere. Water moves through the hydrosphere in a cycle. Water collects in clouds and then falls to the Earth in the form of rain or snow. This water collects in rivers, lakes and oceans. Then it evaporates into the atmosphere to start the cycle all over again. This is called the hydrological cycle. Our earth is called ‘blue planet’ due to the presence of water.

Hydrological Cycle

The hydrological cycle involves a continuous exchange of water between sea, atmosphere, land and living animals through massive evap-oration of water from the ocean, cloud forma-tion and precipitation. The land surface and water surfaces on earth lose water by evaporation and by solar energy. Evaporation of water from the ocean exceeds precipitation by rain into the seas by 10%. This 10% excess which precipitates on land balances the hydrological cycle. Some of the precipitated rain seeps into the soil as ground water. Ground water moves up by capillary action and thereby maintains a continuous supply of water to the surface layer of soil. The water from the surface layer of the soil is absorbed by plants, which in turn is returned to atmosphere through transpiration. Surface water or runoff flows into streams, rivers, lakes and catchment areas or reservoirs. Animals also take water which is also returned to the atmosphere through evaporation. Thus there is always a balanced continuous cycling of water between the earth’s surface and atmosphere.

1.1.1.3 Lithosphere

Apart from air and water, what are the other major segments? The lithosphere is the solid, outer part of the Earth. It comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements which sustain organisms. The lithosphere includes the brittle upper portion of the mantle and the crust, the outermost layers of the Earth’s structure. It is the most rigid of the Earth’s layers. Although the rocks of the lithosphere are still considered elastic, they are not viscous. The litho-sphere is also the coolest of the Earth’s layers.

1.1.1.4 Biosphere

The biosphere refers to the realm of living organisms and their interactions with the environment (viz: atmosphere, hydrosphere and lithosphere). It is very large and complex and is divided into smaller units called ecosystems. The complex of living organisms, their physical environment, and all their inter relationships in a particular unit of space is called the ecosystem. Within each ecosystem there are dynamic inter relationships between living forms and their physical environment. Within the ecosystem, organisms interact with one another and with their physical environment in various ways.

On the basis of this interaction the biotic community can be grouped into the following: –

1. Producers: They are green plants which absorb carbon dioxide, mineral nutrients and water and release oxygen required for other living things on the earth.
2. Consumers: Producers are consumed by herbivorous animals that in turn are consumed by carnivorous animals or the secondary consumers. This establishes a chain known as the food chain.
3. Decomposers: The fecal matter, excreta of animals, plants, humans and other dead organisms are decomposed by the activity of bacterial fungi and other small organism which thrive on decaying organic matter. The de-composers are important because they bring the constituent elements of plants and animal bodies back to the surrounding medium or soil.

Concepts of Weather and Climate

There are many components to weather. Weather includes sunshine, rain, cloud cover, winds, hail, snow, sleet, freezing rain, flooding, blizzards, ice storms, thunderstorms, steady rains from a cold front or warm front, excessive heat, heat waves and more.

Weather can change dramatically from day to day. However, the average weather condition of a place for a longer period of time represents the climate.

Do you know the exact difference between weather and climate? The difference between weather and climate is that weather consists of the short-term (minutes to months) changes in the atmosphere. In most places, weather can change from minute-to-minute, hour-to-hour, day-to-day, and season-to-season.

However, climate is the average weather for a particular region and time period, usually taken over 30-years. An easy way to remember the difference is that climate is what you expect, like a very hot summer, and weather is what you get, like a hot day with pop-up thunderstorms. When scientists talk about climate, they are looking at averages of precipitation, temperature, humidity, sunshine, wind velocity, and phenomena such as fog, frost, hail storms, and other measures of the weather that occur over a long period in a particular place. It is relevant to study about climate and climate changes, as they affect people around the world

Table 1.1.1 The differences between weather and climate

Recap

Objective type questions

Answer to Objective type questions

Self Assessment Questions

Assignment

Suggested Reading

References