CONCEPT OF BIOSPHERE

The abiotic and biotic components of environment on this planet earth, occupy a limited area that we normally refer to as biosphere. It is the part of earth above and below the surface which supports life. The biosphere (bio-life; a sphere around the earth's surface that supports life) could further be recognized as a combination of Eubiosphere (Eu means true) and parabiosphere (para means subsidiary or auxiliary). The latter i.e. parabiosphere constitutes that part of biosphere which is harsh or not hospitable to life-for example regions of volcanoes, cold ice-cap containing deserts, arid hot deserts, geysers and heavily polluted areas of land and water. The eubiosphere, on the other hand, comprises the remaining regions that support life. It comprises three chief media-air, water and land/ earth. These are thus recognized as:

1. Lithosphere or Pedosphere (Litho-rock, Pedo-soil)

2. Hydrosphere (envelope of water)

3. Atmosphere (envelope of air)

Each of these divisions of the biosphere comprises non-living (abiotic) and living (biotic) components. There exists a strong interaction and influence of the components around themselves and between one another. In other words, the living organisms say a tree serves as food for a leaf eating insect which in turn serves as food for a bird and so on. At the same time that tree is being held in position by the pedosphere and supported by the water (contained in the soil/pedosphere ) and the air of the atmosphere. By transpiring water into the atmosphere it lowers the temperature of the atmosphere and so on. It thus, becomes clear that the biotic and abiotic components of the atmosphere, lithosphere and hydrosphere interact and influence the performance of each component directly and indirectly.

Any external force or a component, substance or a condition that affects the organism in any way is referred to as environmental factor or force. The sum total of all these factors acting on the organism constitutes its environment.

The components of environment are always in a constant phase of inter-relationship and mutual dependence. For instance, wind lowers the temperature or high temperature evaporates the water and increases the relative humidity of the air. Plants due to transpiration make the air humid and lower the temperature. Plants make food for animals and recycle the generation of oxygen. Such inter relationships form an intricate web in the natural environment. For instance the biotic environment, for a squirrel includes the acorns it eats, the blue joys that compete with it for the nuts, the ticks that are parasites and weaken its body, and its relatives (siblings) that share its territory. The abiotic environment includes the rainfall, sunlight and soil that regulate acorn production and the hot and cold temperature that the squirrel must face in summer and winter.

LITHOSPHERE

 The lithosphere or land constitutes the abiotic component of the environment. Comprising 29% of the earth's area the land provides the habitat for plants and animals. Although almost static in terms of geological size the land surface is constantly undergoing changes. These modifications of the surface area and features are the result of both internal forces (also called endogenetic forces) and external forces (also called exogenetic forces). While the former include tectonic forces, continent building forces and mountain building forces; the latter refer to erosion, weathering and depositions which sculpture the earth's surface features.

The lithosphere broadly includes

1. The continents which are the macro-landforms resulting from tectonic forces;

2. The mountains, plateaus and plains or meso landforms resulting from various earth movements/endogenetic forces;

3. The vast variety of landform features such as valleys, beaches, sand-dunes, deltas etc. created by exogenetic forces;

4. The soils or pedosphere which includes a variety of soil types such as alluvial, loam, laterite etc.

5. Rocks such as the sedimentary, igneous and metamorphic; and

6. Minerals and elements such as iron, nickel, carbon, nitrogen, oxygen etc.

A wide variety of geological and geomorphic features on the earth’s surface which are primarily the result of various processes such as tectonic processes, geochemical cycle, water cycle as also uplifting, sinking, glacial action, weathering, erosion etc. are of great significance to man e.g. the landforms determine the area of habitability on earth while the soils provide the supporting capacity of an area. The mineral resources, metallic, non-metallic and petroleum contained in the lithosphere have greatly influenced the extent of industrial development in different parts of the world. At the same time however, the zones of earthquakes and volcanoes present a serious environmental hazard for human existence.

However, it may be emphasized that although the lithosphere as a component of the environment is a repository of a wide variety of resources such as soils and minerals their improper use and over-use by man has led to a situation of grave concern. While technology can be used to get higher yields but nothing can hasten the natural processes to rebuild or compensate loss and damage to these resources.

HYDROSPHERE

The hydrosphere comprises 71% of the earth's surface area. Being essential for all life processes, water is fundamental to existence. The water on earth is contained in oceans, seas, rivers, lakes, ponds, as water vapor in the atmosphere; as ground water and also in ice-caps and glaciers. The hydrosphere plays a vital role in the circulation of nutrients between the different parts of the environment. It also forms the basis of the biogeochemical cycle which involves the taking in of nutrients in solution form from the soil by plants through their roots. The processes that maintain the cyclic flow of water in the environment and link the hydrosphere to the atmosphere and land are known as the hydrological cycle. This cycle involves all the three states of water, liquid, gaseous (water vapor), and solid (as in ice and glaciers). It also includes the transformation processes from one state to another i.e. evaporation (from liquid to gaseous) and condensation (from gas to liquid) as also freezing, melting etc. The main source of energy that keeps the hydrological cycle going comes from the sun.

Evaporation occurs when due to the heat of the sun, water evaporates from water bodies i.e. oceans, seas, lakes, rivers etc. The process by which water evaporates from plant surfaces is known as transpiration. Both evaporation and transpiration cause the presence of water vapor in the atmosphere. In constant horizontal motion as water droplets/ice crystals, the water vapor eventually condenses/freezes to fall on the earth's surface as rain, sleet, hail and snow. This process is known as precipitation.

Water which is derived from precipitation either flows on the land surface as run-off or percolates through the soil to collect in aquifers below the ground as ground water. Run-off refers to surface water as in rivers, streams, ponds, lakes etc.

ATMOSPHERE

The gaseous envelope that surrounds the earth is known as the atmosphere. It is a dynamic system, changing continuously. A complex mixture of gases constitutes the air i.e. the atmosphere. The atmosphere comprises Nitrogen (N2, 78%), Oxygen (02, 20.9%), Argon (Ar, 0.9%), Carbon dioxide (CO2, 0.03%) and variable amounts of other trace elements. With the exception of molecular argon and other noble or inert gases, all the compounds in the earth's atmosphere are produced or removed by biological activity, or are greatly affected by the biota. Although, the atmosphere has been greatly modulated by life during the last 3.5 billion years, most of the changes have been natural and have contributed to producing an atmosphere that is relatively constant and essential to our survival.

The atmosphere has a layered structure and comprises five distinct zones i.e.

1. Troposphere, the layer immediately adjacent to the earth's surface extends upto a distance of 0-9kms. at the poles and 17kmsat the equator. This contains 80% of the total mass of the atmosphere. Water vapors and dust particles are present in this layer and the air is not static but in constant circulation;

2. Stratosphere, extending upto nearly 30 km from the Troposphere is relatively stable in terms of air temperature which may increase with height. Ozone is also concentrated in this layer.

3. Mesosphere, extending upto 50 kms. from the stratosphere and

4. Thermosphere, which occurs at 90 to 500 kms. from the earth’s surface. Temperature changes are abrupt and highly ionized gases occur here. Temperature is very high.

5. Exosphere, is the outer most layer of the earth’s atmosphere. It is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules. The exosphere merges with the emptiness of outer space where there is no atmosphere.

The atmosphere however, serves various functions which are basic to existence of life on earth such as:

1. It gives life-giving gases such as oxygen (O2) for man and animals, and carbon dioxide (CO2) for plants to be used for manufacture of food.

2. It traps infrared radiation and transforms it into thermal motion, hence warming the surface of the earth.

3. It also serves as a store house for water vapors which lead to precipitation/rain.

4. It absorbs cosmic rays which can otherwise ionize everything on the earth.

5. It protects the earth from the unfriendly environment of outer space. Any intruding substances get burnt up in it.

6. It has a radio window for the transmission of waves of 1 to 40 km. (nano meter).

7. It bas a self cleaning ability through rainfall.