Biosphere: A Giant Ecosystem

Biosphere: A Giant Ecosystem

What is Biosphere?

• Biosphere is a combination of two Greek words ' Hos (= life) and sphaira (= sphere). Biosphere literally means the sphere where life exists. It is the sphere of action between an organism and its environment. Thus, that part of the earth in which living organism are known to exist, comprising the common part of lithosphere, hydrosphere and atmosphere is called Biosphere.
• The biosphere are mostly found in the relatively narrow zones of contact among the lithosphere (exactly, a fraction of crust), hydrosphere (exactly, a limited part of hydrosphere) and atmosphere (exactly, the lower region—troposphere—of atmosphere).

Extension of Biosphere

• The biosphere extends to any place where life of any kind exist.
• According to Irish biogeographer I oyTivy (1924-95), the 'Organic world' or biosphere is that part of earth which containing living organism—the biological inhabited soil (land), air and water.
• The average thickness of the biosphere or life supporting layer of the earth consisting of land (soil), water and air is approximately 30 km (- up to 9 km deep in the water + 9 km over the land surface + up to 12 km above in the air roughly).
• Most living organisms actually live within a small area in the biosphere, from 500 metres below the surface of the ocean to 6,000 metres above the sea level.
• The biosphere is absent at extremes of the North & South pole, at the highest mountains and in the deepest oceans, because of existing hostile conditions that do not support life. Occasionally spores of bacteria and fungi do found at great height beyond 8,000 metres, but they are not metabolically active, so they represent dormant life only.

Upper limit (in air)

• The upper limit of the biosphere is determined by availability of oxygen, moisture, temperature and air pressure with increase in height in the atmosphere limits the upper boundary of the biosphere.
• Though NASA has detected the presence of bacteria up to the height of 15 km in the atmosphere, but the lower layer of atmosphere up to a few thousand meters accounts the most of the living organisms because favourable enviomment conditions are available for the growth and development of living organism in the lower part of the atmosphere.

Lower Limit:

(a) Over land: The lower limit of biosphere is determined by the availability of required amount of oxygen and light which can sustain life. Thus, the depth of the biosphere over the land is depth of the deepest roots of the trees or depth up to which can live the burrowing organism or the depth at which lie the parent bed-rocks.

(b) In water: The existence of life has been detected up to a depth of 9 km in the deep oceanic trenches and deep sea plants.

Diagramatic Representation of Biosphere

• Diagramatic representation of biosphere is given below —

• From above-mentioned diagram, it is very clear that biosphere is not a separate or fourth sphere of the earth as many think, but it is the common part of the lithosphere, hydrosphere and atmosphere where life exists.
• Our earth is an unique planet in having a biosphere. Biosphere is a life supporting layer which surrounds the earth and makes life of organism possible without any protective device.
• There are a variety of organism in the biosphere. They are broadly divided into the plants, animals and microbes More than 3 lacs plant species and 10 lacs animal species known to exist.
• These organism exist in the zones of contact among lithosphere, hydrosphere and atmosphere. There is exchange of matter and energy among these three constituents of physical environments and the organisms in the biosphere.

Importance of Biosphere

• Though the biosphere is a relatively thin layer of the earth, but it has great significance to our life.
• The biosphere provide a variety of food and also raw materials which provide clothing and shelter and other needs of man.
• Therefore, it is necessary to understand the relationship of organism to one another and to their physical environment.
• Plants, animals and other organism together with the physical environment with which they interact constitute the Ecological system, in short, Ecosystem.
• The term ecosystem was coined by English botanist Arthur Tanslay in 1935.​​​​​​​

The Sun: Driving Force of Ecosystem

• The Sun is the primary sustainer of life on the Earth. Energy from the sun flows through materials and living organism and eventually goes back into space as in the form of heat. Only a tiny part of the Sun's energy falls on earth, but that is enough to keep ecosystem going.
• The Sun is the driving force of an ecosystem. The Sun is the main source of energy which causes changes in the environment. We are very familiar with the day to day changes in weather and seasonal changes in climate. These changes are the result of differences brought in the heating of the earth and its atmosphere by the Sun. Similarly other enviromental changes occured by the solar energy. A field of wheat, a herd of cattle, a crowd of people and a shoal of fish represent example of solar energy stored in various forms.