Life on our planet earth depends upon a large number of things and services provided by the nature, which are known as natural resources. Water, air, soil, minerals, coal, forests, crops and wild life are all the examples of natural resources.
The basic ecological variables- energy, space, time and diversity are sometimes combined called natural resources. These natural are maintaining ecological balance among themselves. Man is the only organisms who have disrupted this duplicate balance.
According to Ramade (1984), a natural resource is defined as a form of energy and/or matter, which is essential for the functioning of organisms, populations and ecosystems. In the case of humans, a natural resource, in his words, refers to any form of energy or matter essential for the fulfillment of physiological, socio-economic and cultural needs, both at the individual level and that of the community.
The basic ecological variables- energy, space, time and diversity are sometimes combined called natural resources. These natural resources are maintaining ecological balance among themselves. Man is the only organism who has disrupted this duplicate balance.
Classification of natural resources:
According to Odum (1971), natural resources can be divided into two categories such as (1) renewable and (2) Non renewable resources.
1. Renewable resources: The resources that can be replenished through rapid natural cycles are known as renewable resource. These resources are able to increase their abundance through reproduction and utilization of simple substances. Examples of renewable resources are plants, (crops and forests), and animals who are being replaced from time to time because they have the power of reproducing and maintain life cycles. Some examples of renewable resources though they do not have life cycle but can be recycled are wood and wood-products, pulp products, natural rubber, fibers (e.g. cotton, jute, animal wool, silk and synthetic fibers) and leather. In addition to these resources, water and soil are also classified as renewable resources.
Solar energy although having a finite life, as a special case, is considered as a renewable resource in as much as solar stocks are inexhaustible on the human scale.
2. Non-Renewable Resources: The resources that cannot be replenished through natural processes are known as non-renewable resources. These are available in limited amounts, which cannot be increased. These resources include fossil fuels (petrol, coal etc.), metals (iron, copper, gold, silver, lead, zinc etc.), minerals and salts (carbonates, phosphates, nitrates etc.). Once a non-renewable resource is consumed, it is gone forever. Then we have to find a substitute for it or do without it.
Non-renewable resources can further be divided into two categories, viz. a) re-cycle able and b) non-recyclable
a) Recycleale: These are non-renewable resources, which can be collected after they are used and can be recycled. These are mainly the non-energy mineral resources, which occur in the earth's crust (e.g. ores of aluminium, copper, mercury etc.) and deposits of fertilizer nutrients (e.g. phosphate sock and potassium and minerals used in their natural state (asbestos, clay, mica etc.)
b) Non-recyclable: These are non-renewable resources, which cannot be recycled in any way. Examples of these are fossil fuels and uranium, which provide 90 per cent of our energy requirements.
Some authors prefer to classify resources into biotic and abiotic resources:
a) Biotic resources: These are living resources (e.g. forest, agriculture, fish and wild life) that are able to reproduce or replace them and to increase.
b) Abiotic resources: These are non-living resources (e.g. petrol, land, minerals etc.) that are not able to replace themselves or do so at such a slow rate that they are not useful to consider them in terms of the human life times.
Natural resources can be classified as a) inexhaustible and b) exhaustible resources.
1. Inexhaustible resources: The resources which are not changed or exhausted by man's activities and are abundantly available for ever are said to be inexhaustible. Examples are solar energy, atomic energy, wind power, power from tides etc. Most of the renewable resources are classified as inexhaustible. But if not maintained properly, they become extinct. For example, ground water is renewable only if water continues to percolate in the soil at a rate at which it is removed.
2. Exhaustible resources: These resources are limited in nature and they are non-maintainable e.g. coal, petrol and some minerals etc. Hence, they come under non-renewable category.