The biosphere comprises a three dimensional zone extending down into the hydrosphere about 3 m, into the lithosphere for about 2 m and extending upwards into the atmosphere for some 5500 m. Within these orbits, conditions become uniquely suitable for the sustenance of organic life forms.

Although it is possible to study the components of the biosphere in isolation is should be stressed that in reality those parts of the lithosphere, hydrosphere and atmosphere which form the biosphere become intimately interlinked.

Thus the lithosphere has some water and air contained within it, the atmosphere contains water vapour and fine mineral particulate matter while the hydrosphere contains dissolved oxygen and carbon dioxide and suspended mineral matter.

Biosphere and Habitats

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Within the biosphere can be found some distinct ‘habitats’ each comprising specific combinations of energy inputs, moisture availability and nutrients.

Each habitat can be likened to a three dimensional space. The shape comprises a two-dimensional area (length and breadth) which extends either/both upwards into the atmosphere and down into the lithosphere and/ or hydrosphere. Finally, this three dimensional shape evolves and changes its volume with the passage of time.

It is a feature of our biosphere that there are few totally inhospitable conditions for life. Certainly, the hot and cold deserts, the ice-covered polar areas and ocean deeps are the most difficult for life forms to colonise but if a species can become hyper-specialised for survival in a very difficult region then its specialism can become an advantage and isolate it from competition from other species. Having argued for the advantages of specialisation, however, it must be emphasised that the most successful species are the ‘generalists’-species with tolerance of a wide range of different conditions.