All plants and animals, including man, share the same ultimate living space. This living space is the ‘biosphere.’ The biosphere is an abstract space made up from parts of the three great earthly spheres, the lithosphere, the hydrosphere and atmosphere.
Man spends the greatest part of his existence on the very surface of the lithosphere-the so called crust. The crust forms only 0.4 per cent of the mass of our planet yet it assumes significances out of all proportion to mass. The crust is important in that it weathers to form the soil, a key physical resource necessary for life.
Also, in the case of mankind, the lithosphere provides a wide range of ‘resources’ in the form of building materials, metalliferous and non-metalliferous ores and fossil fuels.
The lithosphere also provides a surface upon and within which plants and animals can construct their homes, move about on (animals only), and fulfill their life cycle. Without a productive lithosphere it would have been impossible for our civilizations to have developed.
Resting upon the lithosphere and covering it to the extent of some 66 percent is the fluid hydrosphere. Most of the hydrosphere, some 97 percent, has a substantial amount of mineral salts dissolved within it.
These minerals originate in the lithosphere. Only lO^1 percent of the hydrosphere comprises fresh water (devoid of salts), 2 percent of the water is locked up as solid water (ice and snow) and 10~3 percent of the hydrosphere is temporarily located in the atmosphere. The significance of water in our biosphere is of absolute importance; water molecules (HzO) are an essential component of life on planet earth.
The presence of water has allowed the formation of an atmosphere; it permits weathering processes to act upon the lithosphere and it supports all organic life forms.
Most of the waters of our planet are located in the oceans (97 percent). In terms of potential living space, the oceans provide over 2000 times the space provided by the land surface. Unfortunately, only the uppermost one to three meters of the hydrosphere is directly usable by life forms. Below three metres a lack of light and an increase in pressure combine to provide unsuitable living conditions for all but the most specialised creatures. The great volume of the oceans represents a very useful depository for a whole range of man-made pollutants. The use of the hydrosphere as a dumping ground has may unresolve implications for biosphere conservation.
The final component of the biosphere is the gaseous atmosphere, Table. The atmosphere extends for about 32 km but only 5.5 km of this is directly usable by organisms. Beyond 32 km the atmosphere gives way to ‘space’.
The atmosphere provides essential gases necessary for respiration of animals (oxygen) and plants (carbon dioxide). As for the hydrosphere the atmosphere supplies very little by way of directly usable resources for man but its prime use is again a ‘sink’ area for airborne pollutants, both gaseous and particulate in nature.