Earth is composed of
• the atmosphere , enveloping later of air;
• the hydrosphere, parts composed of water; and
• the lithosphere, the solid part.
The biosphere includes the parts of the atmosphere, hydrosphere and lithosphere where life can be found. It is the largest and highest level of biological organization and is composed of various ecosystems.
Boundaries of the biosphere
Compare to the size of earth (Diameter 12,770km) , the biosphere is only a narrow zone about 22km thick, extending from the upper parts of the atmosphere to the depths of the oceans.
The largest number of living organisms is found in the hydrosphere, I.e. the oceans, seas, lakes, ponds , rivers and streams. Most of these aquatic organisms are found near the surface waters where sunlight penetrate to provide energy for aquatic plants to carry out photosynthesis. A few , however, live in the dark depths of the oceans, freezing on the dead organisms and wastes that fall from the surface waters.
The next largest group of organisms is found in the lithosphere, mainly on the land surface. A few terrestrial organisms also lice in the soil, a few meters below the land surface.
In the atmosphere, most living organisms are found up to a height of 7km. Very light pollen grains and spores, however, have been collected at heights above 62km In the atmosphere.
