The biosphere is defined as the surface and atmosphere of the Earth occupied by living organisms. It extends on land from the deepest root regions of trees to the highest mountain tops, and in the oceans down to the deepest ocean trenches.
The biosphere is about 20 km from top to bottom, but almost all life exists between 300 m below the surface of the oceans to c. 6 km above sea level.
Origin of the biosphere
The biosphere has existed for about 3.5 billion years. The earliest life forms were a type of Prokaryote (microscopic single-celled organisms without a distinct nucleus) called the Archaebacteria that survived in an atmosphere that did not include oxygen. Later Prokaryotes included the true bacteria (Eubacteria).
Some Prokaryotes developed a process of using the energy from sunlight to make simple sugars with the simultaneous production of oxygen – a process called photosynthesis. These photosynthetic microorganisms gradually produced so much oxygen that the characteristics of the atmosphere were changed. More complex life-forms then developed such as multicellular fungi, plants, animals – and humans.
The biosphere as an ecosystem
The biosphere is sometimes regarded as a single entity – a complex community of many types of organisms functioning as s single unit. Alternatively, the biosphere may be regarded as consisting of a number of inter-related smaller ecosystems such as lakes, forests, oceans. Each of these smaller ecosystems consists of differing combinations of an abiotic (non-living) portion (climate, water, energy flow, nutrients, inorganic and organic chemicals), and a biotic (living) portion consisting of microorganisms, plants, animals and humans.
Energy flow in the biosphere
All life on Earth ultimately depends upon three categories of organisms: .
- the microalgae, macroalgae and green plants that use the process of photosynthesis to convert solar energy into chemical energy (primary producers)
- animals and humans (consumers)
- microorganisms that break down the remains of animals and plants into simpler components for recycling through the biosphere (decomposers)
Effect of the biosphere on climate change
The role that human activity – part of the biosphere – is having on climate change is well documented and discussed in several other parts of this site, e.g the effect of greenhouse gases. Land use changes can also have a significant effect on the climate.
This concludes our brief look at how the pre-industrial climate originated and which are the major ecosystems controlling it.
Now we can take a look at the current climate and the phenomenon of climate change itself..