Biosphere

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Biosphere

The biosphere is the space on and near Earth’s surface that contains and supports living organisms and ecosystems. The biosphere is, in the broadest sense, the global ecosystem. The biosphere interacts with the lithosphere, atmosphere, and hydrosphere. The lithosphere is the outer surface of Earth composed of solid soil and rock, the atmosphere is the surrounding gaseous envelope, and the hydrosphere refers to Earth’s liquid water including lakes, rivers, and oceans. In order to study the processes associated with the biosphere, a multi-disciplinary effort has been employed by scientists from such fields as chemistry, biology, geology, and ecology.

History

The Austrian geologist Eduard Suess (1831–1914) first used the term biosphere in 1875 to describe the space on Earth that contains life. The concept introduced by Suess had little impact on the scientific community until it was resurrected by the Russian scientist Vladimir Vernadsky (1863–1945) in 1926 in his book, La biosphere. In that work Vernadsky extensively developed the modern concepts that recognize the interplay between geology, chemistry, and biology.

KEY TERMS

Decomposition— The breakdown of the complex molecules composing dead organisms into simple nutrients that can be reutilized by living organisms.

Energy— The ability to do work. Energy occurs in various forms. The most important ones in biospheric processes are solar (electromagnetic), kinetic, heat (or thermal), and chemical-bond energies.

Global warming— Atmospheric warming caused by an increase in the concentration of greenhouse gases, which absorb infrared energy emitted by Earth’s surface, thereby slowing its rate of cooling. Carbon dioxide and water vapor are particularly important in this respect.

Nutrient cycle— The cycling of biologically important elements from one molecular form to another, and eventually back to the original form.

Nutrients— The molecules organisms obtain from their environment and are used for growth, energy, and other metabolic processes.

Photosynthesis— Enzymatic, sunlight-induced reaction between carbon dioxide and water, which produces oxygen and organic molecules. Plants, algae, and certain bacteria are photosynthetic organisms.

Respiration— Enzymatic chemical reactions between organic molecules and oxygen, which result in the production of carbon dioxide, water, and energy.

Requirements for life

In order for organisms to survive, appropriate temperature ranges, moisture conditions, energy supply, and nutrient supply must be present in the environment.

Energy is needed for metabolic functions, including growth, movement, waste removal, and reproduction. In most ecosystems, this energy is supplied from a source outside the biosphere, in the form of electromagnetic energy received from the Sun. This electromagnetic radiation is captured and stored by plants through the process of photosynthesis. Photosynthesis involves a light-induced, enzymatic reaction between carbon dioxide and water, which produces oxygen and glucose, an organic compound. The glucose is used, through an immense diversity of biochemical reactions, to manufacture the huge range of other organic compounds found in organisms. Potential energy is stored in the chemical bonds of organic molecules and can be released through the process of respiration; this involves enzymatic reactions between organic molecules and oxygen to form carbon dioxide, water, and energy. The growth of organisms is achieved by the accumulation of organic matter, also known as biomass. Plants and some microorganisms are the only organisms that can form organic molecules by photosynthesis. Nearly all heterotrophic organisms, including animals, ultimately rely on photosynthetic organisms to supply their energy needs.

The major elements that comprise the chemical building blocks of organisms are carbon, oxygen, nitrogen, phosphorus, sulfur, calcium, and magnesium. Organisms can only acquire these elements if they occur in chemical forms that can be assimilated from the environment; these are termed available nutrients. Nutrients contained in dead organisms and biological wastes are transformed by decomposition into compounds that organisms can reutilize. In addition, organisms can utilize some mineral sources of nutrients. All of the uptake, excretion, and transformation reactions are aspects of nutrient cycling.

The various chemical forms in which carbon occurs can be used to illustrate nutrient cycling. Carbon occurs as the gaseous molecule carbon dioxide, and in the immense diversity of organic compounds that make up living organisms and dead biomass. Gaseous carbon dioxide is transformed to solid organic compounds (simple sugars) by the process of photosynthesis. The process of respiration returns carbon dioxide to the atmosphere at about the same rate that it is consumed.

Evolution of the biosphere

During the long history of life on Earth (about 3.8 billion years), organisms have drastically altered the chemical composition of the biosphere. At the same time, the biosphere’s chemical composition has influenced which life forms could survive. For example, when life first evolved, the atmospheric concentration of carbon dioxide was much greater than today, and there was almost no free oxygen. After the evolution of photosynthesis there was a large decrease in atmospheric carbon dioxide and an increase in oxygen. Much of carbon once present in the atmosphere as carbon dioxide now occurs in fossil fuel deposits and limestone rock.

The increase in atmospheric oxygen concentration had an enormous influence on the evolution of life. It was not until oxygen reached similar concentrations to what occurs today (about 21%, by volume) that heterotrophic multicellular organisms were able to evolve. Such organisms require high oxygen concentrations to accommodate their high rate of respiration.

Current research

Much research investigating the biosphere is aimed at determining the effects of human activities. Pollution, fertilizer application, changes in land use, fuel consumption, and other human activities affect interactions with the hydrosphere, atmosphere and lithosphere and damage functional components of the biosphere. Depletion of the ozone layer that protects organisms from intense exposure to solar ultraviolet radiation and the greenhouse effect that moderates the surface temperature of the planet are two examples of human-induced perterbations to the atmosphere that impact the biosphere. An example of interatctions between the lithosphere, hydrosphere and biosphere are evidenced in the agricultural use of fertilizer, which increases the amounts of nitrogen, phosphorus, and other nutrients in the soil and increases crop yeild. However, excess nutrients in the soil run off into lakes resulting in algal blooms and in some cases massive fish kills.

Recent interest in long-term, manned space operations has spawned research into the development of artificial biospheres. Extended missions in space require that nutrients are cycled in a volume no larger than a building. The Biosphere 2 project, which received a great deal of popular attention in the early 1990s, has provided insight into the difficulty of managing such small, artificial biospheres. Human civilization is also finding that it is difficult to sustainably manage the much larger biosphere of planet Earth.

See also Lithosphere.