Biosphere (Encyclopedia of Environmental Issues, Revised Edition)
The concept of the biosphere was introduced in the nineteenth century by Austrian geologist Eduard Suess. The biosphere is the zone, approximately 20 kilometers (12 miles) thick, that extends from the floors of the earth’s oceans to the tops of the mountains, within which all life on the planet exists. It is thought to be more than 3.5 billion years old, and it supports nearly one dozen biomes, regions of similar climatic conditions within which distinct biotic communities reside.
Compounds of hydrogen, oxygen, carbon, nitrogen, potassium, and sulfur are cycled among the four major spheres—biosphere, lithosphere, hydrosphere, and atmosphere—to make the materials that are essential to the existence of life. The most critical of these compounds is water, and its movement between the spheres is called thewater cycle. Dissolved water in the atmosphere condenses to form clouds, rain, and snow. The annual precipitation for a region is one of the major controlling factors in determining the terrestrial biome that can exist. The water cycle follows the precipitation through various paths leading to the formation of lakes and rivers. These flowing waters interact with the lithosphere to dissolve chemicals as they flow to the oceans, where about one-half of the biomes on earth occur. Evaporation of water from the oceans resupplies the vast majority of the moisture existing in the atmosphere. This cycle supplies water continuously for the needs...
(The entire section is 447 words.)
Desert Biome (Encyclopedia of Environmental Issues, Revised Edition)
The major deserts of the world are located between 20 to 30 degrees latitude north and south of the equator. The annual precipitation in a desert biome is less than 25 centimeters (10 inches) per year. Deserts are located in northern and southwestern Africa, parts of the Middle East and Asia, Australia, the southwestern United States, and northern Mexico.
Deserts are characterized by life that is unique in its ability to capture and conserve water. Deserts show the greatest extreme in temperature fluctuations of all biomes: Daytime temperatures can exceed 49 degrees Celsius (120 degrees Fahrenheit), and night temperatures can drop to 0 degrees Celsius (32 degrees Fahrenheit). Most of the animals that live in desert biomes are active at night and retreat to underground burrows or crevices during the day to escape the heat. The water cycle in deserts rarely provides surface water, so plant life usually finds water through a wide distribution of shallow roots to capture the near-surface infiltration or a deep taproot system that finds groundwater located below the surface of dry streambeds. The plant life is characterized by scattered thorny bushes, shrubs, and occasional cacti. Animal life consists of an abundance of reptiles (mostly lizards and snakes), rodents, birds (many predatory types such as owls and hawks), and a wide variety of insects.
Deserts and semideserts cover approximately one-third of the land surface on...
(The entire section is 237 words.)
Grassland Biome (Encyclopedia of Environmental Issues, Revised Edition)
Grasslands are found in a wide belt of latitudes higher than those in which desert biomes exist. Large grassland regions occur in central North America, central Russia and Siberia, subequatorial Africa and South America, northern India, and Australia. This biome flourishes in moderately dry conditions, having an annual rainfall between 25 and 150 centimeters (10 and 60 inches). Precipitation and solar heating are unevenly divided throughout the year, providing a wet, warm growing season and a cool, dry dormant season.
The animal life in grassland regions is characterized by large grazing mammals, such as wild horses, bison, antelopes, giraffes, zebras, and rhinoceroses, as well as smaller herbivores, such as rabbits, prairie dogs, mongooses, kangaroos, and warthogs. This abundance of herbivores allows for a large development of secondary and tertiary consumers in the food chain, such as lions, leopards, cheetahs, wolves, and coyotes. Grasslands have rich soils that provide the fertile growing conditions for a wide variety of tall and short grasses. Within a single square meter of this healthy soil, several hundred thousand living organisms can be found, from microbes to insects, beetles, and worms. The profusion of these smaller life-forms fosters an abundance of small birds.
Grasslands have been environmentally stressed as humans have converted them to farmland because of their rich soils and to rangeland because of...
(The entire section is 253 words.)
Tropical Rain-Forest Biome (Encyclopedia of Environmental Issues, Revised Edition)
Rain forests receive heavy rainfall almost daily, with an annual average of more than 240 centimeters (95 inches). Temperatures in these areas are fairly constant from day to day and season to season, with an annual mean value of about 28 degrees Celsius (82 degrees Fahrenheit). The combination of plentiful rain and high temperatures causes high humidity, allowing some plants to utilize the atmosphere for their water supply via “air roots.” This biome is also unique because the chemical nutrients needed to sustain life within it are almost entirely contained in the lush vegetation of the biosphere itself and not in the upper layers of soil of the lithosphere. The soils are thin and poor in nutrients.
The tropical rain forests contain a wider diversity of plant and animal species per unit area than any other biome. It is estimated that nearly two-thirds of all the plants and insects found on earth are contained in tropical rain forests. This enormous biodiversity is accommodated in part because each form of plant or animal occupies a specialized niche based on its ability to thrive with a particular level of sunlight that corresponds to a given height above the forest floor within the forest canopy. Numerous exotic insects, amphibians, reptiles, birds, and small mammals can coexist within a single canopy level. The plants growing in tropical rain forests currently provide ingredients found in 25 percent of the...
(The entire section is 338 words.)
Temperate Forest Biome (Encyclopedia of Environmental Issues, Revised Edition)
Temperate forests exist in areas where temperatures change dramatically during the four distinct seasons. Temperatures fall below freezing during the winter, with warmer, more humid conditions during the summer. Rainfall averages between 75 and 200 centimeters (30 and 80 inches) per year. This biome is often divided into forests with broad-leaved deciduous (leaf-shedding) trees and those with coniferous (cone-bearing) trees. Deciduous forests develop in regions with higher precipitation values, whereas the needle-like evergreen leaves of conifers have scales and thick, waxy coatings that allow them to flourish at the lower end of the precipitation range.
Deciduous forests develop more solid canopies with widely branching trees such as elm, oak, maple, ash, beech, and other hardwood varieties. The forest floor often contains an abundance of ferns, shrubs, and mosses. Coniferous forests are usually dominated by pine, spruce, fir, cedar, and hemlock trees. Some deciduous trees, such as aspen and birch, often occur with the conifers. The coniferous forest floor is so acidic from decomposing evergreen needles that often only lichens and mosses can grow.
Temperate forests are home to diverse animal life. Common mammals of deciduous forests include squirrels, chipmunks, porcupines, raccoons, opossums, deer, foxes, black bears, and mice. Snakes, toads, frogs, and salamanders exist alongside a large bird population of...
(The entire section is 271 words.)
Tundra Biome (Encyclopedia of Environmental Issues, Revised Edition)
Tundras occur in areas near the Arctic ice cap and extend southward across the far northern parts of North America, Europe, and Asia. During the majority of the year, these largely treeless plains are covered with ice and snow and are battered by bitterly cold winds. Tundras are covered with thick mats of mosses, lichens, and sedges (grasslike plants). Because the winters are long and dark, tundra vegetation grows during the three months of summer, when there is almost constant sunlight.
Bogs, marshes, and ponds are common on the summer landscape because permafrost, a thick layer of ice that remains beneath the soil all year long, prevents drainage of melted waters. These wet areas provide perfect breeding grounds for mosquitoes, deerflies, and blackflies during the brief summer. These insects in turn serve as a source of food for migrating birds. Larger mammals, such as caribou, reindeer, musk ox, and mountain sheep, migrate in and out of the tundra. Some animals, such as lemmings, arctic hares, grizzly bears, and snowy owls, can be found in the tundra during all times of the year.
The tundra is the earth’s most fragile terrestrial biome. Vegetation disturbed by human activity can take decades to replenish itself. Roads and pipelines must be constructed on bedrock or layers of added gravel; otherwise, they will melt the upper layers of the permafrost.
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Oceanic Biomes (Encyclopedia of Environmental Issues, Revised Edition)
Oceans cover 70 percent of the earth’s surface and contain 97.6 percent of the water of the hydrosphere. They play a primary role in regulating the earth’s distribution of heat, and they are central to the water cycle. Oceans are instrumental in the survival of all life on earth. In addition, oceans house more than 250,000 species of marine plants and animals that occur as six common biomes.
Coral reefs are coastal biomes that develop on continental shelves in regions of clear, tropical waters. Collectively, coastal biomes make up only 10 percent of the world’s ocean area but contain 90 percent of all ocean species. These are the regions where most commercial fishing is done. The vast open oceans contain only 10 percent of all oceanic species. Vegetation is mostly limited to free-floating plankton. Exotic bottom fauna exist on deep hydrothermal vents. Animal life includes whales, dolphins, tuna, sharks, flying fish, and squids.
A number of transitional biomes also exist at the ocean-land interface. The intertidal biome can be composed of sandy beaches or more rocky zones that are covered by water only during periods of high tide. A variety of crustaceans and mollusks are found on wet sandy beaches, whereas rock tidal pools contain kelp, Irish moss, and rockweed, all of which compete for space with snails, barnacles, sea urchins, and starfish.
(The entire section is 220 words.)
Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Butz, Stephen D. Science of Earth Systems. 2d ed. Clifton Park, N.Y.: Thomson Delmar Learning, 2008.
Ehrlich, Paul R., and Anne H. Ehrlich. Extinction: The Causes and Consequences of the Disappearance of Species. New York: Ballantine Books, 1981.
Krebs, Robert E. “Biosphere: Envelope of Life.” In The Basics of Earth Science. Westport, Conn.: Greenwood Press, 2003.
McNeely, Jeffrey A., et al. Conserving the World’s Biological Diversity. Washington, D.C.: Island Press, 1990.
Smil, Vaclav. The Earth’s Biosphere: Evolution, Dynamics, and Change. Cambridge, Mass.: MIT Press, 2002.
Weiner, Jonathan. The Next One Hundred Years. New York: Bantam Books, 1990.
Wilson, E. O., ed. Biodiversity. Washington, D.C.: National Academy Press, 1990.
Woodward, Susan L. Introduction to Biomes. Westport, Conn.: Greenwood Press, 2009.
(The entire section is 116 words.)
Background (Encyclopedia of Global Resources)
The first use of the term “biosphere” dates to 1875, when geologist Eduard Suess described layers of the Earth in his book on the origin of the Alps. The Russian geologist Vladimir Vernadsky popularized the term in his lectures, published in French in 1929 as La Biosphere. Vernadsky noted that the concept, although not the term, had originated much earlier with the French biologist Jean-Baptiste Lamarck (1744-1829).
(The entire section is 65 words.)
Extent of the Biosphere (Encyclopedia of Global Resources)
Although most people would think nothing of traveling 50 kilometers to a nearby town, journeying upward far less than this distance would mean certain death without a special support system. As altitude increases, decreases in pressure, vital gases, and temperature prevent active metabolism. However, dormant bacterial and fungal spores can apparently drift upward indefinitely in this “parabiosphere.” Most jet plane passengers are aware that artificial cabin pressure is required to sustain them in the thinning atmosphere when they are only a few kilometers high. Chlorophyll plants cannot live above about 6,200 meters because all water freezes at that altitude and the carbon dioxide available for photosynthesis is at less than half that available at sea level. The few spiders and springtails that live on top of Mount Everest survive on plant and animal debris blown up there by wind currents.
Life also extends downward into the deepest ocean trenches, although the density of organisms is drastically less in the dark zones beneath the thin top layer, where sunlight feeds algae and the resultant food chains. Most deep-ocean organisms must feed on the rain of organic matter that sinks from the surface or feed in the detritus food chain. Many organisms live on the surface of the ocean bottom, and sampling studies have shown that life extends deep into these bottom muds. Not all organisms here derive their energy...
(The entire section is 299 words.)
Biomes (Encyclopedia of Global Resources)
The terrestrial part of the biosphere can be subdivided into such categories as hot and wet tropical rain forests, frozen arctic tundra, cold mountaintop meadows, and prairie grasslands. These natural communities with similar plants and animals are called “biomes.” For example, conifer forests stretch around the upper latitudes of Canada, Europe, and Russia. Although the species of conifer trees, large grazers, and predators differ, the ecology is very similar. The same is true for the grassland biome that occurs in the U.S. plains states, Russia, Argentina, and South Africa, and the temperate deciduous forests of the eastern United States, Europe, and China. Other biomes include taiga, savanna, thornbush, chaparral, and various tropical rain forest types.
The first breakdown of biotic communities was made by C. Hart Merriam, working in 1890 in California and Arizona; his “vegetative life zones” were based on temperature and ignored rainfall. Victor E. Shelford added detailed descriptions of animal associations but did not try to correlate communities with climate. While Shelford’s followers consider biomes to be distinct entities, other ecologists view them as human concepts that hide the fact that communities gradually blend into one another. The biome concept finds use in the biosphere reserve program, which is based on environmental planning aimed at saving substantial portions of each unique biome.
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Energy Entering the Biosphere (Encyclopedia of Global Resources)
The biosphere concept serves an accounting function by placing all living systems on one enclosed “spaceship Earth”—a concept that became far easier for the public to visualize when the space program provided actual photographs of Earth as a planet. It became obvious that energy input was limited and that nutrients must be recycled. The Earth intercepts about 2.5 billion billion horsepower of energy per year as sunlight. Most reflects back into space or temporarily heats surfaces. Because photosynthetic leaves and algae intercept less than 1 percent of this light, there is a limit on the amount of plant life that can be supported and on the amount of animal life and decomposers that can be fed. Ecologists have estimated that the maximum amount of living tissue (both animals and plants) that can be supported in the biosphere each year is about 370 billion metric tons, consisting of about 260 billion metric tons of plants and 110 billion metric tons of consumers.
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Cycles in the Biosphere (Encyclopedia of Global Resources)
Water in the biosphere is stable at about 1.5 billion cubic kilometers, all but 3 percent of which is salt water in oceans. Three-quarters of fresh water has been estimated to be frozen in glaciers and polar ice caps. The Earth’s water cycle (hydrologic cycle), then, involves less than 1 percent of the total water, which evaporates from ocean surfaces or transpires through plant leaves and then precipitates back down as rain, snow, and so on. While water is involved in the photosynthesis reaction, water is far more important in plant transpiration, where on average a hundred units of water must flow through a plant to produce one unit of plant tissue. More than any other factor, the pace of the water cycle and the uneven distribution of water account for the variation in vegetation zones on the Earth’s land surfaces.
In addition to the hydrogen and oxygen in water, all organisms use carbon, nitrogen, phosphorus, sulfur, sodium, potassium, and many other elements. Whereas water may evaporate and condense back down in an average of ten days, carbon may take a decade to cycle. In the atmosphere, 635 billion metric tons of carbon exist as carbon dioxide. Green plants convert a portion into carbon in plant tissues on land (408 billion metric tons) or in phytoplankton (4.5 billion metric tons) each year. Decomposition returns some carbon in dead organic matter (408 billion metric tons) to the atmosphere as carbon...
(The entire section is 501 words.)
Further Reading (Encyclopedia of Global Resources)
Huggett, Richard John. The Natural History of the Earth: Debating Long-Term Change in the Geosphere and Biosphere. New York: Routledge, 2006.
Lovelock, James. Gaia: A New Look at Life on Earth. New York: Oxford University Press, 2000.
_______. The Vanishing Face of Gaia: A Final Warning. New York: Basic Books, 2009.
Rambler, Mitchell B., Lynn Margulis, and René Fester, eds. Global Ecology: Towards a Science of the Biosphere. Boston: Academic Press, 1989.
Samson, Paul R., and David Pitt, eds. The Biosphere and Noosphere Reader: Global Environment, Society, and Change. New York: Routledge, 1999.
Smil, Vaclav. The Earth’s Biosphere: Evolution, Dynamics, and Change. Cambridge, Mass.: MIT Press, 2002.
Trudgill, Stephen. The Terrestrial Biosphere: Environmental Change, Ecosystem Science, Attitudes, and Values. New York: Prentice Hall, 2001.
(The entire section is 117 words.)
Biosphere (Encyclopedia of Science)
The biosphere is the space on or near Earth's surface that contains and supports living organisms. It is subdivided into the lithosphere, atmosphere, and hydrosphere. The lithosphere is Earth's surrounding layer, composed of solids such as soil and rock; it is about 80 to 100 kilometers (50 to 60 miles) thick. The atmosphere is the surrounding thin layer of gas. The hydrosphere refers to liquid environments such as lakes and oceans that lie between the lithosphere and atmosphere. The biosphere's creation and continuous existence results from chemical, biological, and physical processes.
Requirements for life
For organisms to live, certain environmental conditions (such as proper temperature and moisture) must exist, and the organisms must be supplied with energy and nutrients (food). All the animal and mineral nutrients necessary for life are contained within Earth's biosphere. Nutrients contained in dead organisms or waste products of living cells are transformed back into compounds that other organisms can reuse as food. This recycling of nutrients is necessary because there is no source of food outside the biosphere.
(The entire section is 1450 words.)
Biosphere (World of Earth Science)
The biosphere is the space on and near Earth's surface that contains and supports living organisms and ecosystems. It is typically subdivided into the lithosphere, atmosphere, and hydrosphere. The lithosphere is the earth's surrounding layer composed of solid soil and rock, the atmosphere is the surrounding gaseous envelope, and the hydrosphere refers to liquid environments such as lakes and oceans, occurring between the lithosphere and atmosphere. The biosphere's creation and continuous evolution result from physical, chemical, and biological processes. To study these processes a multi-disciplinary effort has been employed by scientists from such fields as chemistry, biology, geology, and ecology.
The Austrian geologist Eduard Suess (1831914) 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 (1863945) 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 in biospheric processes.
For organisms to live, appropriate environmental conditions must exist in terms of temperature, moisture, energy supply, and nutrient availability.
Energy is needed to drive the functions that organisms perform, such as growth, movement, waste removal, and reproduction. Ultimately, this energy is supplied from a source outside the biosphere, in the form of visible radiation 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. Heterotrophic organisms, including humans, 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, as mentioned previously. As organisms grow they deplete the atmosphere of carbon dioxide. If this were to continue without carbon dioxide being replenished at the same rate as the consumption, the atmosphere would eventually be depleted of this crucial nutrient. However, carbon dioxide is returned to the atmosphere at about the same rate that it is consumed, as organisms respire their organic molecules, and microorganisms decompose dead biomass, or when wildfire occurs.
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 inhabit its environments. Rates of nutrient transformation have not always been in balance, resulting in changes in the chemical composition of the biosphere. 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 multicellular organisms were able to evolve. Such organisms require high oxygen concentrations to accommodate their high rate of respiration.
Most research investigating the biosphere is aimed at determining the effects that human activities are having on its environments and ecosystems. Pollution, fertilizer application, changes in land use, fuel consumption, and other human activities affect nutrient cycles and damage functional components of the biosphere, such as 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.
For example, fertilizer application increases the amounts of nitrogen, phosphorus, and other nutrients that organisms can use for growth. An excess nutrient availability can damage lakes through algal blooms and fish kills. Fuel consumption and land clearing increases the concentration of carbon dioxide in the atmosphere, and may cause global warming by intensifying the planet's greenhouse effect.
Recent interest in long-term, manned space operations has spawned research into the development of artificial biospheres. Extended missions in space require that nutrients be 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 challenging to sustainably manage the much larger biosphere of planet Earth.
See also Atmospheric pollution; Earth (planet); Environmental pollution; Evolution, evidence of; Evolution, mechanisms of; Foliation and exfoliation; Forests and deforestation; Fossil record; Fossils and fossilization; Freshwater; Gaia hypothesis; Solar energy