Biosphere
The biosphere is the largest possible earthly organismic community. It is a terrestrial envelope of life, or the total global biomass of living matter. The biosphere incorporates every individual organism and species on the face of the earth—those that walk on the ground or live in the crevices of rock and down into the soil, those that swim in rivers, lakes, and oceans, and those that move in and out of the atmosphere.
Bios is the Greek word for life; "sphere" is from the Latin sphaera, which means essentially the "circuit or range of action, knowledge or influence," the "place or scene of action or existence," the "natural, normal or proper place." Combined into biosphere, the two ideas define the normal global place of existence for all earthly life-forms and, increasingly, a global area of influence and action for humans. Thinking of the mass of life forms on the earth as the biosphere also provides an impression of circular, cyclic systems and suggests a holistic concept of integration and unity.
A Scientific American book on the biosphere described it as "this thin film of air and water and soil and life no deeper than ten miles, or one four-hundredth of the earth's radius [that] is now the setting of the uncertain history of man." G. E. Hutchinson in that same book asked, "What is it that is so special about the biosphere?" He suggested that the answer seems to have three parts: "First, it is a region in which liquid water can exist in substantial quantities. Second, it receives an ample supply of energy from an external source, ultimately from the sun. And third, within it there are interfaces between the liquid, the solid and the gaseous states of matter." Both of these might better describe what LaMont Cole labeled the "ecosphere," the global eco system—the biosphere plus its abiotic environment. But the significance of Hutchinson's three-part statement is that those three characteristics of the earth's surface make it possible for life to exist. They provide the conditions necessary for the abundant and diverse organisms of the biosphere to live.
Life began in a very different environment than found today: the atmosphere, for example, was mostly methane, ammonia, and carbon dioxide. As life evolved, it changed the atmosphere (and other abiotic components of the surface of the earth), transforming it into the present oxygen-rich mixture of gases vital to life as it now exists. And those life-forms maintain that critical mixture in a complex, fluctuating system of global cycles.
The diversity and complexity of the biosphere is staggering. The accumulated human knowledge of its workings is prodigious, but even more impressive is the immense ignorance of that complexity. Humans have identified about 1.5 million living members of the biosphere and thus have some knowledge of at least that many. However, conservative estimates of the actual number of species begin at 3 or 3.5–5 million species. Recent and less conservative estimates range up to a possible 100 million. That means humans are totally ignorant of anywhere from 50% to as much as 98.5% of the other members of the earth's biological community. Their existence is suspected, but they cannot be identified or their existence documented by even a name.
One of the concerns about large-scale human ignorance of the biosphere is that many species might be extinguished before they are even known. Human activities, especially destruction of habitat, are increasing the normal rate of species extinction. The diversity of the biosphere may be diminishing rapidly.
Taxonomically, the biosphere is organized into five kingdoms: monera, protista, fungi, animalia, and plantae, and a multitude of subsets of these, including the multiple millions of species mentioned above. G. Piel estimates that of the 1,200–1,800 billion tons dry weight of the biosphere, most of it—some 99%—is plant material. All the life-forms in the other four taxons, including animals and obviously the five billion-plus humans alive today, are part of that less than one%.
The biosphere can also be subdivided into biomes: a biome incorporates a set of biotic communities within a particular region exposed to similar climatic conditions and which have dominant species with similar life cycles, adaptations, and structures. Deserts, grasslands, temperate deciduous forests, coniferous forests, tundra, tropical rain forests, tropical seasonal forests, freshwater biomes, estuaries, wetlands, and marine biomes, are examples of specific terrestrial or aquatic biomes.
Another indication of the complexity of the biosphere is a measure of the processes that take place within it, especially the essential processes of photosynthesis and respiration. The sheer size of the biosphere is indicated by the amount of biomass present. Vitousek and his colleagues estimate the net primary production of the earth's biosphere as 224.5 petagrams, one petagram being equivalent to 1015 grams.
The biosphere interacts in constant, intricate ways with other global systems: the atmosphere, lithosphere, hydrosphere, and pedosphere. Maintenance of life in the biosphere depends on this complex network of biological-biological, physical-physical, and biological-physical interactions. All the interactions are mediated by an equally complex system of positive and negative feedbacks—and the total makes up the dynamics of the whole system. Since each and all interpenetrate and react on each other constantly, outlining a global ecology is a major challenge.
Normally biospheric dynamics are in a rough balance. The carbon cycle, for example, is usually balanced between production and decomposition, the familiar equation of photosynthesis and respiration. As Piel notes: "The two planetary cycles of photosynthesis and aerobic metabolism in the biomass not only secure renewal of the biomass but also secure the steady-state mixture of gases in the atmosphere. Thereby, these life processes mediate the inflow and outflow of solar energy through the system; they screen out lethal radiation, and they keep the temperature of the planet in the narrow range compatible with life." But human activities, especially the combustion of fossil fuels, contribute to increases in carbon dioxide, distorting the balance and in the process changing other global relationships such as the nature of incoming and out-going radiation and differentials in temperature between poles and tropics.
If humans are to better understand the biosphere, many more studies must be undertaken on many levels. A number of levels of biological integration must be recognized and analyzed, each with different properties and each offering scholars special problems and special insights. The totality of the biosphere can be broken down in many different ways, but life extends from the single cell to the totality of the globe. Though biologists usually define their disciplines within the bounds of one level and though they may study only one level, scholars should recognize context, the full range of levels and the interactions between them.
Humans are, of course, one of the species that make up the living biosphere. Homo sapiens fits into the Linnean hierarchy on the primate branch. Using that hierarchy as a connective device, humans may take a first step toward understanding how they relate to the rest of the inhabitants of the biosphere, down to the most remote known species.
Humans are without doubt the dominant species in the biosphere. The transformation of radiant energy into useable biological energy is increasingly being diverted by humans to their own use. A common estimate is that humans are now diverting huge amounts of the net primary production of the globe to their own use: perhaps 40% of terrestrial production and close to 25% of all production is either utilized or wasted through human activity. Net primary production is defined as the amount of energy left after subtracting the respiration of primary producers, or plants, from the total amount of energy. It is the total amount of "food" available from the process of photosynthesis—the amount of biomass available to feed organisms, such as humans, that do not acquire food through photosynthesis.
Humans are displacing their neighbors in the biosphere through a multitude of activities: conversion of natural systems to agriculture, direct consumption of plants, consumption of plants by livestock, harvesting and conversion of forests, desertification, and many, many others. The biosphere is the source of all good: humans are an integral part of the biosphere and depend on its functioning for their well-being, for their very lives.
Resources
Books
Bradbury, I. K. The Biosphere. London/New York: Belhaven Press, 1991.
Clark, W. C., and R. E. Munn, eds. Sustainable Development of the Biosphere. Cambridge: Cambridge University Press, 1986.
Piel, G. "The Biosphere." In Only One World: Our Own to Make and to Keep. New York: W. H. Freeman, 1992.
Periodicals
Salthe, S. N. "The Evolution of the Biosphere: Towards a New Mythology." World Futures 30 (1990): 53–67.
Vitousek, P. M., et al. "Human Appropriation of the Products of Photosynthesis." BioScience 36 (1986): 368–373.
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