Environment, the complex of physical, chemical, and biotic factors that act upon an organism or an ecological community and ultimately determine its form and survival.
The Earth’s environment is treated in a number of articles. The major components of the physical environment are discussed in the articles atmosphere, climate, continental landform, hydrosphere, and ocean. The relationship between the principal systems and components of the environment, and the major ecosystems of the Earth are treated in the article biosphere. The significant environmental changes that have occurred during Earth’s history are surveyed in the article geochronology. The pollution of the environment and the conservation of its natural resources are treated in the article conservation. Hazards to life in the biosphere are discussed in the articles death, disease, and immune system.
Historical background
Ecology had no firm beginnings. It evolved from the natural history of the ancient Greeks, particularly Theophrastus, a friend and associate of Aristotle. Theophrastus first described the interrelationships between organisms and between organisms and their nonliving environment. Later foundations for modern ecology were laid in the early work of plant and animal physiologists.
In the early and mid-1900s two groups of botanists, one in Europe and the other in the United States, studied plant communities from two different points of view. The European botanists concerned themselves with the study of the composition, structure, and distribution of plant communities. The American botanists studied the development of plant communities, or succession (see community ecology: Ecological succession). Both plant and animal ecology developed separately until American biologists emphasized the interrelation of both plant and animal communities as a biotic whole.
During the same period, interest in population dynamics developed. The study of population dynamics received special impetus in the early 19th century, after the English economist Thomas Malthus called attention to the conflict between expanding populations and the capability of Earth to supply food. In the 1920s the American zoologist Raymond Pearl, the American chemist and statistician Alfred J. Lotka, and the Italian mathematician Vito Volterra developed mathematical foundations for the study of populations, and these studies led to experiments on the interaction of predators and prey, competitive relationships between species, and the regulation of populations. Investigations of the influence of behaviour on populations were stimulated by the recognition in 1920 of territoriality in nesting birds. Concepts of instinctive and aggressive behaviour were developed by the Austrian zoologist Konrad Lorenz and the Dutch-born British zoologist Nikolaas Tinbergen, and the role of social behaviour in the regulation of populations was explored by the British zoologist Vero Wynne-Edwards. (See population ecology.)
While some ecologists were studying the dynamics of communities and populations, others were concerned with energy budgets. In 1920 August Thienemann, a German freshwater biologist, introduced the concept of trophic, or feeding, levels (see trophic level), by which the energy of food is transferred through a series of organisms, from green plants (the producers) up to several levels of animals (the consumers). An English animal ecologist, Charles Elton (1927), further developed this approach with the concept of ecological niches and pyramids of numbers. In the 1930s, American freshwater biologists Edward Birge and Chancey Juday, in measuring the energy budgets of lakes, developed the idea of primary productivity, the rate at which food energy is generated, or fixed, by photosynthesis. In 1942 Raymond L. Lindeman of the United States developed the trophic-dynamic concept of ecology, which details the flow of energy through the ecosystem. Quantified field studies of energy flow through ecosystems were further developed by the brothers Eugene Odum and Howard Odum of the United States; similar early work on the cycling of nutrients was done by J.D. Ovington of England and Australia. (See community ecology: Trophic pyramids and the flow of energy; biosphere: The flow of energy and nutrient cycling.)
The study of both energy flow and nutrient cycling was stimulated by the development of new materials and techniques—radioisotope tracers, microcalorimetry, computer science, and applied mathematics—that enabled ecologists to label, track, and measure the movement of particular nutrients and energy through ecosystems. These modern methods (see below Methods in ecology) encouraged a new stage in the development of ecology—systems ecology, which is concerned with the structure and function of ecosystems.
Composition
Earth science generally recognizes four spheres, the lithosphere, the hydrosphere, the atmosphere and the biosphere[3] as correspondent to rocks, water, air and life respectively. Some scientists include as part of the spheres of the Earth, the cryosphere (corresponding to ice) as a distinct portion of the hydrosphere, as well as the pedosphere (to soil) as an active and intermixed sphere. Earth science (also known as geoscience, the geographical sciences or the Earth Sciences), is an all-embracing term for the sciences related to the planet Earth.[4] There are four major disciplines in earth sciences, namely geography, geology, geophysics and geodesy. These major disciplines use physics, chemistry, biology, chronology and mathematics to build a qualitative and quantitative understanding of the principal areas or spheres of Earth.
Atmosphere, climate and weather
The atmosphere of the Earth serves as a key factor in sustaining the planetary ecosystem. The thin layer of gases that envelops the Earth is held in place by the planet's gravity. Dry air consists of 78% nitrogen, 21% oxygen, 1% argon, inert gases and carbon dioxide. The remaining gases are often referred to as trace gases.
The atmosphere includes greenhouse gases such as carbon dioxide, methane, nitrous oxide and ozone. Filtered air includes trace amounts of many other chemical compounds. Air also contains a variable amount of water vapor and suspensions of water droplets and ice crystals seen as clouds. Many natural substances may be present in tiny amounts in an unfiltered air sample, including dust, pollen and spores, sea spray, volcanic ash and meteoroids. Various industrial pollutants also may be present, such as chlorine (elementary or in compounds), fluorine compounds, elemental mercury, and sulphur compounds such as sulphur dioxide (SO2).
The ozone layer of the Earth's atmosphere plays an important role in reducing the amount of ultraviolet (UV) radiation that reaches the surface. As DNA is readily damaged by UV light, this serves to protect life at the surface. The atmosphere also retains heat during the night, thereby reducing the daily temperature extremes.
Methods in ecology
Because ecologists work with living systems possessing numerous variables, the scientific techniques used by physicists, chemists, mathematicians, and engineers require modification for use in ecology. Moreover, the techniques are not as easily applied in ecology, nor are the results as precise as those obtained in other sciences. It is relatively simple, for example, for a physicist to measure gain and loss of heat from metals or other inanimate objects, which possess certain constants of conductivity, expansion, surface features, and the like. To determine the heat exchange between an animal and its environment, however, a physiological ecologist is confronted with an array of almost unquantifiable variables and with the formidable task of gathering the numerous data and analyzing them. Ecological measurements may never be as precise or subject to the same ease of analysis as measurements in physics, chemistry, or certain quantifiable areas of biology.
In spite of these problems, various aspects of the environment can be determined by physical and chemical means, ranging from simple chemical identifications and physical measurements to the use of sophisticated mechanical apparatus. The development of biostatistics (statistics applied to the analysis of biological data), the elaboration of proper experimental design, and improved sampling methods now permit a quantified statistical approach to the study of ecology. Because of the extreme difficulties of controlling environmental variables in the field, studies involving the use of experimental design are largely confined to the laboratory and to controlled field experiments designed to test the effects of only one variable or several variables. The use of statistical procedures and computer models based on data obtained from the field provide insights into population interactions and ecosystem functions. Mathematical programming models are becoming increasingly important in applied ecology, especially in the management of natural resources and agricultural problems having an ecological basis.
Controlled environmental chambers enable experimenters to maintain plants and animals under known conditions of light, temperature, humidity, and day length so that the effects of each variable (or combination of variables) on the organism can be studied. Biotelemetry and other electronic tracking equipment, which allow the movements and behaviour of free-ranging organisms to be followed remotely, can provide rapid sampling of populations. Radioisotopes are used for tracing the pathways of nutrients through ecosystems, for determining the time and extent of transfer of energy and nutrients through the different components of the ecosystem, and for the determination of food chains. The use of laboratory microcosms—aquatic and soil micro-ecosystems, consisting of biotic and nonbiotic material from natural ecosystems, held under conditions similar to those found in the field—are useful in determining rates of nutrient cycling, ecosystem development, and other functional aspects of ecosystems. Microcosms enable the ecologist to duplicate experiments and to perform experimental manipulation on them.
Layer of the atmosphere
Principal layers
Earth's atmosphere can be divided into five main layers. These layers are mainly determined by whether temperature increases or decreases with altitude. From highest to lowest, these layers
Exosphere: The outermost layer of Earth's atmosphere extends from the exobase upward, mainly composed of hydrogen and helium.
Thermosphere: The top of the thermosphere is the bottom of the exosphere, called the exobase. Its height varies with solar activity and ranges from about 350–800 km (220–500 mi; 1,150,000–2,620,000 ft). The International Space Station orbits in this layer, between 320 and 380 km (200 and 240 mi). In another way, the thermosphere is Earth's second highest atmospheric layer, extending from approximately 260,000 feet at the mesopause to the thermopause at altitudes ranging from 1,600,000 to 3,300,000 feet.
Mesosphere: The mesosphere extends from the stratopause to 80–85 km (50–53 mi; 262,000–279,000 ft). It is the layer where most meteors burn up upon entering the atmosphere.
Stratosphere: The stratosphere extends from the tropopause to about 51 km (32 mi; 167,000 ft). The stratopause, which is the boundary between the stratosphere and mesosphere, typically is at 50 to 55 km (31 to 34 mi; 164,000 to 180,000 ft).
Troposphere: The troposphere begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (56,000 ft) at the equator, with some variation due to weather. The troposphere is mostly heated by transfer of energy from the surface, so on average the lowest part of the troposphere is warmest and temperature decreases with altitude. The tropopause is the boundary between the troposphere and stratosphere.
Challenges
It is the common understanding of natural environment that underlies environmentalism — a broad political, social and philosophical movement that advocates various actions and policies in the interest of protecting what nature remains in the natural environment, or restoring or expanding the role of nature in this environment. While true wilderness is increasingly rare, wild nature (e.g., unmanaged forests, uncultivated grasslands, wildlife, wildflowers) can be found in many locations previously inhabited by humans.
Goals for the benefit of people and natural systems, commonly expressed by environmental scientists and environmentalists include:
Elimination of pollution and toxicants in air, water, soil, buildings, manufactured goods, and food.
Preservation of biodiversity and protection of endangered species.
Conservation and sustainable use of resources such as water, land, air, energy, raw materials, and natural resources.
Halting human-induced global warming, which represents pollution, a threat to biodiversity, and a threat to human populations.
Shifting from fossil fuels to renewable energy in electricity, heating and cooling, and transportation, which addresses pollution, global warming, and sustainability. This may include public transportation and distributed generation, which have benefits for traffic congestion and electric reliability.
Shifting from meat-intensive diets to largely plant-based diets in order to help mitigate biodiversity loss and climate change.
Establishment of nature reserves for recreational purposes and ecosystem preservation.
Sustainable and less polluting waste management including waste reduction (or even zero waste), reuse, recycling, composting, waste-to-energy, and anaerobic digestion of sewage sludge.
Reducing profligate consumption and clamping down on illegal fishing and logging
Slowing and stabilisation of human population growth.
Reducing the import of second hand electronic appliances from developed countries to developing countries.
Criticism
In some cultures the term environment is meaningless because there is no separation between people and what they view as the natural world, or their surroundings.[48] Specifically in the United States and Arabian countries many native cultures do not recognize the "environment", or see themselves as environmentalists
Benefits of nature environment
The natural environment gives us a wealth of services that are difficult to measure in dollars.
Natural areas help clean our air, purify our water, produce food and medicines, reduce chemical and noise pollution, slow floodwaters, and cool
Food and habitat for wildlife Lizards, fish, frogs and waterbirds feed on wetland plants, small fish, worms, crayfish, and aquatic insects. These smaller animals, along with bacteria, break down dead organisms that sink to the bottom, which produces nutrients that help wetland plants grow.
Improved waterway health Wetlands purify water from drains and natural waterways. Reeds, plants, and algae help filter toxins, chemicals, harmful bacteria and sediment. This is further broken down by small animals and microorganisms in the silt. Cleaner water is then returned to rivers, creeks and waterways.
Good for our wellbeing Wetlands provide food, medicine and materials. In our cities they give us vital green space and a chance to enjoy nature. Wetlands are also spiritually important for Aboriginal people and other cultures.
A more stable climate Wetlands break down and store significant amounts of carbon within their plants and soil, instead of releasing it into the atmosphere as carbon pollution.
Flood control Wetlands soak up excess water from heavy rainfall, which is stored and slowly released back into the environment. Wetland vegetation helps stabilise creek and river banks. Saltmarshes and mangroves help protect our shorelines and river banks by slowing erosion from floods and storm surges.
Negative Impacts of Humans on the Environment
The primary impacts of concern in an energy dependent society often come as a result of our energy use. Burning hydrocarbons like coal and oil to provide us with useful energy results in the emission of carbon dioxide and other pollutants. Other activities causing harm include improper waste disposal to bodies of water and soil, accidental spills of chemicals, increased demand for resources as populations increase (especially due to consumerism), and much more. The impacts that these have on the environment have become clear and include:
Climate change including Global warming
Acid rain, photochemical smog and other forms of pollution
Ocean acidification
Displacement/extinction of wildlife
Resource depletion - forests, water, food
and more.
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