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81-566: In January 1989, Finland sent a letter to the other Arctic states proposing a conference on protection of the Arctic environment . The Rovaniemi Meeting of September 1989 established two working groups. This was followed by the second consultative meeting in Yellowknife , Northwest Territories , Canada in April 1990 where a third ad hoc group was established to develop the strategy. It also resulted in

162-418: A freeboard above the water level. When heavy rains occur, the river or lake fills up. Afterward the dam gradually releases the extra stored water, thus somewhat reducing the height of the flood wave moving down the river. The surface of any stream intersects the surrounding water table. By raising the stream level, the gradient of the surface of the water table above the beaver dam is reduced, and water near

243-520: A polymer of β-glucose monomers . (This creates a more crystalline structure than is found in starch , which is composed of α-glucose monomers. Cellulose is a type of polysaccharide .) Many bacteria produce cellulase which can split off the glucose and use it for energy. Just as algae receive energy from sunlight, these bacteria derive energy from cellulose, and form the base of a very similar food chain. Additionally, bacterial populations absorb nitrogen and phosphorus compounds as they pass by in

324-437: A beaver about 20 minutes to cut down a 15-centimetre (5.9 in) wide aspen, by gnawing a groove around the trunk in an hourglass shape. A beaver's jaws are powerful enough to cut a 1.5-centimetre (0.59 in) sapling in one bite. Maintenance work on the dam and lodges is often done in autumn. If beavers are considered central place foragers , their canals may be considered an extension of their "central place" far beyond

405-441: A capacity to grow , respond to stimuli , reproduce and, through natural selection , adapt to their environment in successive generations. More complex living organisms can communicate through various means. An ecosystem (also called an environment) is a natural unit consisting of all plants, animals, and micro-organisms ( biotic factors) in an area functioning together with all of the non-living physical ( abiotic ) factors of

486-502: A continuum, from 100% natural in one extreme to 0% natural in the other. The massive environmental changes of humanity in the Anthropocene have fundamentally effected all natural environments including: climate change , biodiversity loss and pollution from plastic and other chemicals in the air and water . More precisely, we can consider the different aspects or components of an environment, and see that their degree of naturalness

567-441: A dam, although the average is 10 to 30 centimetres (3.9 to 11.8 in). Log length depends on the diameter of the tree and the size of the beaver. There are recorded cases of beavers felling trees of 45 metres (148 ft) tall and 115 centimetres (45 in) in diameter. Logs of this size are not intended to be used as structural members of the dam; rather, the bark is used for food, and sometimes to get to upper branches. It takes

648-637: A decreased food supply for the wildlife in an area. 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

729-454: A pond from many other aquatic terrain features, such as stream pools and tide pools . Humans impact the water in different ways such as modifying rivers (through dams and stream channelization ), urbanization and deforestation . These impact lake levels, groundwater conditions, water pollution, thermal pollution, and marine pollution . Humans modify rivers by using direct channel manipulation. We build dams and reservoirs and manipulate

810-496: A problem to Earth's ecology as carbon dioxide production. Studies have shown that beaver dams along a stream contribute to denitrification (the conversion of nitrogen compounds back into nitrogen). Bacteria in the dirt and the plant debris, which collects at the dams, turns nitrates into nitrogen gas. The gas bubbles to the surface and mixes with the atmosphere once more. Beaver dams and the associated ponds can provide nurseries for salmon and trout . An early indication of this

891-400: A qualitative and quantitative understanding of the principal areas or spheres of Earth. The Earth's crust or lithosphere , is the outermost solid surface of the planet and is chemically, physically and mechanically different from underlying mantle . It has been generated greatly by igneous processes in which magma cools and solidifies to form solid rock. Beneath the lithosphere lies

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972-621: A remarkable comeback in the United States (after near extirpation in the nineteenth century) and are likely to continually recolonize suitable habitat. Modern solutions include relatively cost-effective and low maintenance flow devices . Introduced to an area without its natural predators, as in Tierra del Fuego , beavers have flooded thousands of acres of land and are considered a plague. One notable difference in Tierra del Fuego from most of North America

1053-430: A river is usually in a channel , made up of a stream bed between banks . In larger rivers there is often also a wider floodplain shaped by waters over-topping the channel. Flood plains may be very wide in relation to the size of the river channel. Rivers are a part of the hydrological cycle . Water within a river is generally collected from precipitation through surface runoff , groundwater recharge , springs and

1134-507: 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 (SO 2 ). The ozone layer of

1215-400: Is 775 metres (2,543 ft) long. Satellite photos provided by NASA WorldWind show the dam did not exist in 1975, but it appeared in subsequent images. It has two or more lodges and is a combination of two original dams. Google Earth images show new dams being built which could ultimately join the main dam and increase the overall length by another 50 to 100 metres (160 to 330 ft) during

1296-436: Is a terrain feature , a body of water that is localized to the bottom of basin . A body of water is considered a lake when it is inland, is not part of an ocean and is larger and deeper than a pond . Natural lakes on Earth are generally found in mountainous areas, rift zones and areas with ongoing or recent glaciation . Other lakes are found in endorheic basins or along the courses of mature rivers. In some parts of

1377-516: Is around 35 parts per thousand (ppt) (3.5%), and nearly all seawater has a salinity in the range of 30 to 38 ppt. Though generally recognized as several separate oceans, these waters comprise one global, interconnected body of salt water often referred to as the World Ocean or global ocean. The deep seabeds are more than half the Earth's surface, and are among the least-modified natural environments. The major oceanic divisions are defined in part by

1458-455: Is found in various kinds of natural body of water . An ocean is a major body of saline water and a component of the hydrosphere. Approximately 71% of the surface of the Earth (an area of some 362 million square kilometers) is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas . More than half of this area is over 3,000 meters (9,800 ft) deep. Average oceanic salinity

1539-785: Is from the Old English wildeornes , which in turn derives from wildeor meaning wild beast (wild + deor = beast, deer). From this point of view, it is the wildness of a place that makes it a wilderness. The mere presence or activity of people does not disqualify an area from being "wilderness". Many ecosystems that are, or have been, inhabited or influenced by activities of people may still be considered "wild". This way of looking at wilderness includes areas within which natural processes operate without very noticeable human interference. Wildlife includes all non- domesticated plants, animals and other organisms. Domesticating wild plant and animal species for human benefit has occurred many times all over

1620-440: 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: In some cultures the term environment is meaningless because there is no separation between people and what they view as

1701-443: Is not uniform. If, for instance, in an agricultural field, the mineralogic composition and the structure of its soil are similar to those of an undisturbed forest soil, but the structure is quite different. Earth science generally recognizes four spheres, the lithosphere , the hydrosphere , the atmosphere and the biosphere as correspondent to rocks , water , air and life respectively. Some scientists include as part of

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1782-528: Is that the trees in Tierra del Fuego cannot be coppiced as can willows, poplars, aspens, and other North American trees. Thus the damage by the beavers seems more severe. The beaver's disruption is not limited to human geography; beavers can destroy nesting habitat for endangered species. Warming temperatures in the Arctic allow beavers to extend their habitat further north, where their dams impair boat travel, impact access to food, affect water quality, and endanger downstream fish populations. Pools formed by

1863-671: Is the application of science and technology to predict the state of the atmosphere for a future time and a given location. The atmosphere is a chaotic system , and small changes to one part of the system can grow to have large effects on the system as a whole. Human attempts to control the weather have occurred throughout human history, and there is evidence that civilized human activity such as agriculture and industry has inadvertently modified weather patterns. Evidence suggests that life on Earth has existed for about 3.7 billion years. All known life forms share fundamental molecular mechanisms, and based on these observations, theories on

1944-430: Is the one originally developed by Wladimir Köppen . The Thornthwaite system , in use since 1948, uses evapotranspiration as well as temperature and precipitation information to study animal species diversity and the potential impacts of climate changes . Weather is a set of all the phenomena occurring in a given atmospheric area at a given time . Most weather phenomena occur in the troposphere , just below

2025-917: The United Kingdom , and the United Nations . Three indigenous peoples ' organizations observed, participated, assisted in developing the strategy, and later became Permanent Participants in the Arctic Council: the Saami Council , the Inuit Circumpolar Conference , and the Association of Indigenous Minorities of the North, Siberia and the Far East of the Russian Federation (RAIPON). They considered

2106-742: The continents , various archipelagos and other criteria, these divisions are : (in descending order of size) the Pacific Ocean , the Atlantic Ocean , the Indian Ocean , the Southern Ocean and the Arctic Ocean . A river is a natural watercourse , usually freshwater , flowing toward an ocean , a lake , a sea or another river. A few rivers simply flow into the ground and dry up completely without reaching another body of water. The water in

2187-408: The mitigation of greenhouse gases that are causing climatic changes, on developing adaptative strategies to global warming, to assist humans, other animal, and plant species, ecosystems, regions and nations in adjusting to the effects of global warming . Some examples of recent collaboration to address climate change and global warming include: A significantly profound challenge is to identify

2268-421: The stratosphere . Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate is the term for the average atmospheric conditions over longer periods of time. When used without qualification, "weather" is understood to be the weather of Earth. Weather occurs due to density (temperature and moisture) differences between one place and another. These differences can occur due to

2349-461: The water table in wetlands such as peatlands , they can stabilize a fluctuating water table, which influences the levels of both carbon and water. In a 2017 study of beaver dam hydrology, monitored beaver dams in a Rocky Mountain peatland were found to increase groundwater storage and regional water balance , which can be beneficial for preventing drought. The study also suggested potential to improve carbon sequestration . Beaver ponds can cause

2430-782: The AEPS in order to deal with sustainable development, and issued the Nuuk Declaration. Another meeting occurred in 1996 in Ottawa , Canada , resulting in the Ottawa Declaration (1996) and the establishment of the Arctic Council . The last meeting, held in 1997 in Alta following the AEPS's 1996 absorption into the Arctic Council resulted in the Alta Declaration. The AEPS remains a strategy for

2511-533: The Council's working groups, including: Critics of the Arctic Environmental Protection Strategy argue that it: Environment (biophysical) The natural environment or natural world encompasses all biotic and abiotic things occurring naturally , meaning in this case not artificial . The term is most often applied to Earth or some parts of Earth. This environment encompasses

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2592-518: 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. 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 are: Within

2673-693: The Rovaniemi ministerial meeting to be "historic" as it represented the first time that Arctic indigenous peoples participated in an international declaration's preparation process. On 14 June 1991, the AEPS and the Declaration on the Protection of the Arctic Environment ("Rovaniemi Declaration") were formally adopted. The main objectives were listed as, "Preserving environmental quality and natural resources, accommodating environmental protection principals with

2754-415: The abiotic constituents of their biotope . A more significant number or variety of species or biological diversity of an ecosystem may contribute to greater resilience of an ecosystem because there are more species present at a location to respond to change and thus "absorb" or reduce its effects. This reduces the effect before the ecosystem's structure changes to a different state. This is not universally

2835-475: The beaver dam flows more slowly into the stream. This may also help in reducing flood waves, and increasing water flow when there is no rain. In other words, beaver dams smooth out water flow by increasing the area wetted by the stream. This allows more water to seep into the ground where its flow is slowed. This water eventually finds its way back to the stream. Rivers with beaver dams in their head waters have lower high water and higher low water levels. By raising

2916-425: The biological manifestation of life is characterized by organization , metabolism , growth , adaptation , response to stimuli and reproduction . Life may also be said to be simply the characteristic state of organisms . In biology , the science of living organisms, "life" is the condition which distinguishes active organisms from inorganic matter , including the capacity for growth, functional activity and

2997-551: The bottom widens. Research is sparse, but it seems likely that parts of the bottomland in North America was created, or at least added to, by the efforts of the generations of beavers that lived there. Humans sometimes build structures similar to beaver dams in streams, either to get the benefits of beaver dams in places without beavers, or to encourage beavers to settle in a particular area. These are often called "beaver dam analogs" (BDA) although other names are also used. When

3078-402: The breakdown of toxins such as pesticides and the retention of silt by beaver dams. Beaver dams reduce erosion and decrease the turbidity that can be a limiting factor for some aquatic life. The benefits may be long-term and largely unnoticed unless a catchment is monitored closely. Almost half of endangered and threatened species in North America rely upon wetlands. In 2012, a systematic review

3159-407: The case and there is no proven relationship between the species diversity of an ecosystem and its ability to provide goods and services on a sustainable level. The term ecosystem can also pertain to human-made environments, such as human ecosystems and human-influenced ecosystems. It can describe any situation where there is relationship between living organisms and their environment. Fewer areas on

3240-425: The continual change preceding death. A diverse variety of living organisms (life forms) can be found in the biosphere on Earth, and properties common to these organisms—plants, animals , fungi , protists , archaea , and bacteria —are a carbon - and water-based cellular form with complex organization and heritable genetic information. Living organisms undergo metabolism , maintain homeostasis , possess

3321-406: The dams store heat, thus changing local hydrology and causing localized thawing of permafrost that in turn contributes to global warming. If a beaver pond becomes too shallow due to sediment accumulation, or the tree supply is depleted, beavers will abandon the site. Eventually the dam will be breached and the water will drain out. The rich thick layer of silt, branches, and dead leaves behind

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3402-624: The direction of the rivers and water path. Dams can usefully create reservoirs and hydroelectric power. However, reservoirs and dams may negatively impact the environment and wildlife. Dams stop fish migration and the movement of organisms downstream. Urbanization affects the environment because of deforestation and changing lake levels, groundwater conditions, etc. Deforestation and urbanization go hand in hand. Deforestation may cause flooding, declining stream flow and changes in riverside vegetation. The changing vegetation occurs because when trees cannot get adequate water they start to deteriorate, leading to

3483-409: The environment. Central to the ecosystem concept is the idea that living organisms are continually engaged in a highly interrelated set of relationships with every other element constituting the environment in which they exist. Eugene Odum , one of the founders of the science of ecology , stated: "Any unit that includes all of the organisms (i.e.: the "community") in a given area interacting with

3564-472: The extinction of natural habitats, which in turn leads to a reduction in wildlife population. The most recent report from the Intergovernmental Panel on Climate Change (the group of the leading climate scientists in the world) concluded that the earth will warm anywhere from 2.7 to almost 11 degrees Fahrenheit (1.5 to 6 degrees Celsius) between 1990 and 2100. Efforts have been increasingly focused on

3645-404: The factors associated with the decline of salmon runs were extant at that time. There are several reasons why beaver dams increase salmon runs. They produce ponds that are deep enough for juvenile salmon to hide from predatory wading birds . They trap nutrients in their ecology and notably the nutrient pulse represented by the migration of the adult salmon upstream. These nutrients help feed

3726-586: The five principal layers determined by temperature there are several layers determined by other properties. The dangers of global warming are being increasingly studied by a wide global consortium of scientists. These scientists are increasingly concerned about the potential long-term effects of global warming on our natural environment and on the planet. Of particular concern is how climate change and global warming caused by anthropogenic , or human-made releases of greenhouse gases , most notably carbon dioxide , can act interactively and have adverse effects upon

3807-412: The flooding occurs next to a railroad roadbed, it can cause derailments by washing out the tracks. When a beaver dam bursts , the resulting flash flood may overwhelm a culvert . Traditional solutions to beaver problems have been focused on the trapping and removal of all the beavers in the area. While this is sometimes necessary, it is typically a short-lived solution, as beaver populations have made

3888-487: The goal is to attract beavers, sometimes the site is unsuitable in its present condition, such as being too eroded for beavers to build a dam in their usual way. BDA builders may use construction techniques beyond the beaver's capabilities, such as driving wooden posts into the stream bed to brace horizontal branches that would otherwise be washed away. The hope is that beavers who wander by or are brought in will choose to live there and take over construction and maintenance of

3969-406: The growth of adventitious roots. Finally the meadow will be colonized by riverine trees, typically aspens, willows and such species which are favoured by the beaver. Beavers are then likely to recolonize the area, and the cycle begins again. Each time the stream life cycle repeats itself another layer of organic soil is added to the bottom of the valley. The valley slowly fills and the flat area at

4050-444: The growth of species of plants that are critical to populations of songbirds in decline, beaver dams help create food and habitat. The presence of beaver dams has been shown to be associated with an increased diversity of songbirds. They can also have positive effects on local waterfowl, such as ducks, that are in need of standing water habitats. Beaver dams can be disruptive; the flooding can cause extensive property damage, and, when

4131-415: The interaction of all living species , climate , weather and natural resources that affect human survival and economic activity. The concept of the natural environment can be distinguished as components: In contrast to the natural environment is the built environment . Built environments are where humans have fundamentally transformed landscapes such as urban settings and agricultural land conversion ,

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4212-864: The juveniles after the yolk sac has been digested. The dams provide calm water which means that the young salmon can use energy for growth rather than for navigating currents; larger smolts with a food reserve have a better rate of survival when they reach the sea. Finally, beaver dams keep the water clear which favours all salmonoids . Beaver dams have been shown to be beneficial to frog and toad populations, likely because they provide protected areas for larvae to mature in warmer, well-oxygenated water. A study in Alberta, Canada, showed that "Pitfall traps on beaver ponds captured 5.7 times more newly metamorphosed wood frogs, 29 times more western toads and 24 times more boreal chorus frogs than on nearby free-flowing streams." Beaver dams help migrating songbirds . By stimulating

4293-535: The lodge, according to a 2004–2012 study that mapped beaver ponds and cut stumps. Some people consider that by building dams beavers are expressing tool use behaviour. Beaver dams typically range in length from a few meters to about 100 metres (330 ft). Canals can be over 0.5 kilometres (1,600 ft) long. The largest known beaver dam is in Wood Buffalo National Park in Alberta , Canada, and

4374-415: The mantle which is heated by the decay of radioactive elements . The mantle though solid is in a state of rheic convection . This convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics . Volcanoes result primarily from the melting of subducted crust material or of rising mantle at mid-ocean ridges and mantle plumes . Most water

4455-412: The natural environment in such a way that the overall ecosystem builds upon the change, making beavers a keystone species and ecosystem engineers . They build prolifically at night, carrying mud with their forepaws and timber between their teeth. A minimum water level of 0.6 to 0.9 metres (2.0 to 3.0 ft) is required to keep the underwater entrance to beaver lodges from being blocked by ice during

4536-524: The natural environment is greatly changed into a simplified human environment. Even acts which seem less extreme, such as building a mud hut or a photovoltaic system in the desert , the modified environment becomes an artificial one. Though many animals build things to provide a better environment for themselves, they are not human, hence beaver dams and the works of mound-building termites are thought of as natural. People cannot find absolutely natural environments on Earth,naturalness usually varies in

4617-410: The natural environmental dynamics in contrast to environmental changes not within natural variances. A common solution is to adapt a static view neglecting natural variances to exist. Methodologically, this view could be defended when looking at processes which change slowly and short time series, while the problem arrives when fast processes turns essential in the object of the study. Climate looks at

4698-436: The natural world, or their surroundings. Specifically in the United States and Arabian countries many native cultures do not recognize the "environment", or see themselves as environmentalists. Beaver dam A beaver dam or beaver impoundment is a dam built by beavers ; it creates a pond which protects against predators such as coyotes, wolves and bears, and holds their food during winter. These structures modify

4779-555: The needs and traditions of Arctic Native peoples, monitoring environmental conditions, and reducing and eventually eliminating pollution in the Arctic Environment." The AEPS outlined five objectives and six pollution issues. Legal issues included its jurisdictional reach and extent of obligations for the member states. Data-gathering, information compilation, and assessment tasks were organized around these issues. In their 1993 follow-up meeting in Nuuk , Greenland , ministers endorsed expanding

4860-567: The next decade. Coordinates: 58°16′15″N 112°15′6″W  /  58.27083°N 112.25167°W  / 58.27083; -112.25167 . Another large beaver dam measuring 2,139 feet (650 m) long, 14 feet (4.3 m) high and 23 feet (7.0 m) thick at the base was found in Three Forks, Montana . Dam building can help to restore damaged wetlands. Wetland benefits include flood control downstream, biodiversity (by providing habitat for different species), and water cleansing, both by

4941-453: The old dam is an ideal habitat for some wetland species. As the wetland fills up with plant debris and dries out, pasture species colonize it and the wetland may eventually become a meadow suitable for grazing in a previously forested area. This provides a valuable niche for many animals which otherwise would be excluded. Beaver dam creation also increases the plants the dams were made from (such as willows) to reproduce by cutting , encouraging

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5022-409: The origin of life attempt to find a mechanism explaining the formation of a primordial single cell organism from which all life originates. There are many different hypotheses regarding the path that might have been taken from simple organic molecules via pre-cellular life to protocells and metabolism. Although there is no universal agreement on the definition of life, scientists generally accept that

5103-438: The physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles (i.e.: exchange of materials between living and nonliving parts) within the system is an ecosystem." The human ecosystem concept is then grounded in the deconstruction of the human/nature dichotomy , and the emergent premise that all species are ecologically integrated with each other, as well as with

5184-400: The planet, and has a major impact on the environment, both positive and negative. Wildlife can be found in all ecosystems. Deserts, rain forests, plains, and other areas—including the most developed urban sites—all have distinct forms of wildlife. While the term in popular culture usually refers to animals that are untouched by civilized human factors, most scientists agree that wildlife around

5265-415: The planet, its natural environment and humans' existence. It is clear the planet is warming, and warming rapidly. This is due to the greenhouse effect , which is caused by greenhouse gases, which trap heat inside the Earth's atmosphere because of their more complex molecular structure which allows them to vibrate and in turn trap heat and release it back towards the Earth. This warming is also responsible for

5346-583: The preparation of a draft document. Kiruna , Sweden was the site of the third meeting, held in January 1991, where one group worked on the drafting the AEPS while another dealt with specific environmental issues . Government officials from all the Arctic nations convened in Rovaniemi in June 1991 for the last consultative meeting. The first three days included meetings, followed by a ministerial-level meeting on 13–14 June observed by representatives from Germany , Poland ,

5427-443: The release of water stored in glaciers and snowpacks. Small rivers may also be called by several other names, including stream , creek and brook. Their current is confined within a bed and stream banks . Streams play an important corridor role in connecting fragmented habitats and thus in conserving biodiversity . The study of streams and waterways in general is known as surface hydrology . A lake (from Latin lacus )

5508-400: The removal of nutrients from the stream flow. Farming along the banks of rivers often increases the loads of phosphates, nitrates and other nutrients, which can cause eutrophication and may contaminate drinking water. Besides silt, the beaver dam collects twigs and branches from the beavers' activity as well as leaves, notably in the autumn . The main component of this material is cellulose ,

5589-627: 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 . 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

5670-495: The statistics of temperature , humidity , atmospheric pressure , wind , rainfall , atmospheric particle count and other meteorological elements in a given region over long periods of time. Weather , on the other hand, is the present condition of these same elements over periods up to two weeks. Climates can be classified according to the average and typical ranges of different variables, most commonly temperature and precipitation. The most commonly used classification scheme

5751-434: The sun angle at any particular spot, which varies by latitude from the tropics. The strong temperature contrast between polar and tropical air gives rise to the jet stream . Weather systems in the mid-latitudes , such as extratropical cyclones , are caused by instabilities of the jet stream flow. Because the Earth's axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of

5832-412: The superstructure. Beavers can transport their own weight in material; they drag logs along mudslides and float them through canals to get them in place. Once the dam has flooded enough area to the proper depth to form a protective moat for the lodge (often covering many acres), beavers begin construction of the lodge. Trees approaching a diameter of 90 centimetres (3.0 ft) may be used to construct

5913-775: The surface of the earth today exist free from human contact, although some genuine wilderness areas continue to exist without any forms of human intervention. Global biogeochemical cycles are critical to life, most notably those of water , oxygen , carbon , nitrogen and phosphorus . Wilderness is generally defined as a natural environment on Earth that has not been significantly modified by human activity. The WILD Foundation goes into more detail, defining wilderness as: "The most intact, undisturbed wild natural areas left on our planet – those last truly wild places that humans do not control and have not developed with roads, pipelines or other industrial infrastructure." Wilderness areas and protected parks are considered important for

5994-420: The survival of certain species , ecological studies, conservation , solitude, and recreation . Wilderness is deeply valued for cultural, spiritual, moral , and aesthetic reasons. Some nature writers believe wilderness areas are vital for the human spirit and creativity. The word, "wilderness", derives from the notion of wildness ; in other words that which is not controllable by humans. The word etymology

6075-457: The water stream and keep these and other nutrients in the beaver pond and the surrounding ecology. Agriculture introduces herbicides and pesticides into streams. Some of these toxicants are metabolized and decomposed by the bacteria in the cellulose-rich bottom of a beaver dam. Some scientists believe that the nitrogen cascade , the production of more fixed nitrogen than the natural cycles can turn back into nitrogen gas, may be as much of

6156-444: The winter. In lakes, rivers and large streams with deep enough water, beavers may not build dams, and live in bank burrows and lodges. Beavers start construction by diverting the stream to lessen the water's flow pressure. Branches and logs are then driven into the mud of the stream bed to form a base. Then sticks, bark (from deciduous trees), rocks, mud, grass, leaves, masses of plants, and anything else available are used to build

6237-411: The world is (now) impacted by human activities. 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

6318-826: The world, there are many lakes because of chaotic drainage patterns left over from the last ice age . All lakes are temporary over geologic time scales, as they will slowly fill in with sediments or spill out of the basin containing them. A pond is a body of standing water , either natural or human-made, that is usually smaller than a lake . A wide variety of human-made bodies of water are classified as ponds, including water gardens designed for aesthetic ornamentation, fish ponds designed for commercial fish breeding and solar ponds designed to store thermal energy. Ponds and lakes are distinguished from streams by their current speed . While currents in streams are easily observed, ponds and lakes possess thermally driven micro-currents and moderate wind-driven currents. These features distinguish

6399-465: The year. On the Earth's surface, temperatures usually range ±40 °C (100 °F to −40 °F) annually. Over thousands of years, changes in the Earth's orbit have affected the amount and distribution of solar energy received by the Earth and influenced long-term climate. Surface temperature differences in turn cause pressure differences. Higher altitudes are cooler than lower altitudes due to differences in compressional heating. Weather forecasting

6480-499: Was conducted on the impacts of beaver dams on fishes and fish habitat (biased to North America (88%)). The most frequently cited benefits of beaver dams were increased habitat heterogeneity , rearing and overwintering habitat, flow refuge, and invertebrate production. Impeded fish movement because of dams, siltation of spawning habitat and low oxygen levels in ponds were the most often cited negative impacts. Benefits (184) were cited more frequently than costs (119). A beaver dam may have

6561-511: Was seen following the 1818 agreement between the British government of Canada and the government of America allowing Americans access to the Columbia watershed. The Hudson's Bay Company , in a fit of pique, instructed its trappers to extirpate the fur-bearing animals in the area. The beaver was the first to be made locally extinct. Salmon runs fell precipitously in the following years, even though none of

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