Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena A phenomenon , plural phenomena, is any observable occurrence. In popular usage, a phenomenon often refers to an extraordinary event. In scientific usage, a phenomenon is any event that is observable, however commonplace it might be, even if it requires the use of instrumentation to observe it. For example, in physics, a phenomenon may be a of the physical world, and also to life Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes (biology) from those that do not, either because such functions have ceased (death), or else because they lack such functions and are classified as inanimate in general. It ranges in scale from the subatomic In physics, subatomic particles are the small particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles. Particle physics and nuclear physics study these particles and how they interact to the cosmic The Universe is commonly defined as the totality of everything that exists, including all physical matter and energy, the planets, stars, galaxies, and the contents of intergalactic space, although this usage may differ with the context . The term Universe may be used in slightly different contextual senses, denoting such concepts as the cosmos,.

The word nature is derived from the Latin word natura, or "essential qualities, innate disposition", and in ancient times, literally meant "birth".^[1] Natura was a Latin translation of the Greek word physis In The Odyssey, Homer uses the word once , referring to the intrinsic way of growth of a particular species of plant. In other very early uses it had such a meaning: related to the natural growing of plants, animals, and other features of the world as they tend to develop without external influence. In the pre-Socratic philosophers it developed a (φύσις), which originally related to the intrinsic characteristics that plants, animals, and other features of the world develop of their own accord.^[2][3] The concept of nature as a whole, the physical universe The Universe is commonly defined as the totality of everything that exists, including all physical matter and energy, the planets, stars, galaxies, and the contents of intergalactic space, although this usage may differ with the context . The term Universe may be used in slightly different contextual senses, denoting such concepts as the cosmos,, is one of several expansions of the original notion; it began with certain core applications of the word φύσις by pre-Socratic philosophers, and has steadily gained currency ever since. This usage was confirmed during the advent of modern scientific method Scientific method refers to a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. To be termed scientific, a method of inquiry must be based on gathering observable, empirical and measurable evidence subject to specific principles of reasoning. A scientific method consists of in the last several centuries.^[4][5]

Within the various uses of the word today, "nature" may refer to the general realm of various types of living plants and animals, and in some cases to the processes associated with inanimate objects–the way that particular types of things exist and change of their own accord, such as the weather Weather is the state of the atmosphere as measured on a scale of hot or cold, wet or dry, calm or storm, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate is the term for the average atmospheric conditions and geology Geology is the science and study of the physical matter and energy that constitute the Earth. The field of geology encompasses the study of the composition, structure, properties, and history of the planet's physical material, the processes by which it is formed, moved, and changed, the history of life on Earth, and human interactions with the of the Earth, and the matter Matter is a general term for the substance of which all physical objects are made. Typically, this includes atoms and other particles which have mass. However in practice there is no single correct scientific meaning; each field uses the term in different and often incompatible ways. A common way of defining matter is as anything that has mass and and energy In physics, energy is a quantity that can be assigned to every particle, object, and system of objects as a consequence of the state of that particle, object or system of objects. Different forms of energy include kinetic, potential, thermal, gravitational, sound, elastic, light, and electromagnetic energy. The forms of energy are often named of which all these things are composed. It is often taken to mean the "natural environment The natural environment, commonly referred to simply as the environment, encompasses all living and non-living things occurring naturally on Earth or some region thereof.[citation needed]" or wilderness Wilderness or wildland is a natural environment on Earth that has not been significantly modified by human activity. It may also be defined 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–wild animals, rocks, forest, beaches, and in general those things that have not been substantially altered by human intervention, or which persist despite human intervention. For, example, manufactured objects and human interaction generally are not considered part of nature, unless qualified as, for example, "human nature" or "the whole of nature". This more traditional concept of natural things which can still be found today implies a distinction between the natural and the artificial, with the artificial being understood as that which has been brought into being by a human consciousness Consciousness is variously defined as subjective experience, or awareness, or wakefulness, or the executive control system of the mind. It is an umbrella term that may refer to a variety of mental phenomena. Although humans realize what everyday experiences are, consciousness refuses to be defined, philosophers note : or a human mind Mind is the aspect of intellect and consciousness experienced as combinations of thought, perception, memory, emotion, will and imagination, including all unconscious cognitive processes. The term is often used to refer, by implication, to the thought processes of reason. Mind manifests itself subjectively as a stream of consciousness. Depending on the particular context, the term "natural" might also be distinguished from the unnatural, the supernatural The term supernatural or supranatural pertains to being above or beyond what one holds to be natural. In the case of one who has strong scientific and atheist beliefs, the supernatural is anything unexplainable by natural law or phenomena. While one who holds mystical or heavenly beliefs may have no conception of supernatural phenomena, he or she, and the artifactual An artifact or artefact is any object made or modified by a human. In archaeology, an artifact is an object recovered by some archaeological endeavor, which may have a cultural interest. Examples include stone tools such as projectile points, pottery vessels, metal objects such as guns, and items of personal adornment such as buttons, jewellery.

Contents 1 Earth 1.1 Geology 1.1.1 Geological evolution 1.2 Historical perspective 2 Atmosphere, climate, and weather 3 Water on Earth 3.1 Oceans 3.2 Lakes 3.2.1 Ponds 3.3 Rivers 3.4 Streams 4 Ecosystems 4.1 Wilderness 5 Life 5.1 Evolution 5.2 Microbes 5.3 Plants and animals 6 Human interrelationship 6.1 Aesthetics and beauty 7 Matter and energy 8 Beyond Earth 9 See also 10 Notes and references 11 External links

Earth

View of the Earth Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet,[note 6] or by its Latin name, Terra.[note 7], taken in 1972 by the Apollo 17 Apollo 17 was the eleventh manned space mission in the NASA Apollo program. It was the first night launch of a U.S. human spaceflight and the sixth and final lunar landing mission of the Apollo program. The mission was launched at 12:33 a.m. EST on December 7, 1972, and concluded on December 19. It remains the most recent manned moon landing and astronaut An astronaut or cosmonaut is a person trained by a human spaceflight program to command, pilot, or serve as a crew member of a spacecraft. While generally reserved for professional space travelers, the term is sometimes applied to anyone who travels into space, including scientists, politicians, journalists, and tourists crew. This image is the only photograph of its kind to date, showing a fully sunlit hemisphere of the Earth. Main articles: Earth Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet,[note 6] or by its Latin name, Terra.[note 7], Earth science Earth science , is an all-embracing term for the sciences related to the planet Earth. It is arguably a special case in planetary science, the Earth being the only known life-bearing planet. There are both reductionist and holistic approaches to Earth sciences. The formal discipline of Earth sciences may include the study of the atmosphere, oceans, Structure of the Earth The interior structure of the Earth, similar to the outer, is layered. These layers can be defined by either their chemical or their rheological properties. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of Earth's, Plate tectonics Plate tectonics is a scientific theory which describes the large scale motions of Earth's lithosphere. The theory builds on the older concepts of continental drift, developed during the first decades of the 20th century by Alfred Wegener, and seafloor spreading, developed in the 1960s, and Geology Geology is the science and study of the physical matter and energy that constitute the Earth. The field of geology encompasses the study of the composition, structure, properties, and history of the planet's physical material, the processes by which it is formed, moved, and changed, the history of life on Earth, and human interactions with the

Earth Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet,[note 6] or by its Latin name, Terra.[note 7] (or, "the earth") is the only planet A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.[a] presently known to support life, and its natural features are the subject of many fields of scientific research. Within the solar system The Solar System[a] consists of the Sun and those celestial objects bound to it by gravity, all of which were formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets[e] whose orbits are almost circular and, it is third nearest to the sun; it is the largest terrestrial planet A terrestrial planet, telluric planet or rocky planet is a planet that is primarily composed of silicate rocks. Within the solar system, the terrestrial planets are the inner planets closest to the Sun. The terms are derived from Latin words for Earth , and an alternative definition would be that these are planets which are, in some notable and the fifth largest overall. Its most prominent climatic features are its two large polar regions, two relatively narrow temperate In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold. But in continental areas, such as central North America the variations between summer and winter can be extreme. In regions zones, and a wide equatorial An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass. The capitalized term Equator refers to the Earth's equator tropical The tropics is a region of the Earth by the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately 23°26' N and the Tropic of Capricorn in the southern hemisphere at 23°26' (23.5°) S. The tropics are also referred to as the tropical zone and the torrid zone (see geographical zone) to subtropical The subtropics are the geographical and climatical zone of the Earth immediately north and south of the tropical zone, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitudes 23.5°N and 23.5°S. The term "subtropical" describes the climatic region found adjacent to the tropics, usually between 20 and 40 region.^[6] Precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that is pulled down by gravity and deposited on the Earth's surface. The main forms of precipitation include rain, snow, ice pellets, and graupel. It occurs when the atmosphere, a large gaseous solution, becomes saturated with water vapour and the water varies widely with location, from several metres The metre , symbol m, is the base unit of length in the International System of Units (SI). Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole, its definition has been periodically refined to reflect growing knowledge of metrology. Since 1983, it is defined as the distance travelled by light in a of water per year to less than a millimetre The millimetre is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length. 71 percent of the Earth's surface is covered by salt-water oceans. The remainder consists of continents and islands, with most of the inhabited land in the Northern Hemisphere The Northern Hemisphere is the half of a planet that is north of equator—the word hemisphere literally means 'half sphere'. It is also that half of the celestial sphere north of the celestial equator. Earth's northern hemisphere contains most of its land area and most of its human population.

Earth has evolved through geological and biological processes that have left traces of the original conditions.^{[citation needed]} The outer surface In geology, a crust is the outermost solid shell of a rocky planet or moon, which is chemically distinct from the underlying mantle. The crusts of Earth, our Moon, Mercury, Venus, Mars, Io, and other planetary bodies have been generated largely by igneous processes, and these crusts are richer in incompatible elements than their respective mantles is divided into several gradually migrating tectonic plates Plate tectonics is a scientific theory which describes the large scale motions of Earth's lithosphere. It is vital for the existence of life on earth because of the role that it plays in the global cycle that maintains the balance of carbon between the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere.[citation needed] The theory, which have changed relatively quickly several times.^{[citation needed]} The interior remains active, with a thick layer of molten mantle The mantle is a part of an astronomical object. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core. Earth's mantle is about 2,890 km thick rocky shell that constitutes about 84 percent of Earth's volume. It is and an iron-filled core that generates a magnetic field Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.

The atmospheric An atmosphere is a layer of gases that may surround a material body of sufficient mass,and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low. Some planets consist mainly of various gases, but only their outer layer is their conditions have been significantly altered from the original conditions by the presence of life-forms,^[7] which create an ecological balance that stabilizes the surface conditions. Despite the wide regional variations in climate by latitude Latitude, usually denoted by the Greek letter phi gives the location of a place on Earth (or other planetary body) north or south of the equator. Lines of Latitude are the imaginary horizontal lines shown running east-to-west (or west to east) on maps (particularly so in the Mercator projection) that run either north or south of the equator and other geographic factors, the long-term average global climate is quite stable during interglacial periods,^[8] and variations of a degree or two of average global temperature have historically had major effects on the ecological balance, and on the actual geography of the Earth.^[9][10]

Geology

Main article: Geology Geology is the science and study of the physical matter and energy that constitute the Earth. The field of geology encompasses the study of the composition, structure, properties, and history of the planet's physical material, the processes by which it is formed, moved, and changed, the history of life on Earth, and human interactions with the Three types of geological plate tectonic Plate tectonics is a scientific theory which describes the large scale motions of Earth's lithosphere. The theory builds on the older concepts of continental drift, developed during the first decades of the 20th century by Alfred Wegener, and seafloor spreading, developed in the 1960s boundaries.

Geology is the science Science is a systematic enterprise of gathering knowledge about nature and organizing and condensing that knowledge into testable laws and theories. As knowledge has increased, some methods have proved more reliable than others, and today the scientific method is the standard for science. It includes the use of careful observation, experimentation, and study of the solid and liquid matter that constitutes the Earth Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet,[note 6] or by its Latin name, Terra.[note 7]. The field of geology encompasses the study of the composition, structure Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover information about the history of deformation in the rocks, and ultimately, to understand the stress field that, physical properties A physical property is any measurable property the value of which describes a physical system's state at any given moment in time. For that reason the changes in the physical properties of a system can be used to describe its transformations, dynamics, and history The history of the Earth describes the most important events and fundamental stages in the development of the planet Earth from its formation 4.6 billion years ago to the present day. Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's past. The age of Earth is approximately one-third of of Earth materials, and the processes by which they are formed, moved, and changed. The field is a major academic discipline, and is also important for mineral and hydrocarbon extraction, knowledge about and mitigation of natural hazards, some engineering fields, and understanding past climates and environments.

Geological evolution

The geology of an area evolves through time as rock units are deposited and inserted and deformational processes change their shapes and locations.^{[citation needed]}

Rock units are first emplaced either by deposition onto the surface or intrude into the overlying rock. Deposition can occur when sediments settle onto the surface of the Earth and later lithify into sedimentary rock, or when as volcanic material such as volcanic ash or lava flows, blanket the surface. Igneous intrusions such as batholiths, laccoliths, dikes, and sills, push upwards into the overlying rock, and crystallize as they intrude.

After the initial sequence of rocks has been deposited, the rock units can be deformed and/or metamorphosed. Deformation typically occurs as a result of horizontal shortening, horizontal extension, or side-to-side (strike-slip) motion. These structural regimes broadly relate to convergent boundaries, divergent boundaries, and transform boundaries, respectively, between tectonic plates.

Historical perspective

Main articles: History of Earth and Evolution An animation of the Earth's hypothesized Pangaea separation. Plankton inhabit oceans, seas and lakes, and have existed on the Earth for at least 2 billion years.^[11]

Earth is estimated to have formed 4.54 billion years ago from the solar nebula, along with the Sun and other planets.^[12] The moon formed roughly 20 million years later. Initially molten, the outer layer of the planet cooled, resulting in the solid crust. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, most or all of which came from ice delivered by comets, produced the oceans and other water sources.^[13] The highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago.^[14]

Continents formed, then broke up and reformed as the surface of Earth reshaped over hundreds of millions of years, occasionally combining to make a supercontinent. Roughly 750 million years ago, the earliest known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia which broke apart about 540 million years ago, then finally Pangaea, which broke apart about 180 million years ago.^[15]

There is significant evidence that a severe glacial action during the Neoproterozoic era covered much of the planet in a sheet of ice. This hypothesis has been termed the "Snowball Earth", and it is of particular interest as it precedes the Cambrian explosion in which multicellular life forms began to proliferate about 530–540 million years ago.^[16]

Since the Cambrian explosion there have been five distinctly identifiable mass extinctions.^[17] The last mass extinction occurred some 65 million years ago, when a meteorite collision probably triggered the extinction of the non-avian dinosaurs and other large reptiles, but spared small animals such as mammals, which then resembled shrews. Over the past 65 million years, mammalian life diversified.^[18]

Several million years ago, a species of small African ape gained the ability to stand upright.^[19] The subsequent advent of human life, and the development of agriculture and further civilization allowed humans to affect the Earth more rapidly than any previous life form, affecting both the nature and quantity of other organisms as well as global climate. By comparison, the oxygen catastrophe, produced by the proliferation of algae during the Siderian period, required about 300 million years to culminate.

The present era is classified as part of a mass extinction event, the Holocene extinction event, the fastest ever to have occurred.^[20][21] Some, such as E. O. Wilson of Harvard University, predict that human destruction of the biosphere could cause the extinction of one-half of all species in the next 100 years.^[22] The extent of the current extinction event is still being researched, debated and calculated by biologists.^[23]

Atmosphere, climate, and weather

Blue light is scattered more than other wavelengths by the gases in the atmosphere, giving the Earth a blue halo when seen from space Main articles: Earth's 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 and other inert gases, carbon dioxide, etc.; but air also contains a variable amount of water vapor. The atmospheric pressure declines steadily with altitude, and has a scale height of about 8 kilometres at the Earth's surface: the height at which the atmospheric pressure has declined by a factor of e (a mathematical constant equal to 2.71...).^[24][25] The ozone layer of the Earth's atmosphere plays an important role in depleting 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.

Terrestrial weather occurs almost exclusively in the lower part of the atmosphere, and serves as a convective system for redistributing heat.^{[citation needed]} Ocean currents are another important factor in determining climate, particularly the major underwater thermohaline circulation which distributes heat energy from the equatorial oceans to the polar regions. These currents help to moderate the differences in temperature between winter and summer in the temperate zones. Also, without the redistributions of heat energy by the ocean currents and atmosphere, the tropics would be much hotter, and the polar regions much colder.

Weather can have both beneficial and harmful effects. Extremes in weather, such as tornadoes or hurricanes and cyclones, can expend large amounts of energy along their paths, and produce devastation. Surface vegetation has evolved a dependence on the seasonal variation of the weather, and sudden changes lasting only a few years can have a dramatic effect, both on the vegetation and on the animals which depend on its growth for their food.

A tornado in central Oklahoma.

The planetary climate is a measure of the long-term trends in the weather.^{[citation needed]} Various factors are known to influence the climate, including ocean currents, surface albedo, greenhouse gases, variations in the solar luminosity, and changes to the planet's orbit. Based on historical records, the Earth is known to have undergone drastic climate changes in the past, including ice ages.

The climate of a region depends on a number of factors, especially latitude. A latitudinal band of the surface with similar climatic attributes forms a climate region. There are a number of such regions, ranging from the tropical climate at the equator to the polar climate in the northern and southern extremes. Weather is also influenced by the seasons, which result from the Earth's axis being tilted relative to its orbital plane. Thus, at any given time during the summer or winter, one part of the planet is more directly exposed to the rays of the sun. This exposure alternates as the Earth revolves in its orbit. At any given time, regardless of season, the northern and southern hemispheres experience opposite seasons.

Weather is a chaotic system that is readily modified by small changes to the environment, so accurate weather forecasting is currently limited to only a few days.^{[citation needed]} Overall, two things are currently happening worldwide: (1) temperature is increasing on the average; and (2) regional climates have been undergoing noticeable changes.^[26]

Water on Earth

The Iguazu waterfalls in the border between Brazil and Argentina. Main article: Water

Water is a chemical substance that is composed of hydrogen and oxygen and is vital for all known forms of life.^[27] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71% of the Earth's surface^[28]. On Earth, it is found mostly in oceans and other large water bodies, with 1.6% of water below ground in aquifers and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation.^[29] Oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers, lakes and ponds 0.6%. Additionally, a minute amount of the Earth's water is contained within biological bodies and manufactured products.

Oceans

A view of the Atlantic ocean from Leblon, Rio de Janeiro. Main article: Ocean

Earth's oceans (World Ocean)
Arctic Ocean Atlantic Ocean Indian Ocean Pacific Ocean Southern Ocean

An ocean is a major body of saline water, and a principal component of the hydrosphere.^{[citation needed]} Approximately 71% of the Earth's surface (an area of some 361 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 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.^[30][31] This concept of a global ocean as a continuous body of water with relatively free interchange among its parts is of fundamental importance to oceanography.^[32]

The major oceanic divisions are defined in part by 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. Smaller regions of the oceans are called seas, gulfs, bays and other names.^{[citation needed]} There are also salt lakes, which are smaller bodies of landlocked saltwater that are not interconnected with the World Ocean. Two notable examples of salt lakes are the Aral Sea and the Great Salt Lake.

Lakes

Lake Mapourika, New Zealand Main article: Lake

A lake (from Latin lacus) is a terrain feature (or physical feature), a body of liquid on the surface of a world that is localized to the bottom of basin (another type of landform or terrain feature; that is, it is not global) and moves slowly if it moves at all.^{[citation needed]} On Earth, a body of water is considered a lake when it is inland, not part of the ocean, is larger and deeper than a pond, and is fed by a river.^[33][34] The only world other than Earth known to harbor lakes is Titan, Saturn's largest moon, which has lakes of ethane, most likely mixed with methane. It is not known if Titan's lakes are fed by rivers, though Titan's surface is carved by numerous river beds. 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 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.

Ponds

The Westborough Reservoir (Mill Pond) in Westborough, Massachusetts. Main article: Pond

A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake.^{[citation needed]} A wide variety of man-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 via current speed. While currents in streams are easily observed, ponds and lakes possess thermally driven microcurrents and moderate wind driven currents. These features distinguish a pond from many other aquatic terrain features, such as stream pools and tide pools.

Rivers

The Nile River in Cairo, Egypt's capital city Main article: River

A river is a natural watercourse^[35], usually freshwater, flowing toward an ocean, a lake, a sea or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, and rill; there is no general rule that defines what can be called a river. Many names for small rivers are specific to geographic location; one example is Burn in Scotland and North-east England. Sometimes a river is said to be larger than a creek,^[36] but this is not always the case, due to vagueness in the language.^[37] A river is part of the hydrological cycle. Water within a river is generally collected from precipitation through surface runoff, groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (i.e., from glaciers).

A rocky stream in Hawaii.

Streams

Main article: Stream

A stream is a flowing body of water with a current, confined within a bed and stream banks.^{[citation needed]} In the United States a stream is classified as a watercourse less than 60 feet (18 metres) wide. Streams are important as conduits in the water cycle, instruments in groundwater recharge, and they serve as corridors for fish and wildlife migration. The biological habitat in the immediate vicinity of a stream is called a riparian zone. Given the status of the ongoing Holocene extinction, 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 and is a core element of environmental geography.^[38]

Ecosystems

Loch Lomond in Scotland forms a relatively isolated ecosystem. The fish community of this lake has remained unchanged over a very long period of time.^[39] An aerial view of a human ecosystem. Pictured is the city of Chicago Main articles: Ecology and Ecosystem

Ecosystems are composed of a variety of abiotic and biotic components that function in an interrelated way.^[40] The structure and composition is determined by various environmental factors that are interrelated. Variations of these factors will initiate dynamic modifications to the ecosystem. Some of the more important components are: soil, atmosphere, radiation from the sun, water, and living organisms.

Central to the ecosystem concept is the idea that living organisms interact with every other element in their local environment.^{[citation needed]} Eugene Odum, a founder of ecology, stated: "Any unit that includes all of the organisms (ie: the "community") in a given area interacting with 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."^[41] Within the ecosystem, species are connected and dependent upon one another in the food chain, and exchange energy and matter between themselves as well as with their environment.^[42] The human ecosystem concept is grounded in the deconstruction of the human/nature dichotomy and the premise that all species are ecologically integrated with each other, as well as with the abiotic constituents of their biotope.^{[citation needed]}

A smaller unit of size is called a microecosystem. For example, a microsystem can be a stone and all the life under it. A macroecosystem might involve a whole ecoregion, with its drainage basin.^[43]

Wilderness

Old growth European Beech forest in Biogradska Gora National Park, Montenegro. Main article: Wilderness

Wilderness is generally defined as areas that have 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 can be found in preserves, estates, farms, conservation preserves, ranches, National Forests, National Parks and even in urban areas along rivers, gulches or otherwise undeveloped areas. Wilderness areas and protected parks are considered important for the survival of certain species, ecological studies, conservation, solitude, and recreation. Some nature writers believe wilderness areas are vital for the human spirit and creativity,^[44] and some Ecologists consider wilderness areas to be an integral part of the planet's self-sustaining natural ecosystem (the biosphere). They may also preserve historic genetic traits and that they provide habitat for wild flora and fauna that may be difficult to recreate in zoos, arboretums or laboratories.

Life

Female mallard and ducklings - reproduction is essential for continuing life Main articles: Life, Biology, and Biosphere

Although there is no universal agreement on the definition of life, scientists generally accept that the biological manifestation of life is characterized by organization, metabolism, growth, adaptation, response to stimuli and reproduction.^[45] Life may also be said to be simply the characteristic state of organisms.

Properties common to terrestrial organisms (plants, animals, fungi, protists, archaea and bacteria) are that they are cellular, carbon-and-water-based with complex organization, having a metabolism, a capacity to grow, respond to stimuli, and reproduce. An entity with these properties is generally considered life. However, not every definition of life considers all of these properties to be essential. Human-made analogs of life may also be considered to be life.

The biosphere is the part of Earth's outer shell – including land, surface rocks, water, air and the atmosphere – within which life occurs, and which biotic processes in turn alter or transform.^{[citation needed]} From the broadest geophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere (rocks), hydrosphere (water), and atmosphere (air). Currently the entire Earth contains over 75 billion tons (150 trillion pounds or about 6.8 x 10¹³ kilograms) of biomass (life), which lives within various environments within the biosphere.^[46]

Over nine-tenths of the total biomass on Earth is plant life, on which animal life depends very heavily for its existence.^[47] More than 2 million species of plant and animal life have been identified to date,^[48] and estimates of the actual number of existing species range from several million to well over 50 million.^[49][50][51] The number of individual species of life is constantly in some degree of flux, with new species appearing and others ceasing to exist on a continual basis.^[52][53] The total number of species is presently in rapid decline.^[54][55][56]

Evolution

An area of the Amazon Rainforest in Brazil. The tropical rainforests of South America contain the largest diversity of species on Earth.^[57][58] Main article: Evolution

Life is only known to exist on the planet Earth. The origin of life is still a poorly understood process, but it is thought to have occurred about 3.9 to 3.5 billion years ago during the hadean or archean eons on a primordial earth that had a substantially different environment than is found at present.^[59] These life forms possessed the basic traits of self-replication and inheritable traits. Once life had appeared, the process of evolution by natural selection resulted in the development of ever-more diverse life forms.

Species that were unable to adapt to the changing environment and competition from other life forms became extinct.^{[citation needed]} However, the fossil record retains evidence of many of these older species. Current fossil and DNA evidence shows that all existing species can trace a continual ancestry back to the first primitive life forms.^[59]

The advent of photosynthesis in very basic forms of plant life worldwide allowed the sun's energy to be harvested to create conditions allowing for more complex life.^{[citation needed]} The resultant oxygen accumulated in the atmosphere and gave rise to the ozone layer. The incorporation of smaller cells within larger ones resulted in the development of yet more complex cells called eukaryotes.^[60] Cells within colonies became increasingly specialized, resulting in true multicellular organisms. With the ozone layer absorbing harmful ultraviolet radiation, life colonized the surface of Earth.

Microbes

A microscopic mite Lorryia formosa. Main article: Microbe

The first form of life to develop on the Earth were microbes, and they remained the only form of life on the planet until about a billion years ago when multi-cellular organisms began to appear.^[61] Microorganisms are single-celled organisms that are generally microscopic, and smaller than the human eye can see. They include Bacteria, Fungi, Archaea and Protista.

These life forms are found in almost every location on the Earth where there is liquid water, including the interior of rocks within the planet.^[62] Their reproduction is both rapid and profuse. The combination of a high mutation rate and a horizontal gene transfer^[63] ability makes them highly adaptable, and able to survive in new environments, including outer space.^[64] They form an essential part of the planetary ecosystem. However some microorganisms are pathogenic and can post health risk to other organisms.

Plants and animals

An example of diverse plant species There are many animal species on the planet. Main articles: Plants and Animals See also: Botany, Fauna, and Biology

Originally Aristotle divided all living things between plants, which generally do not move, and animals. In Linnaeus' system, these became the kingdoms Vegetabilia (later Plantae) and Animalia. Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these are still often considered plants in many contexts. Bacterial life is sometimes included in flora,^[65][66] and some classifications use the term bacterial flora separately from plant flora.

Among the many ways of classifying plants are by regional floras, which, depending on the purpose of study, can also include fossil flora, remnants of plant life from a previous era.^{[citation needed]} People in many regions and countries take great pride in their individual arrays of characteristic flora, which can vary widely across the globe due to differences in climate and terrain.

Regional floras commonly are divided into categories such as native flora and agricultural and garden flora, the lastly mentioned of which are intentionally grown and cultivated.^{[citation needed]} Some types of "native flora" actually have been introduced centuries ago by people migrating from one region or continent to another, and become an integral part of the native, or natural flora of the place to which they were introduced. This is an example of how human interaction with nature can blur the boundary of what is considered nature.

Another category of plant has historically been carved out for weeds.^{[citation needed]} Though the term has fallen into disfavor among botanists as a formal way to categorize "useless" plants, the informal use of the word "weeds" to describe those plants that are deemed worthy of elimination is illustrative of the general tendency of people and societies to seek to alter or shape the course of nature. Similarly, animals are often categorized in ways such as domestic, farm animals, wild animals, pests, etc. according to their relationship to human life.

Animals as a category have several characteristics that generally set them apart from other living things, though not traced by scientists to having legs or wings instead of roots and leaves.^{[citation needed]} Animals are eukaryotic and usually multicellular (although see Myxozoa), which separates them from bacteria, archaea and most protists. They are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls.

With a few exceptions, most notably the sponges (Phylum Porifera), animals have bodies differentiated into separate tissues.^{[citation needed]} These include muscles, which are able to contract and control locomotion, and a nervous system, which sends and processes signals. There is also typically an internal digestive chamber. The eukaryotic cells possessed by all animals are surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells, bones, and spicules, a framework upon which cells can move about and be reorganized during development and maturation, and which supports the complex anatomy required for mobility.

Human interrelationship

Despite their natural beauty, the secluded valleys along the Na Pali Coast in Hawaii are heavily modified by introduced invasive species such as She-oak. Sochi dendrarium is an example of confluence of "natural" and a "made" environment

Although humans currently comprise only a minuscule proportion of the total living biomass on Earth, the human effect on nature is disproportionately large.^{[citation needed]} Because of the extent of human influence, the boundaries between what humans regard as nature and "made environments" is not clear cut except at the extremes. Even at the extremes, the amount of natural environment that is free of discernible human influence is presently diminishing at an increasingly rapid pace.

The development of technology by the human race has allowed the greater exploitation of natural resources and has helped to alleviate some of the risk from natural hazards.^{[citation needed]}In spite of this progress, however, the fate of human civilization remains closely linked to changes in the environment. There exists a highly complex feedback loop between the use of advanced technology and changes to the environment that are only slowly becoming understood.^[67] Man-made threats to the Earth's natural environment include pollution, deforestation, and disasters such as oil spills. Humans have contributed to the extinction of many plants and animals.

Humans employ nature for both leisure and economic activities. The acquisition of natural resources for industrial use remains the primary component of the world's economic system.^{[citation needed]} Some activities, such as hunting and fishing, are used for both sustenance and leisure, often by different people. Agriculture was first adopted around the 9th millennium BCE. Ranging from food production to energy, nature influences economic wealth.

Although early humans gathered uncultivated plant materials for food and employed the medicinal properties of vegetation for healing,^[68] most modern human use of plants is through agriculture. The clearance of large tracts of land for crop growth has led to a significant reduction in the amount available of forestation and wetlands, resulting in the loss of habitat for many plant and animal species as well as increased erosion.^[69]

Aesthetics and beauty

Pinguicula grandiflora, commonly known as a Butterwort Summer field in Belgium (Hamois). The blue flower is Centaurea cyanus and the red one a Papaver rhoeas.

Beauty in nature has historically been a prevalent theme in art and books, filling large sections of libraries and bookstores. That nature has been depicted and celebrated by so much art, photography, poetry and other literature shows the strength with which many people associate nature and beauty. Reasons why this association exists, and what the association consists of, is studied by the branch of philosophy called aesthetics. Beyond certain basic characteristics that many philosophers agree about to explain what is seen as beautiful, the opinions are virtually endless.^[70] Nature and wildness have been important subjects in various epochs of world history. An early tradition of landscape art began in China during the Tang Dynasty (618-907). The tradition of representing nature as it is became one of the aims of Chinese painting and was a significant influence in Asian art.

Wilderness portrayals in art became more prevalent in the 1800s, especially in the works of the Romantic movement. British artists John Constable and JMW Turner turned their attention to capturing the beauty of the natural world in their paintings. Before that, paintings had been primarily of religious scenes or of human beings. William Wordsworth's poetry described the wonder of the natural world, which had formerly been viewed as a threatening place. Increasingly the valuing of nature became an aspect of Western culture.^[71] This artistic movement also coincided with the Transcendentalist movement in the Western world. A common classical idea of beautiful art involves the word mimesis, the imitation of nature. Also in the realm of ideas about beauty in nature is that the perfect is implied through symmetry, equal division, and other perfect mathematical forms and notions.^{[citation needed]}

Matter and energy

The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density Main articles: Matter and Energy See also: Chemistry and Physics

Some fields of science see nature as matter in motion, obeying certain laws of nature which science seeks to understand. For this reason the most fundamental science is generally understood to be "physics" – the name for which is still recognizable as meaning that it is the study of nature.^{[citation needed]}

Matter is commonly defined as the substance of which physical objects are composed. It constitutes the observable universe. The visible components of the universe are now believed to compose only 4 percent of the total mass. The remainder is believed to consist of 23 percent cold dark matter and 73 percent dark energy.^[72] The exact nature of these components is still unknown and is currently under intensive investigation by physicists.

The behavior of matter and energy throughout the observable universe appears to follow well-defined physical laws. These laws have been employed to produce cosmological models that successfully explain the structure and the evolution of the universe we can observe. The mathematical expressions of the laws of physics employ a set of twenty physical constants^[73] that appear to be static across the observable universe.^[74] The values of these constants have been carefully measured, but the reason for their specific values remains a mystery.

Beyond Earth

Planets and dwarf planets of the Solar System (Sizes to scale, distances not to scale) The deepest visible-light image of the universe from the Hubble Ultra Deep Field telescope NGC 4414 is a spiral galaxy in the constellation Coma Berenices about 56,000 light years in diameter and approximately 60 million light years from Earth Main articles: Outer space, Universe, and Extraterrestrial life

Outer space, also simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. Outer space is used to distinguish it from airspace (and terrestrial locations). There is no discrete boundary between the Earth's atmosphere and space, as the atmosphere gradually attenuates with increasing altitude. Outer space within the solar system is called interplanetary space, which passes over into interstellar space at what is known as the heliopause.

Outer space is certainly spacious, but it is far from empty.^{[citation needed]} Outer space is sparsely filled with several dozen types of organic molecules discovered to date by microwave spectroscopy, blackbody radiation left over from the big bang and the origin of the universe, and cosmic rays, which include ionized atomic nuclei and various subatomic particles. There is also some gas, plasma and dust, and small meteors. Additionally, there are signs of human life in outer space today, such as material left over from previous manned and unmanned launches which are a potential hazard to spacecraft. Some of this debris re-enters the atmosphere periodically.

Although the planet Earth is currently the only known body within the solar system to support life, current evidence suggests that in the distant past the planet Mars possessed bodies of liquid water on the surface.^[75] For a brief period in Mars' history, it may have also been capable of forming life. At present though, most of the water remaining on Mars is frozen. If life exists at all on Mars, it is most likely to be located underground where liquid water can still exist.^[76]

Conditions on the other terrestrial planets, Mercury and Venus, appear to be too harsh to support life as we know it.^{[citation needed]} But it has been conjectured that Europa, the fourth-largest moon of Jupiter, may possess a sub-surface ocean of liquid water and could potentially host life.^[77]

Recently, the team of Stéphane Udry have discovered a new planet named Gliese 581 d, which is an extrasolar planet orbiting the red dwarf star Gliese 581.^{[citation needed]} Gliese 581 d appears to lie in the habitable zone of space surrounding the star, and therefore could possibly host life as we know it.

See also

	Environment portal
	Ecology portal
	Earth sciences portal
	Weather portal
	Astronomy portal

Science:

• Natural history
• Natural science
• Natural landscape

Philosophy:

• Mother Nature
• Nature (philosophy)
• Naturalism (philosophy): any of several philosophical stances, typically those descended from Materialism and Pragmatism that do not distinguish the supernatural from nature.^{[citation needed]} This includes the methodological naturalism of natural science, which makes the methodological assumption that observable events in nature are explained only by natural causes, without assuming either the existence or non-existence of the supernatural.
• Balance of nature (biological fallacy): A discredited concept of natural equilibrium in predator:prey dynamics.

Media: Natural History, by Pliny the Elder Nature, by Ralph Waldo Emerson Nature, a prominent scientific journal National Wildlife Magazine, publication of the National Wildlife Federation Nature (TV series)

Organizations: The Nature Conservancy Nature Detectives

Notes and references

Landscape photograph of Tolima Colombia. Taiga forest in winter, Arkhangelsk Oblast, Russia. Atmospheric gases scatter blue wavelengths of visible light more than other wavelengths, giving the Earth’s visible edge a blue halo. Credit: NASA's Earth Observatory. A deserted island in Palau. Two Giant Sequoias, Sequoia National Park. Note the large fire scar at the base of the right-hand tree; fires do not kill the trees but do remove competing thin-barked species, and aid Giant Sequoia regeneration. A Riparian zone along Trout Creek in the Trout Creek Mountains; part of the Burns Bureau of Land Management District in southeastern Oregon.

1. ^ Harper, Douglas. "nature". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=nature. Retrieved 2006-09-23.
2. ^ A useful though somewhat erratically presented account of the pre-Socratic use of the concept of φύσις may be found in Naddaf, Gerard The Greek Concept of Nature, SUNY Press, 2006. The word φύσις, while first used in connection with a plant in Homer, occurs very early in Greek philosophy, and in several senses. Generally, these senses match rather well the current senses in which the English word nature is used, as confirmed by Guthrie, W.K.C. Presocratic Tradition from Parmenides to Democritus (volume 2 of his History of Greek Philosophy), Cambridge UP, 1965.
3. ^ The first known use of physis was by Homer in reference to the intrinsic qualities of a plant: ὣς ἄρα φωνήσας πόρε φάρμακον ἀργεϊφόντης ἐκ γαίης ἐρύσας, καί μοι φύσιν αὐτοῦ ἔδειξε. (So saying, Argeiphontes [=Hermes] gave me the herb, drawing it from the ground, and showed me its nature.) Odyssey 10.302-3 (ed. A.T. Murray). (The word is dealt with thoroughly in Liddell and Scott's Greek Lexicon.) For later but still very early Greek uses of the term, see earlier note.
4. ^ Isaac Newton's Philosophiae Naturalis Principia Mathematica (1687), for example, is translated "Mathematical Principles of Natural Philosophy", and reflects the then-current use of the words "natural philosophy", akin to "systematic study of nature"
5. ^ The etymology of the word "physical" shows its use as a synonym for "natural" in about the mid-15th century: Harper, Douglas. "physical". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=physical. Retrieved 2006-09-20.
6. ^ "World Climates". Blue Planet Biomes. http://www.blueplanetbiomes.org/climate.htm. Retrieved 2006-09-21.
7. ^ "Calculations favor reducing atmosphere for early Earth". Science Daily. 2005-09-11. http://www.sciencedaily.com/releases/2005/09/050911103921.htm. Retrieved 2007-01-06.
8. ^ "Past Climate Change". U.S. Environmental Protection Agency. http://www.epa.gov/climatechange/science/pastcc.html. Retrieved 2007-01-07.
9. ^ Hugh Anderson, Bernard Walter (March 28, 1997). "History of Climate Change". NASA. http://web.archive.org/web/20080123130745/http://vathena.arc.nasa.gov/curric/land/global/climchng.html. Retrieved 2007-01-07.
10. ^ Weart, Spencer (June 2006). "The Discovery of Global Warming". American Institute of Physics. http://www.aip.org/history/climate/. Retrieved 2007-01-07.
11. ^ Margulis, Lynn; Dorian Sagan (1995). What is Life?. New York: Simon & Schuster. ISBN 0684813262.
12. ^ Dalrymple, G. Brent (1991). The Age of the Earth. Stanford: Stanford University Press. ISBN 0-8047-1569-6.
13. ^ Morbidelli, A.; et al. (2000). "Source Regions and Time Scales for the Delivery of Water to Earth". Meteoritics & Planetary Science 35 (6): 1309–1320. doi:10.1111/j.1945-5100.2000.tb01518.x. http://adsabs.harvard.edu/abs/2000M&PS...35.1309M.
14. ^ "Earth's Oldest Mineral Grains Suggest an Early Start for Life". NASA Astrobilogy Institute. 2001-12-24. http://nai.arc.nasa.gov/news_stories/news_detail.cfm?ID=76. Retrieved 2006-05-24.
15. ^ Murphy, J.B.; R.D. Nance (2004). (). American Scientist 92 (4): 324. doi:10.1511/2004.4.324. .
16. ^ Kirschvink, J.L. (1992). "Late Proterozoic Low-Latitude Global Glaciation: The Snowball Earth". in J.W. Schopf, C. Klein eds.. The Proterozoic Biosphere. Cambridge: Cambridge University Press. pp. 51–52. ISBN 0-521-36615-1. http://www.gps.caltech.edu/~jkirschvink/pdfs/firstsnowball.pdf.
17. ^ Raup, David M.; J. John Sepkoski Jr. (March 1982). "Mass extinctions in the marine fossil record". Science 215 (4539): 1501. doi:10.1126/science.215.4539.1501. PMID 17788674.
18. ^ Margulis, Lynn; Dorian Sagan (1995). What is Life?. New York: Simon & Schuster. pp. 145. ISBN 0-684-81326-2.
19. ^ Margulis, Lynn; Dorian Sagan (1995). What is Life?. New York: Simon & Schuster. ISBN 0-684-81326-2.
20. ^ Diamond J; Ashmole, N. P.; Purves, P. E. (1989). "The present, past and future of human-caused extinctions". Philos Trans R Soc Lond B Biol Sci 325 (1228): 469–76; discussion 476–7. doi:10.1098/rstb.1989.0100. PMID 2574887.
21. ^ Novacek M, Cleland E (2001). "The current biodiversity extinction event: scenarios for mitigation and recovery". Proc Natl Acad Sci USA 98 (10): 1029. doi:10.1073/pnas.091093698. PMID 11344295.
22. ^ "The mid-Holocene extinction of silver fir (Abies alba) in the ..." pdf
23. ^ See, e.g. [1], [2], [3]
24. ^ "Ideal Gases under Constant Volume, Constant Pressure, Constant Temperature, & Adiabatic Conditions". NASA. http://www.grc.nasa.gov/WWW/K-12/Numbers/Math/Mathematical_Thinking/ideal_gases_under_constant.htm. Retrieved 2007-01-07.
25. ^ Pelletier, Jon D. (2002). "Natural variability of atmospheric temperatures and geomagnetic intensity over a wide range of time scales". Proceedings of the National Academy of Sciences 99: 2546–2553. doi:10.1073/pnas.022582599. PMID 11875208.
26. ^ "Tropical Ocean Warming Drives Recent Northern Hemisphere Climate Change". Science Daily. April 6, 2001. http://www.sciencedaily.com/releases/2001/04/010406073554.htm. Retrieved 2006-05-24.
27. ^ United Nations
28. ^ "CIA- The world fact book". Central Intelligence Agency. https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html#Geo. Retrieved 2008-12-20.
29. ^ Water Vapor in the Climate System, Special Report, [AGU], December 1995 (linked 4/2007). Vital Water UNEP.
30. ^ "Ocean". The Columbia Encyclopedia. 2002. New York: Columbia University Press
31. ^ "Distribution of land and water on the planet". UN Atlas of the Oceans
32. ^ Spilhaus, Athelstan F. 1942 (Jul.). "Maps of the whole world ocean." Geographical Review (American Geographical Society). Vol. 32 (3): pp. 431-5.
33. ^ Brittanica online. "Lake (physical feature)". http://www.britannica.com/EBchecked/topic/328083/lake. Retrieved 2008-06-25. "[a Lake is] any relatively large body of slowly moving or standing water that occupies an inland basin of appreciable size. Definitions that precisely distinguish lakes, ponds, swamps, and even rivers and other bodies of nonoceanic water are not well established. It may be said, however, that rivers and streams are relatively fast moving; marshes and swamps contain relatively large quantities of grasses, trees, or shrubs; and ponds are relatively small in comparison to lakes. Geologically defined, lakes are temporary bodies of water."
34. ^ [http://dictionary.reference.com/browse/lake a body of fresh or salt water of considerable size, surrounded by land. "Dictionary.com definition"]. http://dictionary.reference.com/browse/lake a body of fresh or salt water of considerable size, surrounded by land.. Retrieved 2008-06-25.
35. ^ River {definition} from Merriam-Webster. Accessed February 2010.
36. ^ River, Wordnet
37. ^ USGS - U.S. Geological Survey - faqs, #17 What is the difference between mountain, hill, and peak; lake and pond; or river and creek?
38. ^ http://ga.water.usgs.gov/edu/hydrology.html/
39. ^ Adams, C.E. (1994). "The fish community of Loch Lomond, Scotland : its history and rapidly changing status". Hydrobiologia 290 (1-3): 91–102. doi:10.1007/BF00008956. http://cat.inist.fr/?aModele=afficheN&cpsidt=3302548.
40. ^ Pidwirny, Michael (2006). "Introduction to the Biosphere: Introduction to the Ecosystem Concept". Fundamentals of Physical Geography (2nd Edition). http://www.physicalgeography.net/fundamentals/9j.html. Retrieved September 28, 2006.
41. ^ Odum, EP (1971) Fundamentals of ecology, third edition, Saunders New York
42. ^ Pidwirny, Michael (2006). "Introduction to the Biosphere: Organization of Life". Fundamentals of Physical Geography (2nd Edition). http://www.physicalgeography.net/fundamentals/9d.html. Retrieved September 28, 2006.
43. ^ Bailey, Robert G. (April 2004). "Identifying Ecoregion Boundaries" (PDF). Environmental Management 34 (Supplement 1): S14. doi:10.1007/s00267-003-0163-6. PMID 15883869. http://www.fs.fed.us/institute/news_info/Identifying_ecoregion_boundaries.pdf.
44. ^ No Man's Garden by Daniel B. Botkin p155-157
45. ^ "Definition of Life". California Academy of Sciences. 2006. http://www.calacademy.org/exhibits/xtremelife/what_is_life.php. Retrieved 2007-01-07.
46. ^ The figure "about one-half of one percent" takes into account the following (See, e.g., Leckie, Stephen (1999). "How Meat-centred Eating Patterns Affect Food Security and the Environment". For hunger-proof cities : sustainable urban food systems. Ottawa: International Development Research Centre. ISBN 0-88936-882-1. http://www.idrc.ca/en/ev-30610-201-1-DO_TOPIC.html. , which takes global average weight as 60 kg.), the total human biomass is the average weight multiplied by the current human population of approximately 6.5 billion (see, e.g., "World Population Information". U.S. Census Bureau. http://www.census.gov/ipc/www/world.html. Retrieved September 28, 2006. ): Assuming 60–70 kg to be the average human mass (approximately 130–150 lb on the average), an approximation of total global human mass of between 390 billion (390×10⁹) and 455 billion kg (between 845 billion and 975 billion lb, or about 423 million–488 million short tons). The total biomass of all kinds on earth is estimated to be in excess of 6.8 x 10¹³ kg (75 billion short tons). By these calculations, the portion of total biomass accounted for by humans would be very roughly 0.6%.
47. ^ Sengbusch, Peter V.. "The Flow of Energy in Ecosystems - Productivity, Food Chain, and Trophic Level". Botany online. University of Hamburg Department of Biology. http://www.biologie.uni-hamburg.de/b-online/e54/54c.htm. Retrieved September 23, 2006.
48. ^ Pidwirny, Michael (2006). "Introduction to the Biosphere: Species Diversity and Biodiversity". Fundamentals of Physical Geography (2nd Edition). http://www.physicalgeography.net/fundamentals/9h.html. Retrieved September 23, 2006.
49. ^ "How Many Species are There?". Extinction Web Page Class Notes. http://faculty.plattsburgh.edu/thomas.wolosz/howmanysp.htm. Retrieved September 23, 2006.
50. ^ "Animal." World Book Encyclopedia. 16 vols. Chicago: World Book, 2003. This source gives an estimate of from 2–50 million.
51. ^ "Just How Many Species Are There, Anyway?". Science Daily. May 2003. http://www.sciencedaily.com/releases/2003/05/030526103731.htm. Retrieved September 26, 2006.
52. ^ Withers, Mark A.; et al. (1998). "Changing Patterns in the Number of Species in North American Floras". Land Use History of North America. http://biology.usgs.gov/luhna/chap4.html. Retrieved September 26, 2006. Website based on the contents of the book: Sisk, T.D., ed., ed (1998). Perspectives on the land use history of North America: a context for understanding our changing environment (Revised September 1999 ed.). U.S. Geological Survey, Biological Resources Division. USGS/BRD/BSR-1998-0003.
53. ^ "Tropical Scientists Find Fewer Species Than Expected". Science Daily. April 2002. http://www.sciencedaily.com/releases/2002/04/020425072847.htm. Retrieved September 27, 2006.
54. ^ Bunker, Daniel E.; et al. (November 2005). "Species Loss and Aboveground Carbon Storage in a Tropical Forest". Science 310 (5750): 1029–31. doi:10.1126/science.1117682. PMID 16239439. http://www.sciencemag.org/cgi/content/abstract/310/5750/1029.
55. ^ Wilcox, Bruce A. (March 2006). "Amphibian Decline: More Support for Biocomplexity as a Research Paradigm". EcoHealth 3 (1): 1. doi:10.1007/s10393-005-0013-5. http://www.springerlink.com/content/810227460032m460/.
56. ^ Clarke, Robin, Robert Lamb, Dilys Roe Ward eds., ed (2002). "Decline and loss of species". Global environment outlook 3 : past, present and future perspectives. London; Sterling, VA: Nairobi, Kenya : UNEP. ISBN 92-807-2087-2. http://www.grida.no/geo/geo3/english/221.htm.
57. ^ http://earthobservatory.nasa.gov/Newsroom/view.php?id=28907
58. ^ http://www.sciencedaily.com/releases/2005/12/051205163236.htm
59. ^ ^{a b} Line M (1 January 2002). "The enigma of the origin of life and its timing". Microbiology 148 (Pt 1): 21–7. PMID 11782495. http://mic.sgmjournals.org/cgi/content/full/148/1/21?view=long&pmid=11782495.
60. ^ Berkner, L. V.; L. C. Marshall (May 1965). "On the Origin and Rise of Oxygen Concentration in the Earth's Atmosphere". Journal of the Atmospheric Sciences 22 (3): 225–261. doi:10.1175/1520-0469(1965)022<0225:OTOARO>2.0.CO;2. http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0469(1965)022%3C0225:OTOARO%3E2.0.CO%3B2.
61. ^ Schopf J (1994). "Disparate rates, differing fates: tempo and mode of evolution changed from the Precambrian to the Phanerozoic." (PDF). Proc Natl Acad Sci USA 91 (15): S14. doi:10.1073/pnas.91.15.6735. PMID 8041691. PMC 44277. http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=44277&blobtype=pdf.
62. ^ Szewzyk U, Szewzyk R, Stenström T (1994). "Thermophilic, anaerobic bacteria isolated from a deep borehole in granite in Sweden.". Proc Natl Acad Sci USA 91 (5): 1810–3. doi:10.1073/pnas.91.5.1810. PMID 11607462.
63. ^ Wolska K (2003). "Horizontal DNA transfer between bacteria in the environment.". Acta Microbiol Pol 52 (3): 233–43. PMID 14743976.
64. ^ Horneck G (1981). "Survival of microorganisms in space: a review.". Adv Space Res 1 (14): 39–48. doi:10.1016/0273-1177(81)90241-6. PMID 11541716.
65. ^ "flora". Merriam-Webster Online Dictionary. Merriam-Webster. http://webster.com/cgi-bin/dictionary?va=flora. Retrieved September 27, 2006.
66. ^ "Glossary". Status and Trends of the Nation's Biological Resources. Reston, VA: Department of the Interior, Geological Survey. 1998. SuDocs No. I 19.202:ST 1/V.1-2. http://biology.usgs.gov/s+t/SNT/noframe/zy198.htm#F.
67. ^ "Feedback Loops In Global Climate Change Point To A Very Hot 21st Century". Science Daily. May 22, 2006. http://www.lbl.gov/Science-Articles/Archive/ESD-feedback-loops.html. Retrieved 2007-01-07.
68. ^ "Plant Conservation Alliance - Medicinal Plant Working Groups Green Medicine". US National Park Services. http://www.nps.gov/plants/medicinal/plants.htm. Retrieved September 23, 2006.
69. ^ Oosthoek, Jan (1999). "Environmental History: Between Science & Philosophy". Environmental History Resources. http://www.eh-resources.org/philosophy.html. Retrieved 2006-12-01.
70. ^ For an example of a range of opinions, see: "On the Beauty of Nature". The Wilderness Society. http://www.wilderness.org/Library/Documents/Beauty_Quotes.cfm. Retrieved September 29, 2006. and Ralph Waldo Emerson's analysis of the subject: Emerson, Ralph Waldo (1849). "Beauty". Nature; Addresses and Lectures. http://www.emersoncentral.com/beauty.htm.
71. ^ History of Conservation BC Spaces for Nature. Accessed: May 20, 2006.
72. ^ "Some Theories Win, Some Lose". WMAP Mission: First Year Results. NASA. http://map.gsfc.nasa.gov/m_mm/mr_limits.html. Retrieved 29 2006.
73. ^ Taylor, Barry N. (1971). "Introduction to the constants for nonexperts". National Institute of Standards and Technology. http://www.physics.nist.gov/cuu/Constants/introduction.html. Retrieved 2007-01-07.
74. ^ D. A. Varshalovich, A. Y. Potekhin, A. V. Ivanchik (2000). "Testing cosmological variability of fundamental constants". AIP Conference Proceedings 506: 503. doi:10.1063/1.1302777. http://arxiv.org/abs/physics/0004062.
75. ^ Bibring, J; Langevin Y, Mustard J, Poulet F, Arvidson R, Gendrin A, Gondet B, Mangold N, Pinet P, Forget F, Berthé M, Bibring J, Gendrin A, Gomez C, Gondet B, Jouglet D, Poulet F, Soufflot A, Vincendon M, Combes M, Drossart P, Encrenaz T, Fouchet T, Merchiorri R, Belluci G, Altieri F, Formisano V, Capaccioni F, Cerroni P, Coradini A, Fonti S, Korablev O, Kottsov V, Ignatiev N, Moroz V, Titov D, Zasova L, Loiseau D, Mangold N, Pinet P, Douté S, Schmitt B, Sotin C, Hauber E, Hoffmann H, Jaumann R, Keller U, Arvidson R, Mustard J, Duxbury T, Forget F, Neukum G (2006). "Global mineralogical and aqueous mars history derived from OMEGA/Mars Express data". Science 312 (5772): 400–4. doi:10.1126/science.1122659. PMID 16627738.
76. ^ Malik, Tariq (2005-03-08). "Hunt for Mars life should go underground". The Brown University News Bureau. http://www.msnbc.msn.com/id/7129347/. Retrieved September 4, 2006.
77. ^ Scott Turner (1998-03-02). "Detailed Images From Europa Point To Slush Below Surface". The Brown University News Bureau. http://www2.jpl.nasa.gov/galileo/news8.html. Retrieved September 28, 2006.

External links

	Book:Nature
Books are collections of articles that can be downloaded or ordered in print.

Find more about Nature on Wikipedia's sister projects:
	Definitions from Wiktionary
	Textbooks from Wikibooks
	Quotations from Wikiquote
	Source texts from Wikisource
	Images and media from Commons
	News stories from Wikinews
	Learning resources from Wikiversity

• Nature Journal - Weekly journal of science.
• The WILD Foundation.
• BBC - Science and Nature.
• European Commission - Nature and Biodiversity homepage.
• The Nature Conservancy
• Science.gov - Environment & Environmental Quality.
• wallpapers nature.
• NatureWatch - Wiki for documenting biodiversity (german)
• Ministry of Environment Republic of Korea - Nature

The Dynamic Earth Continents Africa • Antarctica • Asia • Europe • North America • Australia • South America Oceans Arctic Ocean • Atlantic Ocean • Indian Ocean • Pacific Ocean • Southern Ocean Dynamic Earth Earth science • Future of the Earth • Geological history of Earth • Geology • History of the Earth • Plate tectonics • Structure of the Earth Natural Environment Biome • Ecology • Ecosystem • Nature • Wilderness Related Articles Earth Day • Geology of solar terrestrial planets • Solar System • World Category · Portal

Elements of nature Universe Space · Time · Matter · Energy Earth Earth science · Geology · History of the Earth · Geological history of Earth · Future of the Earth · Structure of the Earth · Plate tectonics Weather Earth's atmosphere · Climate · Meteorology Environment Ecology · Ecosystem · Wilderness Life Hierarchy of life · Origin of life · Life on Earth · Eukaryota (Plants/Flora, Animals/Fauna, Fungi, Protista) · Prokaryote (Archaea, Bacteria) · Virus · Evolutionary history of life · Biology Category · Portal

Fields within the natural sciences Astronomy · Physics · Earth science · Chemistry · Biology

Environmental science Atmospheric sciences · Ecology · Geosciences · Soil science · Hydrology Related fields: Biology · Chemistry · Environmental design · Environmental economics · Environmental ethics · Environmental history · Environmental law · Environmental politics · Environmental sociology · Environmental studies · Physics · Pollution control · Sustainability · Waste management Environmental technology

Major subfields of biology Anatomy · Astrobiology · Biochemistry · Biomechanics · Biophysics · Bioinformatics · Biostatistics · Botany · Cell biology · Chemical biology · Chronobiology · Conservation biology · Developmental biology · Ecology · Epidemiology · Evolutionary biology · Genetics · Genomics · Histology · Human biology · Immunology · Marine biology · Mathematical biology · Microbiology · Molecular biology · Mycology · Neuroscience · Nutrition · Origin of life · Paleontology · Parasitology · Pathology · Pharmacology · Physiology · Quantum biology · Systems biology · α-Taxonomy · Toxicology · Zoology

Categories: Nature | Environmental science

 

 

See Also:

 

What Links Here:

 

Recently Viewed Pages:

• Home
• Science: Agriculture: Field Crops: Cereals: Sorghum: Pests and Diseases: Directory
• Biotechnology: Blogs
• Cocoa Bean: Encyclopedia
• Rye: Answers
• Cash Crop: Answers
• Cocoa Bean: Images
• Root Crops: Encyclopedia
• Science: Agriculture: Field Crops: Root Crops
• Sugar Beet: Answers

 

Most Popular Pages:

• Monoculture: Answers
• Oilseeds: Blogs
• Science: Agriculture: Field Crops: Cereals: Sorghum: Pests and Diseases: Directory
• Sugar Beet: Answers
• Subsistence Agriculture: Encyclopedia
• Cash Crop: Answers
• Category:Agricultural Terminology: Blogs
• Post-harvest Handling: News
• Rye: Answers
• Barley: Answers

Related 'Nature' Searches:

related terms:	Nature	Geology	Natura	Physical
	Earth Atmosphere	Atmosphere Climate	Earth Surface	Animals
	Wilderness	Surface Water	Natural	Plants

---

top user searches:	►

---

or search for "Nature" in:		Web:		The Entire Web	Related Sites	Web Directories
		This Site:		Page Titles	Karr Network Sites*
		News:		Headlines	Weather	Events	Blogs
		Reference:		Encyclopedia	Dictionary	eTexts	Quotes
				Local Map	Answers
		Multimedia:		Images	Videos
		People:		Discussion Groups	Social Networking
		Shopping:		General Merch.	Consumer Opinion	Auctions	Classifieds

 

---

The Entire Web Web Directories Related* Sites Karr Network Sites* Page Titles Headlines Weather Events Blogs Encyclopedia Dictionary eTexts Quotes Answers Local Map Videos Images Social Networking Discussion Groups General Items Auctions Classifieds Consumer Opinion

Sitemap News Dictionary Encyclopedia Blogs Answers Videos Images Shopping Directory More…