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Details of Nature

Nature, in the broadest sense, is equivalent to the natural world, physical universe, material world or material universe. "Nature" refers to the phenomena of the physical world, and also to life in general. The term generally does not include manufactured objects and human interaction unless qualified in ways such as, e.g., "human nature" or "the whole of nature". Nature is also generally distinguished from the supernatural. It ranges in scale from the subatomic to the galactic.

The word "nature" is derived from the Latin word natura, or "the course of things, natural character." Natura was a Latin translation of the Greek word physis (φύσις), which originally related to the intrinsic characteristics that plants, animals, and other features of the world develop of their own accord. This is shown in the first written use of the word φύσις, in connection with a plant. The concept of nature as a whole, the physical universe, 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 in the last several centuries.

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 and geology of the Earth, and the matter and energy of which all these things are composed. It is often taken to mean the "natural environment" or wilderness - 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. This more traditional concept of natural things which can still be found today implies a distinction between the natural and the artificial, with the latter being understood as that which has been brought into being by a human or human-like consciousness or mind.

Earth

View of the home planet, taken in 1972 by the Apollo 17 crew. This image is the only photograph of its kind to date, showing a fully sunlit hemisphere of the Earth.^{[citation needed]}

Earth (or, "the earth") is the fifth largest planet in the solar system, third in order of distance from the Sun. It is the largest of its planetary system's terrestrial planets and the only place in the universe known to support life.

The most prominent features of the earth's climate are its two large polar regions, two relatively narrow temperate zones, and a wide equatorial tropical to subtropical region.^[6] Precipitation patterns vary widely according to location, ranging from several metres of water per year to less than a millimetre. About 70 percent of the surface is covered by salt-water oceans. The remainder consists of continents and islands, with the vast majority of the inhabited land in the Northern Hemisphere.

Earth has evolved through geological and biological processes that have left traces of the original conditions. The outer surface is divided into several tectonic plates that gradually migrate across the surface over geologic time spans, which at least several times have changed relatively quickly. The interior of the planet remains active, with a thick layer of molten Earth mantle and an iron-filled core that generates a magnetic field.

The atmospheric 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 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.

Historical perspective

Phylum Pediastrumboryanum. Plankton have been part of nature on the Earth for at least the past 2 billion years.

Based on the available evidence, scientists have reconstructed detailed information about the planet's past. Earth is estimated to have formed approximately 4.55 billion years ago out of the solar nebula, along with the Sun and other planets.^[12] The moon formed relatively soon afterwards (roughly 20 million years later, or 4.53 billion years ago).

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, augmented by ice delivered by comets, produced the oceans.^[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 re-formed as the surface of Earth reshaped itself over the course of 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.^[

Land-based plants and fungi have been part of nature on Earth for about the past 400 million years. These have needed to adapt and move many times as the continents and climates changed.

There is significant evidence, still being discussed among scientists, 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.^[18]

Since the Cambrian explosion there have been five distinctly identifiable mass extinctions.^[19] 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.

Several million years ago, a species of small African ape gained the ability to stand upright.^[21] 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.

 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.^[24] The extent of the current extinction event is still being researched, debated and calculated by biologists.

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...).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.

A supercell forming a thunderstorm with an associated strong updraft and a heavy precipitation of hail.

Terrestrial weather occurs almost exclusively in the lower part of the atmosphere, and serves as a convective system for redistributing heat. 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 dependent on its growth for their food.

The planetary climate is a measure of the long-term trends in the weather. 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. Overall, two things are currently happening worldwide: (1) temperature is increasing on the average; and (2) regional climates have been undergoing noticeable changes.^[28]

Life

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.^[29] Life may also be said to be simply the characteristic state of organisms.

Female mallard and ducklings - reproduction is essential for continuing life

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 air, land, surface rocks and water - within which life occurs, and which biotic processes in turn alter or transform. 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.^[30]

Over nine-tenths of the total biomass on Earth is plant life, on which animal life depends very heavily for its existence.^[31] More than 2 million species of plant and animal life have been identified to date,^[32] and estimates of the actual number of existing species range from several million to well over 50 million. 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. The total number of species is presently in rapid decline.

Life, as we understand it, is currently 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. 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 formation of ever-more diverse life forms.

Species that were unable to adapt to the changing environment and competition from other life forms became extinct. 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.

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. 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.^[42] 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.