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In software development, make is a utility for automatically building large applications. Files specifying instructions for make are called Makefiles. make is an expert system that tracks which files have changed since the last time the project was built and invokes the compiler on only those source code files and their dependencies. Before make's introduction, the Unix build system would most likely consist of "make" and "install" shell scripts accompanying a program's source. Being able to combine the commands for the different targets into a single file, and being able to abstract out dependency tracking and archive handling, was an important step in the direction of modern build environments. BSD make, which is derived from Adam de Boor's work on a version of make capable of building targets in parallel, and survives with varying degrees of modification in FreeBSD, NetBSD and OpenBSD. Most notably, it has conditionals and iterative loops which are applied at the parsing stage and may be used to conditionally, and programmatically, construct the makefile, including generation of targets at runtime. GNU make, which is part of most Linux installations and is frequently used in conjunction with the GNU build system. Its departures from traditional make are most noticeable in pattern-matching in dependency graphs and build targets, as well as a number of functions which may be invoked to have the make utility do things like collect a list of all files in the current directory. POSIX includes standardization of the basic features and operation of the make utility, and is implemented with varying degrees of completeness in Unix-based versions of make. In general, simple makefiles may be used between various versions of make with reasonable success. Some versions of GNU make and BSD make will look first for files named "GNUmakefile" and "BSDmakefile" respectively, which allows one to put makefiles which use implementation-defined behaviour in separate locations. In its basic form, Make requires the programmer to manually track all dependencies between files in the project. This process is error prone, since a forgotten or an extra dependency might not be immediately obvious, but instead surfaces as subtle bugs in the software. It is possible to create make files that generate some of these dependencies, but a more common solution is to use one of the available generators to make, e.g. Automake toolchain provided from the GNU Project. Another problem not well handled by make is the tailoring of a build process to a given platform. E.g, the compiler used on one platform might not accept the same options as the one used on another. This problem is typically handled by generating platform specific build instructions, which in turn are processed by make. Common tools for this process are Autoconf and Cmake. The syntax used by Make includes the use of tab, a whitespace character. Many editors do not provide very clear visual clues to the presence of tabs rather than spaces, and tab characters are not represented uniformly across editors in any case, with size varying from as little as 2 spaces to 8 spaces. Thus, the syntax of make is often subject to criticism. Some projects, such as Apache Ant, have attempted to redo make with a better syntax, with mixed success. For programmers using makefile generators, this issue is likely unimportant. With the advent of modern Integrated Development Environments, especially on non-Unix platforms, many programmers do not manually manage dependency tracking, or even the listing of which files are part of a project. Instead, the task is automated by the integrated environment. Likewise, many modern programming languages have language-specific ways of listing dependencies which are more efficiently tracked through the use of language-specific build utilities. These approaches typically have the drawback that support for arbitrary build instructions is limited. A makefile consists of lines of text which define a file (or set of files) or a rule name as depending on a set of files. Output files are marked as depending on their source files, for example, and source files are marked as depending on files which they include internally. After each dependency is listed, a series of lines of tab-indented text may follow which define how to transform the input into the output, if the former has been modified more recently than the latter. In the case where such definitions are present, they are referred to as "build scripts" and are passed to the shell to generate the target file. The basic structure is:[1] A makefile also can contain definitions of variables and inclusion of other makefiles. Variables in makefiles may be overridden in the command line arguments passed to the make utility. This allows users to specify different behaviour for the build scripts and how to invoke programs, among other things. For example, the variable "CC" is frequently used in makefiles to refer to a C compiler, and the user may wish to provide an alternate compiler to use.
A line can be described as an ideal zero-width, infinitely long, perfectly straight curve (the term curve in mathematics includes "straight curves") containing an infinite number of points. In Euclidean geometry, exactly one line can be found that passes through any two points. The line provides the shortest connection between the points. In two dimensions, two different lines can either be parallel, meaning they never meet, or may intersect at one and only one point. In three or more dimensions, lines may also be skew, meaning they don't meet, but also don't define a plane. Two distinct planes intersect in at most one line. Three or more points that lie on the same line are called collinear. This intuitive concept of a line can be formalized in various ways. If geometry is developed axiomatically (as in Euclid's Elements and later in David Hilbert's Foundations of Geometry), then lines are not defined at all, but characterized axiomatically by their properties. While Euclid did define a line as "length without breadth", he did not use this rather obscure definition in his later development. More abstractly, one usually thinks of the real line as the prototype of a line, and assumes that the points on a line stand in a one-to-one correspondence with the real numbers. However, one could also use the hyperreal numbers for this purpose, or even the long line of topology. In Euclidean geometry, a ray, or half-line, given two distinct points A (the origin) and B on the ray, is the set of points C on the line containing points A and B such that A is not strictly between C and B. In geometry, a ray starts at one point, then goes on forever in one direction.
Pit fired pottery is the oldest known method of firing clay-- and the ultimate source of all the modern firing variations used by potters. Unfired pots are nestled together in a pit in the ground and are then covered with burnable materials such as wood shavings, leaves, metal oxides, salts, sawdust and dried manure. The top of the pit may be protected with moist clay, shards, larger pieces of wood or metal baffles. The filled pit is then set on fire and carefully tended until most of the inner fuel has been consumed. The final pit temperature is generally low to moderate, approaching 2000 °F (1100 °C). This is in the range of temperatures used by ancient Native American potters or modern craftsmen producing earthenware. After cooling, pots are removed and cleaned to reveal dramatic patterns and colors left by ash and salt deposits. Pots may then be waxed and buffed to create a smooth glossy finish. Other traditional pottery processes which have been revived or modified by modern potters include the Asian technique of raku, the use of containers known as saggars in gas and wood fired kilns, and the use of salt as a glaze raw material.
Direct current (DC or "continuous current") is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through semiconductors, insulators, or even through a vacuum as in electron or ion beams. In direct current, the electric charges flow in the same direction, distinguishing it from alternating current (AC). A term formerly used for direct current was Galvanic current. Direct current may be obtained from an alternating current supply by use of a current-switching arrangement called a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be made into alternating current with an inverter or a motor-generator set. The first commercial electric power transmission (developed by Thomas Edison in the late nineteenth century) used direct current. Because of the advantage of alternating current over direct current in transforming and transmission, electric power distribution today is nearly all alternating current. For applications requiring direct current, such as third rail power systems, alternating current is distributed to a substation, which utilizes a rectifier to convert the power to direct current. See War of Currents. Direct current is used to charge batteries, and in nearly all electronic systems as the power supply. Very large quantities of direct-current power are used in production of aluminum and other electrochemical processes. Direct current is used for some railway propulsion, especially in urban areas. High voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids. Within electrical engineering, the term DC is a synonym for "constant". For example, the voltage across a DC voltage source is constant as is the current through a DC current source. The DC solution of an electric circuit is the solution where all voltages and currents are constant. It can be shown that any voltage or current waveform can be decomposed into a sum of a DC component and a time-varying component. The DC component is defined to be the average value of the voltage or current over all time. The average value of the time-varying component is zero. DC is commonly found in many low-voltage applications, especially where these are powered by batteries, which can produce only DC, or solar power systems, since solar cells can produce only DC. Most automotive applications use DC, although the alternator is an AC device which uses a rectifier to produce DC. Most electronic circuits require a DC power supply. Applications using fuel cells (mixing hydrogen and oxygen together with a catalyst to produce electricity and water as byproducts) also produce only DC. Most telephones connect to a twisted pair of wires, and internally separate the AC component of the voltage between the two wires (the audio signal) from the DC component of the voltage between the two wires (used to power the phone).
There is no definite boundary between the atmosphere and outer space. It slowly becomes thinner and fades into space. Three quarters of the atmosphere's mass is within 11 km of the planetary surface. In the United States, people who travel above an altitude of 80.5�km (50 statute miles) are designated astronauts. An altitude of 120�km (~75 miles or 400,000 ft) marks the boundary where atmospheric effects become noticeable during re-entry. The Kármán line, at 100�km (62 miles or 328,000 ft), is also frequently regarded as the boundary between atmosphere and outer space. Ionosphere: is the part of the atmosphere that is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth. It is located in the thermosphere and is responsible for auroras. Mesosphere: From the Greek word "μέσος" meaning middle. The mesosphere extends from about 50�km (160,000 ft) to the range of 80 to 85�km (265,000 – 285,000 ft), temperature decreasing with height. This is also where most meteors burn up when entering the atmosphere. Stratosphere: From the Latin word "stratus" meaning a spreading out. The stratosphere extends from the troposphere's 7 to 17�km (23,000 – 60,000 ft) range to about 50�km (160,000 ft). Temperature increases with height. The stratosphere contains the ozone layer, the part of the Earth's atmosphere which contains relatively high concentrations of ozone. "Relatively high" means a few parts per million—much higher than the concentrations in the lower atmosphere but still small compared to the main components of the atmosphere. It is mainly located in the lower portion of the stratosphere from approximately 15 to 35�km (50,000 – 115,000 ft) above Earth's surface, though the thickness varies seasonally and geographically. Troposphere: From the Greek word "τρέπω" meaning to turn or change. The troposphere is the lowest layer of the atmosphere; it begins at the surface and extends to between 7�km (23,000 ft) at the poles and 17�km (60,000 ft) at the equator, with some variation due to weather factors. The troposphere has a great deal of vertical mixing due to solar heating at the surface. This heating warms air masses, which makes them less dense so they rise. When an air mass rises the pressure upon it decreases so it expands, doing work against the opposing pressure of the surrounding air. To do work is to expend energy, so the temperature of the air mass decreases. As the temperature decreases, water vapor in the air mass may condense or solidify, releasing latent heat that further uplifts the air mass. This process determines the maximum rate of decline of temperature with height, called the adiabatic lapse rate. It contains roughly 80% of the total mass of the atmosphere. 50% of the total mass of the atmosphere is located in the lower 5 km of the troposphere. Atmospheric pressure is a direct result of the total weight of the air above the point at which the pressure is measured. This means that air pressure varies with location and time, because the amount (and weight) of air above the earth varies with location and time. Atmospheric pressure decreases with height, dropping by 50% at an altitude of about 5.6�km (18,000 ft). Equivalently, about 50% of the total atmospheric mass is within the lowest 5.6�km. This pressure drop is approximately exponential, so that pressure decreases by approximately half every 5.6�km. However, because of changes in temperature throughout the atmospheric column, as well as the fact that the force of gravity begins to decrease at great altitudes, a single equation does not model atmospheric pressure through all altitudes (it is modeled in 7 exponentially decreasing layers, in the equations given above). Below the turbopause at an altitude of about 100�km (not far from the mesopause), the Earth's atmosphere has a more-or-less uniform composition (apart from water vapor) as described above; this constitutes the homosphere.[5] However, above about 100�km, the Earth's atmosphere begins to have a composition which varies with altitude. This is essentially because, in the absence of mixing, the density of a gas falls off exponentially with increasing altitude, but at a rate which depends on the molar mass. Thus higher mass constituents, such as oxygen and nitrogen, fall off more quickly than lighter constituents such as helium, molecular hydrogen, and atomic hydrogen. Thus there is a layer, called the heterosphere, in which the earth's atmosphere has varying composition. As the altitude increases, the atmosphere is dominated successively by helium, molecular hydrogen, and atomic hydrogen. The precise altitude of the heterosphere and the layers it contains varies significantly with temperature. After loss of the hydrogen, helium and other hydrogen-containing gases from early Earth due to the Sun's radiation, primitive Earth was devoid of an atmosphere. The first atmosphere was formed by outgassing of gases trapped in the interior of the early Earth, which still goes on today in volcanoes. [6] The modern atmosphere is sometimes referred to as Earth's "third atmosphere", in order to distinguish the current chemical composition from two notably different previous compositions. The original atmosphere was primarily helium and hydrogen. Heat from the still-molten crust, and the sun, plus a probably enhanced solar wind, dissipated this atmosphere. About 4.4 billion years ago, the surface had cooled enough to form a crust, still heavily populated with volcanoes which released steam, carbon dioxide, and ammonia. This led to the early "second atmosphere", which was primarily carbon dioxide and water vapor, with some nitrogen but virtually no oxygen. This second atmosphere had approximately 100 times as much gas as the current atmosphere, but as it cooled much of the carbon dioxide was dissolved in the seas and precipitated out as carbonates. The later "second atmosphere" contained largely nitrogen and carbon dioxide. However, simulations run at the University of Waterloo and University of Colorado in 2005 suggest that it may have had up to 40% hydrogen.[7] It is generally believed that the greenhouse effect, caused by high levels of carbon dioxide and methane, kept the Earth from freezing. One of the earliest types of bacteria was the cyanobacteria. Fossil evidence indicates that bacteria shaped like these existed approximately 3.3 billion years ago and were the first oxygen-producing evolving phototropic organisms. They were responsible for the initial conversion of the earth's atmosphere from an anoxic state to an oxic state (that is, from a state without oxygen to a state with oxygen) during the period 2.7 to 2.2 billion years ago. Being the first to carry out oxygenic photosynthesis, they were able to produce oxygen while sequestering carbon dioxide in organic molecules, playing a major role in oxygenating the atmosphere. Photosynthesising plants would later evolve and continue releasing oxygen and sequestering carbon dioxide. Over time, excess carbon became locked in fossil fuels, sedimentary rocks (notably limestone), and animal shells. As oxygen was released, it reacted with ammonia to release nitrogen; in addition, bacteria would also convert ammonia into nitrogen. But most of the nitrogen currently present in the atmosphere results from sunlight-powered photolysis of ammonia released steadily over the aeons from volcanoes. As more plants appeared, the levels of oxygen increased significantly, while carbon dioxide levels dropped. At first the oxygen combined with various elements (such as iron), but eventually oxygen accumulated in the atmosphere, resulting in mass extinctions and further evolution. With the appearance of an ozone layer (ozone is an allotrope of oxygen) lifeforms were better protected from ultraviolet radiation. This oxygen-nitrogen atmosphere is the "third atmosphere". 200 – 250 million years ago, up to 35 percent of the atmosphere was oxygen (bubbles of ancient atmosphere were found in an amber). This modern atmosphere has a composition which is enforced by oceanic blue-green algae as well as geological processes. O2 does not remain naturally free in an atmosphere, but tends to be consumed (by inorganic chemical reactions, as well as by animals, bacteria, and even land plants at night), while CO2 tends to be produced by respiration and decomposition and oxidation of organic matter. Oxygen would vanish within a few million years due to chemical reactions and CO2 dissolves easily in water and would be gone in millennia if not replaced. Both are maintained by biological productivity and geological forces seemingly working hand-in-hand to maintain reasonably steady levels over millions of years (see Gaia theory). Air pollution is a chemical, physical (e.g. particulate matter) or biological agent that modifies the natural characteristics of the atmosphere in an unwanted way. Stratospheric ozone depletion due to air pollution (chiefly from chlorofluorocarbons) has long been recognized as a threat to human health as well as to the earth's ecosystems. Worldwide air pollution is responsible for large numbers of deaths and cases of respiratory disease. Enforced air quality standards, like the Clean Air Act in the United States, have reduced the presence of some pollutants. While major stationary sources are often identified with air pollution, the greatest source of emissions is actually mobile sources, principally the automobile. Gases such as carbon dioxide, methane, and fluorocarbons contribute to global warming, and these gases, or excess amounts of some emitted from fossil fuel burning, have recently been identified by the United States and many other countries (see Kyoto accord), as pollutants.
Software development, the utility is automatically perform for the large-scale building applications. Specify the procedure to file for a file called makeup. Making expert system, which tracks file has been changed since the last time the project is the integrated compiler simply call them the source code files and dependencies. Before the introduction of the UNIX system configuration to build the most expensive "make" and "install" shell script, attached to the program source. This combination can command for the different goals in a single file, and track dependencies can be abstract and handling the archives is an important step in the direction of modern building environment. BSD's, which is derived from the version ADAMUDOBOA build on the skills to work in parallel to the target building, in varying degrees of modification remaining, FreeBSD, NetBSD and OpenBSD. The most prominent, it is repetitive loops and conditions, will be applied at all stages of a conditional parsing, which may be used in the program and the construction of the Makefile, including targeting, runtime. GNU make, which is most of the parts are frequently used to install Linux and the GNU conjunction with the build system. Make a departure from the traditional pattern dependent on the most prominent target to build graphs, as well as a number of functions that may be invoked, how to do things like make utility of all files List collected in the current directory. POSIX standardization includes the basic features and operation of the make utility, and the full implementation of the varying degrees of UNIX-based version of make. In general, Makefiles easy it is to use reasonable between different versions of make success. Some versions of BSD and GNU make the file name in order to create the first to see "gnumakefile" and "bsdmakefile" respectively, which allows a single file to make use of different definitions implemented in place The behaviour. The basic form, the need to manually track programmers in the project all dependencies between files. This process, the error-prone, since extra dependencies or forgotten, it may be immediately obvious, instead of the subtle aspects of the software bug. Files can be created to generate these dependencies, but some of the more common solution is one of the available generators are used, for example, to automake toolchain GNU Project will be provided. Another problem is not well handled by the build process tailored to a given platform. For example, one of the platforms used in the same compiler options may not accept another used one. The problem is usually handled by the generation of specific steps for the platform will be processed in order. This process is a common tool for autoconf and cmake. This includes the use of syntax used tab and space characters. Not very clear on many editors to provide visual clues exist tab rather than space, and a tab character representation is not uniform across editors Anyhow, from the various dimensions of space and space just 2 8. Therefore, to make the syntax is often become a target of criticism. Some projects, such as Apache Ali, will try again tried to make a better syntax is a mixed success. Makefile for programmers using the generator, this problem is negligible. The advent of modern integrated development environment, especially for non-Unix platforms, many programmers do not have to manually manage dependency tracking, or any file for a listing of some projects. Instead, this task is the integration of the automation environment. Similarly, a modern programming language has many languages listed in a specific way, dependency tracking through the more efficient use of a specific language BIRUDOYUTIRITI. Typically, these approaches has drawbacks, and any steps to build support for the restrictions. Makefile define the configuration of a line of text (or a configuration file), depending on the set of rules or as a file name. Output files are marked as a source file, depending on, for example, the source file and the file is marked as, in response to internal included. Each dependency, after listing a number of lines of text tab indentation how to define it according to the input, output, has been updated, the more recent than the former, the latter. In these cases, the definitions exist, and they are called "Build script" is a shell passed from generation to the target file. The basic structure is: [1] The Makefile variables can be defined to include any other makeup inclusion. Makefiles will overwrite variables from the command line arguments passed to make utility. This allows the user to specify a variety of work, build scripts and learn how to run the program, among other things. For example, the variable "CC" is often used to refer to the file to make the C compiler, the user would like to offer using different compiler.
Line possibility, infinite long-term, is described took an ideal zero width completely straight curve (deadline curve in mathematics including "straight curve") contains a infinite numeral. In the European several reeds geometries, exactly were possibly discovered through an any two coarse thread. The line provides the shortest connection between the spot. In two dimensions, two different lines are possible perhaps parallel, meant they never meet, or perhaps intersects in which only has. Perhaps in three or more dimensions, the line and is twists, meant they do not meet, moreover does not define the airplane. A two distinct airplanes intersections at most coarse thread. Lies in with 样线three or more spots calls collinear. This line intuition concept possible formalization by various way. If geometry axiomatically is developed (later and in the Euclid element and in the David Hilbert geometry foundation), the line then is not defined, but is describes by theirs product axiomatically. When Euclid defined a coarse thread as the "length not to have breadth", he has not used this quite gloomy definition in his most recent development. More abstract, you usually thought the genuine line took the line the prototype, with the supposition, selects on-line stands in pair of correspondence by the real number. But, you can and use the hyperreal numeral for this goal, even topology long line. In the European several reeds geometries, the ray, or the beam, is given two clearly selects A (origin) and B in the ray, is the wrap selects C on-line to contain selects A and B like this, A strictly is not between C and B. In the geometry, the ray starts, forever however less advanced in a direction.
The china which is discharged by the pit the fire clay is oldest and all today the methodological potter who is known uses change of firing it is -- and final source. The pot of Unfired draws close together with the pit of the land, next wood product shavings and the leaf, metallic oxide, the salt and the sawdust and is covered with the burnable material like the fertilizer which is dried. Perhaps on the pit it is protected the clay and the fragment where the wood dampens, by the baffle of a larger part or metal. The pit which is filled up is placed with the fire then until the majority of the fuel inside was consumed, it is tend careful. Temperature of the final pit 2000 F gets near low generally in order to ease, (1100 C). As for this the potter of the ancient native American there is a range of the temperature which today the craftsman uses creates the earthenware. After the cooling, the pot is removed dramatic pattern and color in order to make the remainder clear by the deposit of the ash and the salt, becomes clean. Perhaps smooth can apply the pot and the wax in order to draw up the end which is glossy, polishes. Reviving, or being modified today by the potter include the furnace which is discharged as Asian technology and saggars of raku by the use and the wood of the container which is known with the gas other former china to process, and polish as raw materials use of the salt.
The current (DC or direct current ") is the flow of electric charge. Direct current is produced by sources such as batteries, thermocouples, solar cells, type collector and electrical machinery of the type dynamo. Direct current may flow in a conductor such as a wire, but it can also be done by semiconductors, insulators, or even through empty as beams of electrons or ions. In current, the flow of electrical charges in the same direction, distinguishing it from the alternating current (AC). A term used once for the galvanic current was common. In current can be obtained from an AC supply by the use of a switching device called a power rectifier, which contains electronic components (in general) or electromechanical components (historically), which allow current in only one direction. Direct current can be converted into alternating current with inverter or an engine-generator. The first electric power transmission business (developed by Thomas Edison in the late nineteenth century) used in common. Because of the advantage of AC to DC power, in addition to the processing and transmission, power distribution is now almost all of alternating current. For applications requiring a continuous flow, as the third rail power systems, alternating current is distributed to a post, which uses a rectifier to convert the DC power. See War currents. Direct current is used to charge batteries, and in almost all electronic systems as electricity. Very large quantities of direct-current power are used in the production of aluminum and other electrochemical processes. Direct current is used to propel rail, particularly in urban areas. High voltage direct current is used to transmit large amounts of energy generation from remote sites or at the interconnection of electric power AC. As part of the electrical engineering, the DC term is a synonym for "constant". For example, the voltage across a DC voltage source is constant as is currently the case through a DC current source. The solution to a DC electrical system is the solution when all the voltages and currents are constant. It can be shown that any form of current or voltage can be decomposed into a sum of a DC component and a variable component in time. The DC component is defined as the average value of the voltage or current of all time. The average value of time-varying component is zero. DC is commonly found in many low-voltage applications, especially when they are powered by batteries, which can only happen DC, or solar collectors, as solar cells can produce only DC. Most applications use the automobile DC, although AC generator is a device that uses a DC rectifier to produce. Most electronic circuits require a DC power supply. Applications using fuel cells (a mixture of hydrogen and oxygen with a catalyst to produce electricity and water as byproducts) that produce DC. Most phones connect to a twisted pair of wires, and separate component of the AC voltage between the two wires (the audio signal) of the DC component of the tension between the two wires (used to power the phone).
There is no clear boundary between the atmosphere and space. It is thinner and slowly fades into space. Three-quarters of the atmosphere inside the ground is 11 km from the planetary surface. In the United States, people who travel in a height of 80.5 km (50 statute miles) are astronauts. One altitude of 120 km (75 miles or 400000 ~ m) marks the border, where atmospheric effects will be felt during re-entry. The Kármán-line at 100 km (62 miles or 328000 m), is also often used as the boundary between the atmosphere and space. Ionosphere: is the part of the atmosphere caused by solar radiation ionized. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. He has practical significance because among other functions, it affects the radio propagation to distant places on Earth. It is located in the Thermo sphere, and is responsible for the Earth's magnetosphere. Mesosphere: From the Greek word "μέσος" means middle. The mesosphere ranges from about 50 km (160000 m), in the range of 80 to 85 km (265000 - 285000 m), the temperature decreases with altitude. This is also where most meteors burn when in the atmosphere. Stratosphere: From the Latin word "Stratus", ie spreading. The stratosphere extends from the troposphere is between 7 and 17 km (23000 - 60000 ft) range of up to 50 km (160000 ft). Temperature increases with the altitude. The stratosphere contains the ozone layer, the part of the earth's atmosphere contains relatively high concentrations of ozone. "Relatively high" means a few parts per million, much higher than the concentration in the lower atmosphere, but still small in comparison to the major components of the atmosphere. It is especially in the lower part of the stratosphere about 15 to 35 km (50000 - 115000 ft) above the Earth's surface, if the thickness varies seasonally and geographically. Troposphere: From the Greek word "τρέπω" meaning to turn or change. The troposphere is the lowest layer of the atmosphere, it starts at the surface and extends between 7 km (23000 m) at the poles and 17 km (60000 m) at the equator, with some deviations due to weather factors. The troposphere is a large vertical mixing by solar heat at the surface. This heater warms air masses, making it less dense, so that they grow. If an air mass is increasing the pressure on them is so extended, work against the opposing pressure of the surrounding air. Work to be done to expend energy, so that the temperature of the air mass decreases. As the temperature drops, water vapor in the air or ground can consolidate, release of latent heat that further surcharges air mass. This process determines the maximum rate of decrease in temperature with altitude, the so-called adiabatic lapse. It contains approximately 80% of the total mass of the atmosphere. 50% of the total mass of the atmosphere is in the lower 5 km from the troposphere. The atmospheric pressure is a direct result of the total weight of the air above the point at which the pressure is measured. This means that the air pressure varies by place and time, because the amount (weight) of air above the Earth depends on the place and time. The atmospheric pressure increases with altitude, decreasing from 50% at an altitude of about 5.6 km (18000 ft). Equivalent, about 50% of the total mass of the atmosphere is in the lowest 5.6 km. This pressure drop is approximately exponentially, so that the pressure is reduced by about half of all 5.6 km. Because of the changes in the temperature of the atmosphere in the entire column, as well as the fact that gravity starts to fall in large amounts, not a single equation model atmospheric pressure through all the heights (it is modeled in 7 layers exponentially decreasing, in the equations above). Below the turbopause at an altitude of about 100 km (not far from the mesopause), the Earth's atmosphere has a more or less uniform composition (apart from water vapor), as described above, is the homosphere. [5] However, more than 100 km, the Earth's atmosphere begins the composition varies with the altitude. This is primarily because, in the absence of mixing, the density of a gas from falls exponentially with increasing altitude, but at a rate that depends on the molecular weight. So higher mass elements such as oxygen and nitrogen fall faster than lighter elements, such as helium, hydrogen molecular and atomic hydrogen. Therefore, there is a layer, the so-called heterosphere, where the atmosphere is different composition. As the height increases, the atmosphere is characterized by the gradual helium, molecular hydrogen and atomic hydrogen. The exact amount of heterosphere and its layers varies greatly with the temperature. After the loss of hydrogen, helium and other hydrogen-containing gases, from the early earth by the radiation of the sun, primitive Earth was devoid of an atmosphere. The first atmosphere created by outgassing of the gases in the interior of the early earth, which still goes on today in volcanoes. [6] The modern atmosphere is sometimes referred to as "Earth" third atmosphere "to the current chemical composition mainly from two different previous compositions. Original atmosphere was primarily hydrogen and helium. Heat from the molten crust yet, and the sun, and probably a stronger solar wind, broke up this atmosphere. About 4.4 billion years ago, the surface had cooled enough for a crust that are still heavily populated with volcanoes, the released vapor, carbon dioxide and ammonia. This led to the At the beginning of the "second" atmosphere, primarily carbon dioxide and water vapor, with some, but virtually no nitrogen-oxygen. This second atmosphere had about 100 times as much gas as the current atmosphere, but as it cooled much of the carbon dioxide was dissolved in the oceans as carbonate precipitated. later, "second atmosphere" largely contained nitrogen and carbon dioxide. however, simulations run at the University of Waterloo and the University of Colorado in 2005 suggests that it may have had up to 40 % hydrogen. [7] It is generally considered that the greenhouse effect, caused by a high level of carbon dioxide and methane, kept the soil from freezing. one of the earliest species of bacteria was the cyanobacteria. fossil suggests that these bacteria existed in the form of approximately 3.3 billion years ago and were the first oxygen-producing phototropic evolving organisms. they were responsible for the initial conversion of the Earth's atmosphere from an anoxic oxic state to a state (that is, from a state without oxygen to a State with oxygen) in the period from 2.7 to 2.2 billion years ago. Firstly, to carry out oxygenic photosynthesis, they were able to produce oxygen, while sequestering carbon dioxide into organic molecules play an important role in the atmosphere oxygenating. photosynthesis capacity plant would later develop and continue the release of oxygen and carbon dioxide sequestration. Over time was locked excess carbon in fossil fuels, sedimentary rocks (especially lime stone), mussels and animals. Since oxygen was released, it reacts with ammonia to release nitrogen; also would even bacteria convert ammonia into nitrogen. But most of the nitrogen present in the atmosphere, it is clear from sunlight-powered photolysis of ammonia released steadily over the aeons of volcanoes. As more plants appeared, the levels of oxygen increased significantly, while the carbon dioxide levels decreased. At first oxygen in connection with various elements (such as iron), but also oxygen in the atmosphere, leading to mass death and further development. with the appearance of an ozone layer (Ozone is an allotrope of oxygen) forms of life were better before UV radiation. this oxygen-nitrogen atmosphere is the "third atmosphere." 200 to 250 million years ago, up to 35 percent of the atmosphere was oxygen (bubbles of ancient atmosphere were in a Bernstein). this modern atmosphere has a composition, compliance with the oceanic blue-green algae, and geological processes. O2 not stay course in a free atmosphere, but more likely to be consumed (by inorganic chemical reactions, as well as animals, bacteria, plants and even country in the night), while the CO2 ousted by respiration and decomposition and oxidation of organic matter. Oxygen would disappear within a few million years ago by chemical reactions and CO2 dissolves easily in water and would have gone in, if not millennia replaced. both operated by the biological productivity and geological forces seemingly working hand in hand to secure reasonably steady level over millions of years (see Gaia theory). air pollution is a chemical, physical (eg particle), or biological agents, will change the natural properties of the atmosphere in an undesirable way. reduction of the ozone layer in the stratosphere by air pollution (mainly from chlorofluorocarbons substances) has long been considered a threat to human health and ecosystems of the earth. world-wide air pollution is responsible for the large number of deaths and cases of respiratory diseases. air quality standards are enforced , as the Clean Air Act in the United States, the presence of some pollutants. While the major stationary sources are often associated with air pollution, the largest source of emissions is actually mobile sources, mainly in the automotive industry. gases such as carbon dioxide, methane, hydrofluorocarbons, and contribute to global warming, and these gases or excess amounts of some emitted from fossil-fuel burning, were recently by the United States and many other countries (see Kyoto agreement), as pollutants.
