Video game genre
A video game genre is a classification assigned to a video game based on its gameplay interaction rather than visual or narrative differences. A video game genre is defined by a set of gameplay challenges and are classified independently of their setting or game-world content, unlike other works of fiction such as films or books. For example, a shooter game is still a shooter game, regardless of when it takes place; as with nearly all varieties of genre classification, the matter of any individual video game's specific genre is open to personal interpretation. Moreover, each individual game may belong to several genres at once; the first attempt to classify different genres of video games was made by Chris Crawford in his book The Art of Computer Game Design in 1984. In this book, Crawford focused on the player's experience and activities required for gameplay. Here, he stated that "the state of computer game design is changing quickly. We would therefore expect the taxonomy presented to become obsolete or inadequate in a short time."
Since among other genres, the platformer and 3D shooter genres, which hardly existed at the time, have gained a lot of popularity. As hardware capabilities have increased, new genres have become possible, with examples being increased memory, the move from 2D to 3D, new peripherals and location. Though genres were just interesting for game studies in the 1980s, the business of video games expanded in the 1990s and both smaller and independent publishers had little chance of surviving; because of this, games settled more into set genres that larger publishers and retailers could use for marketing. Due to "direct and active participation" of the player, video game genres differ from literary and film genres. Though one could state that Space Invaders is a science-fiction video game, such a classification "ignores the differences and similarities which are to be found in the player's experience of the game." In contrast to the visual aesthetics of games, which can vary it is argued that it is interactivity characteristics that are common to all games.
Descriptive names of genres take into account the goals of the game, the protagonist and the perspective offered to the player. For example, a first-person shooter is a game, played from a first-person perspective and involves the practice of shooting; the term "subgenre" may be used to refer to a category within a genre to further specify the genre of the game under discussion. Whereas "shooter game" is a genre name, "first-person shooter" and "third-person shooter" are common subgenres of the shooter genre. Other examples of such prefixes are real-time, turn based, side-scrolling; the target audience, underlying theme or purpose of a game are sometimes used as a genre identifier, such as with "games for girls," games for cats,"Christian game" and "Serious game" respectively. However, because these terms do not indicate anything about the gameplay of a video game, these are not considered genres. Video game genres vary in specificity, with popular video game reviews using genre names varying from "action" to "baseball."
In this practice, basic themes and more fundamental characteristics are used alongside each other. A game may combine aspects of multiple genres in such a way that it becomes hard to classify under existing genres. For example, because Grand Theft Auto III combined shooting and roleplaying in an unusual way, it was hard to classify using existing terms. Since the term Grand Theft Auto clone has been used to describe games mechanically similar to Grand Theft Auto III; the term roguelike has been developed for games that share similarities with Rogue. Elements of the role-playing genre, which focuses on storytelling and character growth, have been implemented in many different genres of video games; this is because the addition of a story and character enhancement to an action, strategy or puzzle video game does not take away from its core gameplay, but adds an incentive other than survival to the experience. According to some analysts, the count of each broad genre in the best selling physical games worldwide is broken down as follows.
The most popular genres are Shooter, Role-playing and Sports, with Platformer and Racing having both declined in the last decade. Puzzle games have declined when measured by sales, however, on mobile, where the majority of games are free-to-play, this genre remains the most popular worldwide. List of video game genres
MS-DOS is an operating system for x86-based personal computers developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, some operating systems attempting to be compatible with MS-DOS, are sometimes referred to as "DOS". MS-DOS was the main operating system for IBM PC compatible personal computers during the 1980s and the early 1990s, when it was superseded by operating systems offering a graphical user interface, in various generations of the graphical Microsoft Windows operating system. MS-DOS was the result of the language developed in the seventies, used by IBM for its mainframe operating system. Microsoft acquired the rights to meet IBM specifications. IBM re-released it on August 12, 1981 as PC DOS 1.0 for use in their PCs. Although MS-DOS and PC DOS were developed in parallel by Microsoft and IBM, the two products diverged after twelve years, in 1993, with recognizable differences in compatibility and capabilities. During its lifetime, several competing products were released for the x86 platform, MS-DOS went through eight versions, until development ceased in 2000.
MS-DOS was targeted at Intel 8086 processors running on computer hardware using floppy disks to store and access not only the operating system, but application software and user data as well. Progressive version releases delivered support for other mass storage media in greater sizes and formats, along with added feature support for newer processors and evolving computer architectures, it was the key product in Microsoft's growth from a programming language company to a diverse software development firm, providing the company with essential revenue and marketing resources. It was the underlying basic operating system on which early versions of Windows ran as a GUI, it is a flexible operating system, consumes negligible installation space. MS-DOS was a renamed form of 86-DOS – owned by Seattle Computer Products, written by Tim Paterson. Development of 86-DOS took only six weeks, as it was a clone of Digital Research's CP/M, ported to run on 8086 processors and with two notable differences compared to CP/M.
This first version was shipped in August 1980. Microsoft, which needed an operating system for the IBM Personal Computer hired Tim Paterson in May 1981 and bought 86-DOS 1.10 for $75,000 in July of the same year. Microsoft kept the version number, but renamed it MS-DOS, they licensed MS-DOS 1.10/1.14 to IBM, who, in August 1981, offered it as PC DOS 1.0 as one of three operating systems for the IBM 5150, or the IBM PC. Within a year Microsoft licensed MS-DOS to over 70 other companies, it was designed to be an OS. Each computer would have its own distinct hardware and its own version of MS-DOS, similar to the situation that existed for CP/M, with MS-DOS emulating the same solution as CP/M to adapt for different hardware platforms. To this end, MS-DOS was designed with a modular structure with internal device drivers, minimally for primary disk drives and the console, integrated with the kernel and loaded by the boot loader, installable device drivers for other devices loaded and integrated at boot time.
The OEM would use a development kit provided by Microsoft to build a version of MS-DOS with their basic I/O drivers and a standard Microsoft kernel, which they would supply on disk to end users along with the hardware. Thus, there were many different versions of "MS-DOS" for different hardware, there is a major distinction between an IBM-compatible machine and an MS-DOS machine; some machines, like the Tandy 2000, were MS-DOS compatible but not IBM-compatible, so they could run software written for MS-DOS without dependence on the peripheral hardware of the IBM PC architecture. This design would have worked well for compatibility, if application programs had only used MS-DOS services to perform device I/O, indeed the same design philosophy is embodied in Windows NT. However, in MS-DOS's early days, the greater speed attainable by programs through direct control of hardware was of particular importance for games, which pushed the limits of their contemporary hardware. Soon an IBM-compatible architecture became the goal, before long all 8086-family computers emulated IBM's hardware, only a single version of MS-DOS for a fixed hardware platform was needed for the market.
This version is the version of MS-DOS, discussed here, as the dozens of other OEM versions of "MS-DOS" were only relevant to the systems they were designed for, in any case were similar in function and capability to some standard version for the IBM PC—often the same-numbered version, but not always, since some OEMs used their own proprietary version numbering schemes —with a few notable exceptions. Microsoft omitted multi-user support from MS-DOS because Microsoft's Unix-based operating system, was multi-user; the company planned, over time, to improve MS-DOS so it would be indistinguishable from single-user Xenix, or XEDOS, which would run on the Motorola 68000, Zilog Z8000, the LSI-11. Microsoft advertised MS-DOS and Xenix together, listing the shared features of its "single-user OS" and "the multi-user, multi-tasking, UNIX-derived operating system", promising easy
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English, Mars carries a name of the Roman god of war, is referred to as the "Red Planet" because the reddish iron oxide prevalent on its surface gives it a reddish appearance, distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys and polar ice caps of Earth; the days and seasons are comparable to those of Earth, because the rotational period as well as the tilt of the rotational axis relative to the ecliptic plane are similar. Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, of Valles Marineris, one of the largest canyons in the Solar System; the smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons and Deimos, which are small and irregularly shaped.
These may be captured asteroids, similar to a Mars trojan. There are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers. Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, less than 1% of the Earth's, except at the lowest elevations for short periods; the two polar ice caps appear to be made of water. The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters. In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars; the volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior. Mars can be seen from Earth with the naked eye, as can its reddish coloring, its apparent magnitude reaches −2.94, surpassed only by Jupiter, the Moon, the Sun.
Optical ground-based telescopes are limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earth's atmosphere. Mars is half the diameter of Earth with a surface area only less than the total area of Earth's dry land. Mars is less dense than Earth, having about 15% of Earth's volume and 11% of Earth's mass, resulting in about 38% of Earth's surface gravity; the red-orange appearance of the Martian surface is caused by rust. It can look like butterscotch. Like Earth, Mars has differentiated into a dense metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ± 65 kilometers, consisting of iron and nickel with about 16–17% sulfur; this iron sulfide core is thought to be twice as rich in lighter elements as Earth's. The core is surrounded by a silicate mantle that formed many of the tectonic and volcanic features on the planet, but it appears to be dormant. Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, aluminum and potassium.
The average thickness of the planet's crust is about 50 km, with a maximum thickness of 125 km. Earth's crust averages 40 km. Mars is a terrestrial planet that consists of minerals containing silicon and oxygen and other elements that make up rock; the surface of Mars is composed of tholeiitic basalt, although parts are more silica-rich than typical basalt and may be similar to andesitic rocks on Earth or silica glass. Regions of low albedo suggest concentrations of plagioclase feldspar, with northern low albedo regions displaying higher than normal concentrations of sheet silicates and high-silicon glass. Parts of the southern highlands include detectable amounts of high-calcium pyroxenes. Localized concentrations of hematite and olivine have been found. Much of the surface is covered by finely grained iron oxide dust. Although Mars has no evidence of a structured global magnetic field, observations show that parts of the planet's crust have been magnetized, suggesting that alternating polarity reversals of its dipole field have occurred in the past.
This paleomagnetism of magnetically susceptible minerals is similar to the alternating bands found on Earth's ocean floors. One theory, published in 1999 and re-examined in October 2005, is that these bands suggest plate tectonic activity on Mars four billion years ago, before the planetary dynamo ceased to function and the planet's magnetic field faded, it is thought that, during the Solar System's formation, Mars was created as the result of a stochastic process of run-away accretion of material from the protoplanetary disk that orbited the Sun. Mars has many distinctive chemical features caused by its position in the Solar System. Elements with comparatively low boiling points, such as chlorine and sulphur, are much more common on Mars than Earth. After the formation of the planets, all were subjected to the so-called "Late Heavy Bombardment". About 60% of the surface of Mars shows a record of impacts from that era, whereas much of the remaining surface is underlain by immense impact basins caused by those events.
There is evidence of an enormous impact basin in the northern hemisphere of Mars, spanning 10,600 by 8,500 km, or four times the size of the Moon's South Pole – Aitk
A Martian is a native inhabitant of the planet Mars. Although the search for evidence of life on Mars continues, many science fiction writers have imagined what extraterrestrial life on Mars might be like; some writers use the word Martian to describe a human colonist on Mars. The earliest known instances of the word "Martian", used as a noun instead of an adjective, were printed in late 1877, they appeared nearly in England and the United States, in magazine articles detailing Asaph Hall's discovery of the moons of Mars in August of that year. The next event to inspire the use of the noun Martian in print was the International Exposition of Electricity, hosted in Paris in the year 1881. During the four months of the exhibition, many people visited to witness such technological marvels as the incandescent light bulb and the telephone. One visitor came away wondering what kind of world such innovations might engender in the next 200 years. Writing anonymously, s/he assembled some speculations in an essay titled "The Year of Grace 2081", which enjoyed wide circulation.
The Martians enter the story late in the narrative. During a rest from international conflict on Earth, humans begin telecommunicating with Martians. "After a brief period passed in the exchange of polite messages", says the essayist, humans will decide to war with the Martians on some pretence of honor. The war that results is cataclysmic: will unite all their energies for the fabrication of mammoth engines which will discharge oceans of water and fire right into the face of Mars. In return, the Martians will pelt them with aeroliths weighing three thousand tons, which will chip whole mountains off the Himalayas and make a big hole where Mont Blanc now exists. W. S. Lach-Szyrma's novel Aleriel, or A Voyage to Other Worlds was reputed to be the first published work to apply the word Martian as a noun; the usage is incidental. Aleriel buries the car in snow "so that it might not be disturbed by any Martian who might come across it." Fifteen years after Aleriel, H. G. Wells' landmark novel The War of the Worlds was published by William Heinemann, Ltd. a new publishing house.
The novel was revised numerous times, has since been translated into many languages. In the story, the Martians are a technologically advanced race of octopus-like extraterrestrials who invade Earth because Mars is becoming too cold to sustain them; the Martians' undoing is a fatal vulnerability to Earth bacteria. In his book Mars and Its Canals and businessman Percival Lowell conjectured that an extinct Martian race had once constructed a vast network of aqueducts to channel water to their settlements from Mars' polar ice caps, Planum Australe and Planum Boreum. Lowell did not invent this Martian canal hypothesis; the belief that Mars had canals was based on observations Giovanni Schiaparelli made through his reflecting telescope. Although the telescope's image was fuzzy, Schiaparelli thought he saw long, straight lines on the Martian surface; this idea inspired Lowell, who returned to the subject in Mars As the Abode of Life, in which he wrote a fanciful description of what this Martian society may have been like.
Although his description was based on no evidence, Lowell's words evoked vivid pictures in his readers' imaginations. One of the people Lowell inspired was Edgar Rice Burroughs, who began writing his own story about Mars in the summer of 1911; the story is a planetary romance in which an American Civil War veteran named John Carter is transported to Mars when he walks inside a cave on Earth. He finds that Mars is populated by two species of warring humanoids, he becomes embroiled in their conflict. In February 1912, an American pulp magazine called The All-Story published Burroughs' story as the first installment of a serial novel, which the editor titled Under the Moons of Mars; the book was the first in Burroughs' Barsoom series. Although the noun Martian can describe any organism from Mars and works imagine Martians as a humanoid monoculture. Martian, in this sense, is more like the word human than the word Earthling. In science fiction, Martians are stereotypically imagined in one or more of the following ways: as alien invaders.
H. G. Wells' novel The War of the Worlds and its various adaptations have been an extraordinary influence on science fiction writers for more than 100 years. Wells' Martians are a technologically advanced species with an ancient civilization, they somewhat resemble cephalopods, with large, bulky brown bodies and sixteen snake-like tentacles, in two groups of eight, around a quivering V-shaped mouth. They invade Earth because Mars is dying, they need a warmer planet to live, they attack cities in southern England, including London, with a deadly heat-ray they fire from a camera-like device on an articulated arm attached to their tripods. Mankind is saved by Earth bacteria, which
In demographics, the world population is the total number of humans living, was estimated to have reached 7.6 billion people as of May 2018. It took over 200,000 years of human history for the world's population to reach 1 billion. World population has experienced continuous growth since the end of the Great Famine of 1315–1317 and the Black Death in 1350, when it was near 370 million; the highest population growth rates – global population increases above 1.8% per year – occurred between 1955 and 1975, peaking to 2.06% between 1965 and 1970. The growth rate has declined to 1.18% between 2010 and 2015 and is projected to decline further in the course of the 21st century. However, the global population is still growing and is projected to reach about 10 billion in 2050 and more than 11 billion in 2100. Total annual births were highest in the late 1980s at about 139 million, as of 2011 were expected to remain constant at a level of 135 million, while deaths numbered 56 million per year and were expected to increase to 80 million per year by 2040.
The median age of the world's population was estimated to be 30.4 years in 2018. Six of the Earth's seven continents are permanently inhabited on a large scale. Asia is the most populous continent, with its 4.54 billion inhabitants accounting for 60% of the world population. The world's two most populated countries and India, together constitute about 36% of the world's population. Africa is the second most populated continent, with around 1.28 billion people, or 16% of the world's population. Europe's 742 million people make up 10% of the world's population as of 2018, while the Latin American and Caribbean regions are home to around 651 million. Northern America consisting of the United States and Canada, has a population of around 363 million, Oceania, the least populated region, has about 41 million inhabitants. Though it is not permanently inhabited by any fixed population, Antarctica has a small, fluctuating international population based in polar science stations; this population tends to rise in the summer months and decrease in winter, as visiting researchers return to their home countries.
Estimates of world population by their nature are an aspect of modernity, possible only since the Age of Discovery. Early estimates for the population of the world date to the 17th century: William Petty in 1682 estimated world population at 320 million. More refined estimates, broken down by continents, were published in the first half of the 19th century, at 600 to 1000 million in the early 1800s and at 800 to 1000 million in the 1840s, it is difficult for estimates to be better than rough approximations, as modern population estimates are fraught with uncertainties on the order of 3% to 5%. Estimates of the population of the world at the time agriculture emerged in around 10,000 BC have ranged between 1 million and 15 million. Earlier, genetic evidence suggests humans may have gone through a population bottleneck of between 1,000 and 10,000 people about 70,000 BC, according to the Toba catastrophe theory. By contrast, it is estimated that around 50–60 million people lived in the combined eastern and western Roman Empire in the 4th century AD.
The Plague of Justinian, which first emerged during the reign of the Roman emperor Justinian, caused Europe's population to drop by around 50% between the 6th and 8th centuries AD. The population of Europe was more than 70 million in 1340; the Black Death pandemic of the 14th century may have reduced the world's population from an estimated 450 million in 1340 to between 350 and 375 million in 1400. The population of China decreased from 123 million in 1200 to 65 million in 1393 due to a combination of Mongol invasions and plague. Starting in AD 2, the Han Dynasty of ancient China kept consistent family registers in order to properly assess the poll taxes and labor service duties of each household. In that year, the population of Western Han was recorded as 57,671,400 individuals in 12,366,470 households, decreasing to 47,566,772 individuals in 9,348,227 households by AD 146, towards the End of the Han Dynasty. At the founding of the Ming Dynasty in 1368, China's population was reported to be close to 60 million.
England's population reached an estimated 5.6 million in 1650, up from an estimated 2.6 million in 1500. New crops that were brought to Asia and Europe from the Americas by Portuguese and Spanish colonists in the 16th century are believed to have contributed to population growth. Since their introduction to Africa by Portuguese traders in the 16th century and cassava have replaced traditional African crops as the most important staple food crops grown on the continent; the pre-Columbian North American population numbered somewhere between 2 million and 18 million. Encounters between European explorers and populations in the rest of the world introduced local epidemics of extraordinary virulence. According to the most extreme scholarly claims, as many as 90% of the Native American population of the New World died due to Old World diseases such as smallpox and influenza. Over the centuries, the Europeans had developed high degrees of immunity to these diseases, while the indigenous peoples had no such immunity.
During the European Agricultural and Industrial Revolutions, the life expectancy of children increased dramatically. The percentage of the children born in London who died before the age of five decreased from 74.5% in
Terraforming or terraformation of a planet, moon, or other body is the hypothetical process of deliberately modifying its atmosphere, surface topography or ecology to be similar to the environment of Earth to make it habitable by Earth-like life. The concept of terraforming developed from actual science; the term was coined by Jack Williamson in a science-fiction short story published during 1942 in Astounding Science Fiction, but the concept may pre-date this work. If the environment of a planet could be altered deliberately, the feasibility of creating an unconstrained planetary environment that mimics Earth on another planet has yet to be verified. Mars is considered to be the most candidate for terraforming. Much study has been done concerning the possibility of heating the planet and altering its atmosphere, NASA has hosted debates on the subject. Several potential methods of altering the climate of Mars may fall within humanity's technological capabilities, but at present the economic resources required to do so are far beyond that which any government or society is willing to allocate to it.
The long timescales and practicality of terraforming are the subject of debate. Other unanswered questions relate to the ethics, economics and methodology of altering the environment of an extraterrestrial world; the renowned astronomer Carl Sagan proposed the planetary engineering of Venus in an article published in the journal Science in 1961. Sagan imagined seeding the atmosphere of Venus with algae, which would convert water and carbon dioxide into organic compounds; as this process removed carbon dioxide from the atmosphere, the greenhouse effect would be reduced until surface temperatures dropped to "comfortable" levels. The resulting carbon, Sagan supposed, would be incinerated by the high surface temperatures of Venus, thus be sequestered in the form of "graphite or some involatile form of carbon" on the planet's surface; however discoveries about the conditions on Venus made this particular approach impossible. One problem is that the clouds of Venus are composed of a concentrated sulfuric acid solution.
If atmospheric algae could thrive in the hostile environment of Venus's upper atmosphere, an more insurmountable problem is that its atmosphere is far too thick—the high atmospheric pressure would result in an "atmosphere of nearly pure molecular oxygen" and cause the planet's surface to be thickly covered in fine graphite powder. This volatile combination could not be sustained through time. Any carbon, fixed in organic form would be liberated as carbon dioxide again through combustion, "short-circuiting" the terraforming process. Sagan visualized making Mars habitable for human life in "Planetary Engineering on Mars", an article published in the journal Icarus. Three years NASA addressed the issue of planetary engineering in a study, but used the term "planetary ecosynthesis" instead; the study concluded that it was possible for Mars to support life and be made into a habitable planet. The first conference session on terraforming referred to as "Planetary Modeling", was organized that same year.
In March 1979, NASA engineer and author James Oberg organized the First Terraforming Colloquium, a special session at the Lunar and Planetary Science Conference in Houston. Oberg popularized the terraforming concepts discussed at the colloquium to the general public in his book New Earths. Not until 1982 was the word terraforming used in the title of a published journal article. Planetologist Christopher McKay wrote "Terraforming Mars", a paper for the Journal of the British Interplanetary Society; the paper discussed the prospects of a self-regulating Martian biosphere, McKay's use of the word has since become the preferred term. In 1984, James Lovelock and Michael Allaby published The Greening of Mars. Lovelock's book was one of the first to describe a novel method of warming Mars, where chlorofluorocarbons are added to the atmosphere. Motivated by Lovelock's book, biophysicist Robert Haynes worked behind the scenes to promote terraforming, contributed the neologism Ecopoiesis, forming the word from the Greek οἶκος, oikos, "house", ποίησις, poiesis, "production".
Ecopoiesis refers to the origin of an ecosystem. In the context of space exploration, Haynes describes ecopoiesis as the "fabrication of a sustainable ecosystem on a lifeless, sterile planet". Fogg defines ecopoiesis as a type of planetary engineering and is one of the first stages of terraformation; this primary stage of ecosystem creation is restricted to the initial seeding of microbial life. As conditions approach that of Earth, plant life could be brought in, this will accelerate the production of oxygen, theoretically making the planet able to support animal life. Beginning in 1985, Martyn J. Fogg started publishing several articles on terraforming, he served as editor for a full issue on terraforming for the Journal of the British Interplanetary Society in 1992. In his book Terraforming: Engineering Planetary Environments, Fogg proposed the following definitions for different aspects related to terraforming: Planetary engineering: the application of technology for the purpose of influencing the global properties of a planet.
Geoengineering: planetary engineering applied to Earth. It includes only those macroengineering concepts that deal with the alteration of some global parameter, such as the greenhouse effect, atmospheric composition, insolation or impact flux. Terraforming: a process of planetary engineering directed at enhancing the capacity of an extraterrestrial planetary environment to support li