Terraform



"Fry: I'm impressed. In my time we had no idea Mars had a university.

Professor Farnsworth: That's because then Mars was a uninhabitable wasteland, much like Utah. But unlike Utah, Mars was eventually made livable when the university was founded in 2636.

Leela: They planted traditional college foliage. Ivy... trees... hemp... soon the whole planet was terraformed!"

- Futurama, Mars University

A Speculative Fiction staple, the act of turning an otherwise human-unfriendly environment into an Earth-like, or "Terra-formed" planet. Narratively, this is done to give the cast a place to go outside the ship (off Earth) that won't require them dressing in Space Clothes constantly. Within a given setting, it's often done to showcase humanity's drive to explore and colonize new places for the famed trifecta of God, Gold and Glory. (Hey, at least one setting actively proselytizes, at gunpoint!)

Often used to explain why All Planets Are Earthlike.

Terraforming itself is an actual area of study right now, as scientists try to design methods to create both self-contained environments (Bio-Domes being famous examples) and species that can survive in a hostile environment and improve it until it has a self-sustaining biosphere that can sustain humans. Easier said than done. Literally, because soft sci-fi settings tend to sneeze out terraforming efforts and planets like Martians with a cold.

Harder scifi settings can construct entire books about the sciences and engineering involved, not to mention the political and social effort these huge undertakings would entail.

We would also like to draw your attention to a little bit of verbal trickery in the first sentence: "human-unfriendly environment". This is not the same as uninhabitable, with acid rains, lead-melting temperatures, or hard vacuum. Sometimes, a planet is plenty alive... sometimes, too alive, with man-eating plants, semi- to hyper-evolved sentients, and scores of other dangers. A few old sci-fi serials and pulps would have their heroes' effort designed to create a "domestication" of savage planets, much like The American West was "tamed" with all the attendant heartache and extinctions.

More recently, some shows turn this around by showcasing how terraforming an already-living world can be ecologically disastrous, or ethically questionable, even weaponized. Or just plain pisses off the near omnipotent residents. Some works even turn the concept inside-out, showing how aliens arrive on Earth and mess the ecology up so badly that the planet becomes barely habitable, if at all, for humans (any similarities to Global Warming are entirely coincidental); this is sometimes termed xenoforming or un-terraforming.

As seen in the trope picture, Mars is likely to be a popular target for any terraforming operation in both fiction and reality. It has one of the shortest travel distances (second only to Venus), and is solid. Venus is also a popular candidate in fiction, being almost completely similar to Earth in terms of size and gravity, but it's second to Mars because warming something up is a lot easier than cooling it down, and unlike Mars, Venus's slow rotation would have to be dealt with.

Compare the Genesis Effect, for when an entire planet is actually created instead of just made livable.

Anime and Manga

 * Cowboy Bebop has numerous terraformed planets, moons and asteroids; it appears only small sections of Mars that are protected by some sort of force-field dome are livable, though on Venus the plants used to terraform could cause some people to develop "Venus Sickness" with such side effects as going blind. Ganymede is completely covered in ocean, while Titan is all desert.
 * Not force fields, air curtains.
 * Terraforming has become a necessity since inversely, Earth has become almost uninhabitable due to the moon getting destroyed and debris bombardment that continues.
 * Aria takes place on Mars, which got mostly covered with water from the pole regions after terraforming and subsequently got renamed to Aqua.
 * Zone of the Enders also features a partially-terraformed Mars. in Dolores, i, it's shown that some of the planet's oxygen supply is being generated by seaweed that has grown huge in the new environment, with fronds hundreds of feet long. You still don't wanna go out there for long without a spacesuit.
 * It's in progress on Mars as of the first Armitage III OVA. In the epilogue to the sequel, it get's oceans courtesy of a lot of dropped comets.
 * In Martian Successor Nadesico, Mars is terraformed through the use of Nanomachines. How these machines affected native Martians becomes a major plot point later on.
 * The beginning of an attempt to terraform Mars is mentioned in the finale of Gundam Wing. The sequel novel Frozen Teardrop has it completed roughly 20-30 years later thanks to an accident involving algae from Jupiter's moon Europa (previously studied but deemed too impractical).
 * Gundam AGE makes this central to the backstory. Around a hundred years prior to the series, a serious attempt at terraforming Mars was made. An unexpected and extremely deadly plague made the Federation give up,
 * Osamu Tezuka's Mazin Garon is a Humongous Mecha with the ability to alter planets to mimic the conditions of any other planet, even going so far as to be able to control gravity.
 * Near the end of Getter Robo Go,
 * The world-settlers in Trigun set out to terraform a new planet, but unfortunately ended up crashing onto a desert world (losing much of their tools and resources in the process) and what resources they still have are almost solely devoted to surviving. Due to this, the work has barely even started at the time of the series, and it's implied they'd already been there for several decades or more.
 * Almost all populated planets in Kiddy Grade became inhabitable through terraforming. One episode even has Ã‰clair and Lumi Ã¨re scavenge terraforming-equipment for usable parts.
 * Mars Daybreak features a Mars where terraforming has Gone Horribly Wrong, somehow flooding the entire planet except for the peak of Olympus Mons.
 * The bad guys in Space Carrier Blue Noah want to terriform the planet Godom for their own needs.
 * In Mahou Sensei Negima,

Comic Books
"Engineer: What would you call that? Un-terraforming? Monsterforming? Disgusting stuff. Turdscaping."
 * In the Wildstorm universe, it's eventually revealed that Earth was in fact terraformed by technology created by the ancestors of the Kherubim, who were far more Sufficiently Advanced than even the present-day Kherans were aware. This explains in part why humans and Kherans can interbreed; our DNA is partially based on theirs.
 * But in The Authority, another Wildstorm series, a totally different explanation was given at the end of Warren Ellis's run (not surprisingly, since it's Warren "What Do You Mean It Wasn't Made on Drugs?" Ellis). Here the Earth was placed in its proper orbit by what is, essentially, God: a pyramidal being the size of our moon with four thousand hearts and pores the size of Staten Island. God even placed some "watch spores" on the planet to make sure everything stayed perfect, then went off to wander the universe for a bit. In the meantime, a big chunk of something hit the Earth, then started orbiting, becoming our moon. By sheer chance, the watch spores were among the matter blown off by the impact. This tilted Earth's axis, altered the atmosphere, and eventually led to the development of life as we know it today. God eventually comes back to discover that its vacation home has suddenly developed a totally poisonous (to it) atmosphere and grown a six-billion-strong infestation. In order to return the planet to its "proper" state, God drops some disgusting organic machinery into the African veldt that begins restoring the original atmosphere. So it's not so much terraforming as un-terraforming.
 * The Engineer even tries to come up with a term for it:


 * In Buck Godot: Zap Gun for Hire, the Prime Mover (a Sufficiently Advanced Alien and Obstructive Bureaucrat) is Terraforming a planet as a hobby, in his room, by hand.
 * In his defense though, he did have a really big bucket.
 * Some of the Transformers comics written by Simon Furman have a variation of this: In the distant past, the war between alien gods Primus and Unicron was ended when Primus tricked them into eternal imprisonment in large metal planetoids. Over time, Primus terraforms his planetoid into the planet Cybertron (and creates sentient robotic life forms in the process), while Unicron terraforms his into a giant Transforming Mecha body.
 * Note that in Transformers Cybertron, the titular planet is also a Transforming Mecha. Primus just prefers to remain as a home for his children.
 * The Liege Maximo's Cybertronian Empire has a trend to terraform conquered planets to make them similar to Cybertron.

Film

 * Aliens is notable for showing at least part of the process, huge atmosphere altering plants.
 * In Red Planet, minimal terraforming efforts had been made to give Mars a breathable atmosphere. However, something went really, really wrong...
 * Total Recall does this to Mars, supposedly by rapidly melting the planet's icy core to flood the atmosphere with oxygen. All at once, with no harmful side effects to billions of tons of air suddenly blasting on to the surface faster than any tornado. A window gets broken, that's it. There's not even any dust kicked up. On Mars.
 * Maybe, it could have been All Just a Dream.
 * Titan A.E. had the Titan, which could completely and quickly remake a planet, just like the Genesis Device. Unlike the Genesis Device, though, the planet didn't collapse back on itself after a year.
 * The Titan didn't so much remake a planet, as make a whole new planet using a local nebula for raw materials. They just happened to call it "New Earth". Besides, we all know it's really called Planet Bob.
 * The Genesis Device from Star Trek II the Wrath of Khan turns a nebula into an Earthlike planet. Sadly, the planet tore itself apart within a year. If it had been used on a rocky planet instead of a nebula, the planet probably wouldn't have fallen apart if that terraformed underground location Khan imprisoned Kirk and co. in was any indication.
 * In Star Trek III the Search For Spock, David Marcus admitted that he had used "Proto-matter" (a highly-unstable element) in the design of the Genesis device. Even if Genesis had been aimed at a rocky planet, it would have fallen apart. There was never an explanation for the demonstration cavern.
 * Although it's not seen on-screen, the dialogue in Star Trek First Contact suggests that the Moon has been at least partly terraformed by the Next Generation era. When Riker, a Fish Out of Temporal Water, stands in awe at the sight of the 21st century Moon and Zefram Cochrane rolls his eyes and sarcastically asks whether they still have a Moon in the future, Riker answers that it simply looks "a lot different": in the 24th century, "Lake Armstrong" and several lunar cities are visible from Earth. This does contrast a few earlier episodes, where the 24th century moon put in an appearance and looked the same as ever.
 * It may just be possible that he was referring to it being colonized, not terraformed.
 * An inversion in The Arrival. An astronomer discovers that a worldwide rise in carbon dioxide levels and resulting global warming is due to aliens seeking to kill off humanity and make Earth more like their planet.
 * Possibly occuring to parts of Mexico and the US in Monsters (2010 film). Trees in the "Infected Zone" are being used to host alien spores.

Literature

 * The Trope Namer was science fiction writer Jack Williamson, who coined the term in a 1942 novella called "Collision Orbit."
 * Kim Stanley Robinson's Red Mars Trilogy goes into exhaustive detail about Martian terraforming.
 * H.G Wells' The War of the Worlds inverts this; the Martians try to areoform the Earth as part of their invasion plan. (Its publication date of 1898 makes this possibly the Ur Example of xenoforming.)
 * Another reverse-example is David Gerrold's War Against the Chtorr novels. Alien creatures are transplanted from their home planet to the Earth to replace our entire ecology.
 * And in John Christopher's The Tripods (which may well be an Alternate Universe sequel to The War of the Worlds), anti-Terraforming is on the Tripods' agenda somewhere after Enslave Humanity. The alien Masters plan to replace the Earth's atmosphere with one like that of their own planet.
 * Isaac Asimov's short story, "Founding Fathers," where a crew of multi-national astronauts crash-lands on an uncharted planet with just enough ammonia in the atmosphere to be unsuitable for human life. There are live plants on the ship, though, and if they can be coaxed to thrive somehow, a tipping point could be reached where the extra oxygen would wipe out the ammonia in a cascade. This is eventually done after a considerable time by burying the deceased humans in the crew into the soil. It is noted that the person who does this will not live to see the transformation finish (the ship's water supply got contaminated), and when this planet is discovered again, there would be no sign that there had ever been ammonia in the atmosphere...
 * In one of Philip K. Dick's stories, Earth and Titan were in an uneasy peace because of a war that was held because humans terraformed Mars. There were already people of Titan on Mars, but they couldn't breathe oxygen. By the time the humans learned of the Titanians, the terraforming had already begun, and "you can't terraform just part of an atmosphere..."
 * Many of the planets in Lois McMaster Bujold's Vorkosigan Saga have to be terraformed to a greater (Komarr: four hundred years of domed living, with another four hundred to come, while the solar mirror array and genetically engineered plants make the atmosphere breathable and warm enough) or lesser (Barrayar: dump Earth soil and Earth-descended plants in place and burn away the native stuff; well, at least until the butter bugs start working) extent.
 * In Larry Niven's Known Space universe, most life-bearing planets were seeded with life by the Slavers; not to terraform, but simply to grow enough food for their vast and inefficiently-run empire. Specifically most planets only had a strain of yeast their prey animals enjoyed eating. When the Slavers War ends with the Suicide Night that kills all life on the level of lobsters and higher in the entire Galaxy, the majority of life evolves comes from their yeast farms, which explains why we are biochemically compatible.
 * The results of unfinished or untended Terraforming is a large feature in Niven's work. Earth was partly Terraformed by the Pak, with the issue there's not enough thallium for the Pak's final lifestage to complete. Ringworld has much of the same issue being explored with humanoids left alone on a mostly terraformed Ringworld until they differentiate into ecological niches.
 * In Niven's A World Out Of Time, delivering biological terraforming packages to suitable extrasolar planets is the job given to the corpsicle Corbell.
 * In the CoDominium universe, New Caledonia is a formerly barren world still being terraformed; for already life-bearing planets, the process is more a matter of altering the local ecology to support Earth life (which is usually grossly simplified for story purposes).
 * Riverworld is set on a planet terraformed into one big twisting river valley, to maximize the surface area ideal for human habitation.
 * The Robert A. Heinlein story Farmer In The Sky is about a terraforming effort... on Ganymede.
 * Dan Simmons' Hyperion universe has in its backstory humanity terraforming all their worlds, regularly committing genocide against sentient indigenous species. This bothers pretty much no one, human, AI, or transhuman.
 * The major theme of Dune is the back-and-forth attempts by humanity to terraform the desert planet Arrakis inhabited by the various life-cycle stages of sandworms (which create an extremely necessary commodity) and by the (non-sentient) sandtrout phase of the worm species to counter terraform Arrakis (and later other worlds) back into desert.
 * Honor Harrington has a major factor in the economics of the various colonies being how well they were terraformed. This is largely a function of when you left Earth and how much money you had when leaving. Haven and Manticore were settled fairly late with good resources. Other planets like Grayson were settled by cold sleepers who left very very early, had poor terraforming technology, and ended up on a planet full of heavy metal poisoning.
 * The state of the terraforming efforts combined with the cultural base also give planets such as the Albino Zulus whose gene engineered solution to a poor Ozone.
 * In Manticore's case it's stated that the only terraforming that was needed was the introduction of a few Terran plants, and that the unusual compatibility of the native life allowed a hybrid plague to develop.
 * And it's probably no coincidence that the most populous planet in the Manticore system is the one that doesn't have high gravity or turbulent storms.
 * The Magratheans seem worthy of a mention, taking this idea to its logical extreme by creating a custom planet-building business.
 * A. E. van Vogt's Voyage Of The Space Beagle: Anabis, a galaxy-spanning consciousness that has terraformed all planets in its own galaxy by ripping a piece of its planets surface off and sending to to the target planet through hyperspace (called junglescaping).
 * Like the Magratheans two entries above, Roger Zelazny's character Frank Sandow in Isle of the Dead and To Die in Italbar made a business of building planets, to order, or to his own design. Near the end of the first book, he has a vision of every planet he's built. After seventeen names, it trails off with "and so on." (He's over twelve centuries old; he's had time.)
 * In Robert Charles Wilson's Spin, when the Earth is placed under a membrane that slows down time (which means that for the people of Earth the Sun will expand in a few decades), humans successfully terraform Mars; a whole civilisation appears there within a few years (for those on Earth)/a few millennia (for the people of Mars - humans who have evolved slightly differently.)
 * The major plot element of the New Jedi Order. Picture a cross between Super Saiyajin and species 8472.
 * Cthulhu's Reign, edited by Darrell Schweitzer, is a Cthulhu Mythos anthology of short stories on what life existence on Earth would be like if when the Old Ones return. There are several references to the Eldritch Abominations 'terra-deforming' the Earth so it's more suited to themselves.
 * In one Arthur C. Clarke novel Mars is being terraformed by selection and spread of oxygen-generating plants native to Mars, as well as by turning Deimos into a coninuous thermonuclear explosion, effectively providing the planet more sunlight than the Earth gets for a hundred years.
 * In Helm, Epsilon Erdani II -- known to its settlers as Agatsu.
 * In part three of Alexander Kazantsev's Destruction of Faena, Mars' surface is made inhabitable by bombarding it with rockets made of ice, which melts, creating the first ocean.
 * Savior by Robert Reed - A rapidly failing alien starship uses a massive laser cannon to melt the ice bergs to try and make the Earth habitable for them. Naturally, this doesn't go to well for the aliens.

Live Action TV
"Dave Lister: Remember, it's Rimmer's mind out there. Expect sickness."
 * Andromeda has the Pyreans, aliens who exist on planets like Venus -- super hot, toxic, and deadly to most organic life. They "pyroform" planets by burning them to their tastes, the old Commonwealth had to seriously fight them not to lose precious human habitable worlds.
 * Firefly, where every planet and moon in the system is terraformed. The terraforming is mainly done by massive machines brought from Earth-That-Was, but human labor is still needed and it's hard, dangerous work.
 * Plus, terraforming often has unintended side effects, like the newly introduced atmosphere interacting with minerals or gases to cause a massive plague, and at least one planet is considered an uninhabitable "black rock" because the terraforming never took.
 * In Babylon 5, humanity is in the first stages of terraforming Mars.
 * Star Trek the Next Generation had a surprisingly good first season episode where the Enterprise was trying to help terraform a desert planet by pumping water for irrigation. Unfortunately, the planet was occupied by sentient lifeforms who were annoyed enough at the attempt to terraform to sabotage the drill. It took a while for everyone to figure this out because they were microscopic silicon lifeforms, and so were mistaken for parts of the sandy scenery.
 * However Federation Terraforming regulation require a planet to be devoid of any trace of life, so not even possible future species might be prevented from evolving naturally.
 * Star Trek Enterprise has Mars terraforming in-progress. They had the atmosphere thickened enough to allow people on the surface without pressurized suits, and that's about it. By 2155 you still need oxygen tanks and thick clothing to stay alive.
 * Stargate SG-1 has two whole galaxies full of planets terraformed by the Ancients and the Goa'uld, complete with Transplanted Humans.
 * They also had a "pyroforming" species, similar to the Andromeda example above.
 * Except these were Actual Pacifists, who wouldn't fight back when they were attacked by the Goa'uld. They have no problems "pyroforming" a world fill with plant and animal life, though.
 * Red Dwarf did it twice, both due to Rimmer and both resulting in complete catastrophe.
 * The first episode, "Terrorform", was based on a sentient moon which formed itself based on the psyche of those who landed -- and it's long been established that Rimmer's psyche is not a good place to be...


 * The second time was "Rimmerworld", where Rimmer, abandoned to his own devices (by his own cowardice) on an uninhabitable world for 600 years armed with only a planet seeding pod, creates a Single Biome Planet of Rimmers -- he lasted barely forty years before being slung in jail by the rest of him.
 * Terraforming was the backgound plot of  Back to Reality: Planet engineers in an ocean seeding ship had terraformed an ocean moon and created a marine ecosystem teeming with lifeforms by vastly speeding up evolution. Unfortunately it backfired when one lifeform arose that wiped out everything else: the Despair Squid.
 * The Cosmos episode "Blues for a Red Planet" discussed the possibility of terraforming Mars with dark-colored, hardy plants.
 * Doctor Who
 * In the episode "The Doctor's Daughter", the planet Messaline is turned from a desolate wasteland into a beautiful planet full of life by using a terraforming device.
 * In Terror of the Zygons, the Zygons planned to modify the Earth’s climate to make it more suitable for their species.
 * The Twilight Zone 1980's remake episode "Voices in the Earth". All life on Earth was wiped out and the planet made uninhabitable by a disaster a thousand years ago, including changing the atmosphere to methane. At the end of the episode a group of ghosts restores the biosphere, including changing the air back to normal, recreating life in the oceans and accelerating its evolution.
 * The Neo Frontier of Ultramn Dyna was a terraforming project to colonize the solar system. during the series itself, Settlements had been created on Mars.

Tabletop Games

 * The Mutant Chronicles universe has a terraformed Mars and Venus.
 * Let's not forget about various asteroids, moons and the caves on Mercury.
 * In the Centauri Knights setting for BESM, the planet being colonized has had its ecosystem wiped clean to the bedrock by Nanomachines made by the natives. The native ecosystem survives on a couple of still-working, but unoccupied, space habitats near the planet. One of the conflicts in the game's politics is: do we terraform the planet into a new Earth, rebuild its own ecosystem by transplanting from the colonies, leave it a barren desert and mine it for technology, or abandon it and go home?
 * In Yu-Gi-Oh!, there's a card called "Terraforming" that lets you search your deck for a field card. You literally make the environment more friendly to your creatures -- whether human, beast, angel, demon, crystals, etc.
 * In Warhammer 40000 this is done by two factions, and inverted by a third.
 * The Imperium either terraforms any worlds it settles that are not already inabitable by humans, or turns them into polluted hyper-urban hive worlds.
 * The Eldar Maiden Worlds are worlds undergoing long-term alteration to make them inhabitable by Eldar Exodites or (voluntary) outcasts. Non-Eldar races settling a Maiden World are... strongly encouraged to leave.
 * Inverted/Subverted by the Necrons, whose idea of creating the perfect environment is to purge it of any and all life.
 * The Tyranids, of course, "Un-Form" planets, stripping them of every resource. They eat the local wildlife, including humans, and vegetation, strip elements from the atmosphere, bio-mine anything they can from beneath the surface and leave a dead husk of useless rock.
 * Buck Rogers in the XX Vth Century. Mars, Venus and Titan (the largest moon of Saturn) are all in the process of being terraformed.
 * Life on most of the Known Worlds in Fading Suns is supported by ancient terraforming engines, unfortunately many of them are now failing.

Toys

 * Mata Nui does this as he reforms Spherus Magna in Bionicle, making parts of the desert Bara Magna into jungle, mountains, etc.

Video Games

 * The Scrin are doing this to Earth in the latest Command and Conquer game. It may be the whole reason Tiberium landed on Earth.
 * It turns out this isn't terraforming, it's just a massive mining operation. Tiberium sucks up all resources, then the Scrin collect the Tiberium and go home. They wouldn't have shown up yet, but Kane tricked them into arriving early.
 * Its also an effective Depopulation Bomb. Tiberium devastates the environment and disrupts ecosystems, causing widespread famine and sickness. At the same time, it offers the native population plentiful resources to manufacture equipment and weaponry. Intense social pressures + massive availability of material to construct weapons = total implosion of the local population and devastating wars that crush the remainder of civilization. Generally, by the time the Scrin arrive, the locals have wiped themselves out or been killed off by the transformation of their planet.
 * Sid Meiers Alpha Centauri has terraforming as a big part of the gameplay, even allowing you to decide how much you want to incorporate the native environment (which is a good idea, because this environment fights back!).
 * Freelancer has no terraformed planets, but instead has terraforming planets like California Minor. It also shows a little bit of the process with Planetform, Inc., the company that handles terraforming operations, and by letting you trade stuff like terraforming gases, alien organisms that eat carbon dioxide and release oxygen, and H-Fuel to power these operations. The game also features the Gaians, a rebel faction of Well Intentioned Extremists who firmly believe that terraforming is the same as ecocide.
 * Not that all these efforts are successful. A Planetform NPC in Bretonia mentions that the efforts to terraform a planet in Bretonian borders has had mixed results. Although habitable, the planet is mentioned to be suffering from bouts of extreme weather and the NPC mentions it will revert to its original state as soon as Planetform packs up and leaves.
 * Inverted in Half-Life 2 when the invading aliens, the Combine, aim to strip the planet of its atmosphere and water leaving it desolate and uninhabitable. An effective reverse terraform.
 * The Mycon in Star Control 2 use their "Deep Children" to pyroform worlds to their standards.
 * In KOTOR II, one of the planet/levels that you visit, Citadel Station, exists for this purpose. This is unique, however, in that the planet, Telos, was originally habitable, but the Sith razed the planet for no particularly good reason.
 * The third game in the UFO series, Afterlight has this as much of the point. Humans, forced off of Earth, travel to Mars to create another habitable planet. Terraforming technology very slowly changes the red planet to a blue and green planet in real-time, and tactical combat maps change from red and deadly to green and (relatively) safe. In fact, if you fail to start the terraformation process shortly after the beginning of the game, the environmental hostility will quickly go out of control, and your space suits will not protect you. The terraformation is also shown in "stages", with the dead, red planet as stage 1, small "plant" organisms and cacti as stage 2, and the appearance of water and more complex organisms as stage 3.
 * Terraforming Mars is mentioned in Doom 3. You have to go outside a few times, and you can last only a few minutes.
 * In the first two Master of Orion games, terraforming goes on for much of the game. Together with the tech for planetary gravity generators, radiation shields, enriching biospheres and installing biospheres, it's possible to transform an empire into a verdant garden where previously inhospitable planets have between three and fifteen times their original population limits. In the second game it's then possible to fashion asteroid belts and gas giants into new planets and terraform them as well. It's great fun for those who get attached, and well out of place in games of galactic politics and warfare where genocide is what's for dinner. The third game has Spore -- like circles and something about "Terra approxima".
 * Interestingly, despite the ability to take a gas giant, squeeze it into a rock, and turn that rock into a lush world, you can't de-toxify a planet. Possibly, an oversight on the part of the creators. The only alternative is to destroy the planet with a Stellar Converter and then rebuild it into a world of your liking.
 * Galactic Civilizations 2 gave various levels of terraforming, which would each make a planet slightly more habitable. In the later expansions, planets with extreme conditions were introduced which required special technology to be researched even to colonize.
 * The old 4X game Ascendancy had terraforming as something that could be done only after discovering a fairly high-level technology. In this game, all territory considered of "squares", which could be different colors, each color corresponding to its suitability to different tasks (green for prosperity, red for industrial, for example). Black squares were uninhabitable (except to one species) unless terraformed. Further, the Lush Growth Bomb project increased the maximum population of a planet.
 * Very mild degrees of terraforming take place in Mass Effect, as the process is noted to be extremely expensive. Generally, the various species just look for planets that can sustain their biologies naturally, which are few and far between.
 * Present in Spore, where using various upgrades to your starship, or purchasing other, various, one-shot machines, you can improve the "T-score" of a planet (which range from T-0 to T-3), which allows it to sustain life better, which, in turn, allows you to plunder it for more Spice to sell.  Colonized planets can only sustain a number of settlements equal to the T-score. T-0 planets can be claimed by placing a colony, but they will not be able to produce any spice until the atmospheric conditions are improved and then a basic ecology is introduced, establishing a T-score of at least T-1.
 * It's also possible to deterraform a planet, lowering the T-score, reducing its habitability and extincting its indigenous lifeforms. Doing this on a foreign planet is considered an act of war (while improving a foreign planet's T-score can earn you their gratitude). It is, however, one of the simplest strategies for wiping out or conquering the home-world of a hostile race before your ship has top-tier weaponry available. Home-worlds are almost always T-3s with extra settlements (as many as 10 fully defended sites with fleets of defending ships). Using terraformer tools to lower the T-Score even a single level will wipe out almost all the settlements, leaving the place far more vulnerable to conquest or extermination and recolonization.
 * Star Fox: Andross apparently planned to terraform Venom, a rather barren planet with acidic oceans. In Command, this becomes central to the better endings since these oceans are also the home of the hostile Anglar. In 2 endings, his invention is used successfully and causes Venom to be as fertile as Corneria.
 * The simulation game Outpost had terraform-buildings available in the late game. Of course, it took an inordinate number of turns for them to complete their job, and successful terraforming provided no real benefit over the life-support buildings you had since Turn 1.
 * Outpost 2, in its Genre Shift to real-time strategy, made terraforming into the cause for the game's plot -- a huge increase of natural disasters and the unleashing of an all-consuming biological nightmare likely to be The End of the World as We Know It. Second world, that is -- Earth was already gone by that time.
 * Perimeter has terraforming as important game mechanic. Not so much terraform the whole planet as local area, but idea's the same.
 * The Machines' primary function before they get into a war.
 * In Imperium Galactica II you can use Genesis-type devices on planets that explosively terraform them to your civilization's needs.
 * Another 4X game, Sword of the Stars, has terraforming as a mandatory part of colonization. You can get techs that boost terraforming speed and the range of environments that are cost-effective to terraform, though some planets will always remain out of reach. However, since up to five different races can live on a planet at a time, all with different ecological backgrounds, sometimes some population juggling is necessary. It's possible for a race to colonize planets that are completely inhospitable to another - and conquering these planets instantly pops their habitability zone right to yours (when using assimilation plague missiles). Useful when most planets are hostile.
 * The "aliens" in Hostile Waters embark on a great xenoforming project of Earth itself, starting with Greenland. Given that they are, in part, living universal constructors, it becomes of vital importance to stop them.
 * Haegemonia has terraforming capabilities for all races. Planets can be sorted into four groups: for humans, the first group is gaia/terran/oceanic (can be colonized from the start), the second is forest/swamp/desert/arctic/plains/volcanic/rocky (needs research), the third is barren/acidic (needs more research) while the final one is gas (uninhabitable). Kariaks and Darzoks have different qualifications; for example, both like barren. If it's not good enough, it can be terraformed once which improves the quality of the planet; once the next level is researched, it can be terraformed again. For example, level 1 human terraforming can turn plains into forest while level 3 instantly pushes any planet to oceanic/terran. In the expansion The Solon Heritage, spies can actually reverse-terraform, causing an ecological catastrophe (talk about overkill...).
 * Final Fantasy IV: The After Years reveals that the Four Elemental Crystals that show up in so many games of that series are actually terraforming implements. They're a bit less reliable than slower methods though, given that their terraforming effects tend to wear off once they're removed or destroyed.
 * Egosoft's X-Universe games have terraforming as the event that started the whole series. After a glitched software update, the machines that man had sent out to terraform the system started terraforming everything, including inhabited planets and ships. Mankind fights back, the terraformers swat them out of the way, and all seems lost until they're tricked into moving en masse to a distant part of the universe -- which they promptly start terraforming as well.
 * Escape Velocity: In these games, Mars was always the first planet to be terraformed. And it always went very, very wrong, and the next few hundred years are spent trying to fix the mess.
 * EV Nova also lets you see somebody get terraforming right in one quest line. And the Polaris have largely mastered it, with several planets listed as terraformed in the "communicate with planet" dialog box.
 * Starting from Space Empires IV, you can terraform a planet's atmosphere to suit your population.
 * Fallout has an example in the Garden of Eden Creation Kit (GECK), which turns several square miles of nuclear wasteland into a lush, green paradise.
 * Fallout 3 featured one side-quest involving a mutated tree and it's offspring which are (thankfully) non-hostile and thriving in the wasteland. A small cult has sprung up around worshipping this tree and they believe it may eventually re-terraform the entire planet (or at least the DC area) into a state more capable of sustaining life and human populations.
 * Star Wars: The Gungan Frontier has the player setting up a complete ecosystem on one of Naboo's moons so the Gungans can colonize it.
 * In Jeff Wayne's War of the Worlds, much like the novel, the Martians engage in xenoforming with their red weed.
 * Champions Online features as a mid-level quest chain fights against the froglike Gadroon who are seeking to Xenoform Earth into a much warmer, swampier habitat -- starting in the middle of Canada.
 * Lost Planet, though the original plan for making E.D.N. III hospitable would have fried the Akrids and more importantly the colonists already on the planet.
 * Sim Earth has terraforming machines for its Mars and Venus scenarios.

Web Comics

 * Freefall is set on an alien world which is in the process of being terraformed.
 * A Miracle of Science has a terraformed Mars that has become a Hive Mind of post-human and AI inhabitants.
 * They also terraformed Venus and Europa to give the rest of pre-singularity Humanity more places to live. In the case of Mars and Venus the process is still ongoing: Venus is constantly raining, while one character (a Martian of course) works on a project to restart Mars' plate tectonics and make the atmosphere self-sustaining.
 * In The Inexplicable Adventures of Bob, Butane, the planet of dragons is a terraformed world in the Kuiper Belt. Jolly the Giantess has been given the job of helping to maintain it.
 * In Schlock Mercenary Mars, Venus, Europa, and Luna (Earth's moon) have all been terraformed.
 * This becomes a plot point when they visit a planet which hasn't introduced many oceanic species because its economy is based on tourism and ocean resorts. There are a few deaths which look like shark attacks, and the first suggestion offered by a character is that someone made a robotic shark with a robotic jaw to murder people.
 * Far Out There uses this to explain its habitable planets (as well as why Trigger grew up in an underground bunker)
 * In Campus Safari the Cyantians are terraforming Mars and Venus as gifts for humanity when they make First Contact. Their colony on Mars doubles as a Wacky College.
 * In Homestuck,  tries making Earth more like her homeworld Alternia, introducing Alternian life and flooding the planet.
 * She also tries to subvert human culture to more closely resemble her species', but it fails miserably because of basic biological differences (really basic differences). Her attempts to genetically alter humans to use the Alternian mode of reproduction and blood castes results in complete extinction.

Western Animation

 * Some Transformers continuities have a thing called cyberforming, whereby a planet is made suitable for Transformer life.
 * In some continuities Unicron was originally created as a quick and dirty terraforming engine by an alien named Primacron. He was meant to eat lifeless rocks and shit out planets suitable for habitation, but he decided to skip step two and absorbed planets of any kind into himself to increase his power.
 * In Exo Squad, Mars and Venus were terraformed. This is a key part of the Backstory, since it's the job the exoframes and Neo Sapiens were invented for.
 * In Aqua Teen Hunger Force, the crappy clone of Master Shake made by the Plutonians is sent to Earth to "de-terraform" it. This plan is not well thought out. Not only does the clone not feel obligated to do so, it has no idea what "de-terraform" means, or how he'd do it, or if it is in fact a real word.
 * Mars has been terraformed in Futurama, as explained in the opening quote. Later episodes, however, show that much of the planet is still desert. Oddly enough, the native Martians that still live there don't seem to have any negative effects from the wholesale transformation of the atmosphere.
 * In the Phineas and Ferb episode "Moon Farm", the main characters decide to terraform the moon so that they can take cows there, and make the best ice-cream ever, as detailed in the lost sacred stanza of "The Cow Jumped Over The Moon".

Real Life

 * The Earth, in its long existence, has had three atmospheres. The first, composed of hydrogen and helium, is believed to have been blown by the solar wind. The second, believed to have been formed by volcanic outgassing, was around 100 times as dense as our current atmosphere, and composed mostly of carbon dioxide with some nitrogen. This was converted into our current atmosphere by two processes. One, the carbon dioxide was scrubbed by chemical interaction with minerals dissolved in the oceans, forming carbonate rocks. Second, the development of photosynthetic bacteria started producing oxygen, which eventually built up in the atmosphere.
 * Venus is basically stuck with a stage two atmosphere, because it lacks water. Possibly something to do with being too close to the sun, and thus outside the habitable zone. Earth had, literally, oceans of water even early in its existence. Where the water came from is still a subject of debate. But water is necessary for the carbon sequestration that removed most of the carbon dioxide from the stage two atmosphere.
 * Terraforming planets, by current human technology standards, is possible, but scientists theorize that any such process to turn a completely uninhabitable planet into a habitable one would take hundreds of years, perhaps even a full millennium. Planets that are closer to Earth standard might be capable of terraformation in as little as 300 years. So, don't count on it. (As a point of interest, many scientists theorize that Venus would be a better candidate for terraformation, instead of Mars, due to the fact that Venus is tectonically active, while Mars isn't.)
 * NASA's even done studies on the idea of terraforming the Moon into an Earth-like world. While the lunar gravity's too weak to hold a permanent atmosphere, it'd take thousands of years for a newly created one to dissipate, and in the meantime the Moon could conceivably have blue skies, oceans and forests. It seems like a colossal waste of resources by today's standards, but the possibility does exist for any future civilization that really wants to go sunbathing on the Moon.
 * One of the problems with terraforming is an ethical one. If, hypothetically, there exists microbes on Mars (which is possible), Terraforming would likely lead to its extinction. This may seem insignificant until you realize that humanity had also evolved out of microbial life, so we would potentially exterminating intelligent life before it is even able to evolve to that point. This is the subject of a lot of debate within the scientific community with some in favor (Mars Society founder Robert Zubrin, for one) and others opposed (such as the late Carl Sagan).
 * An added difficulty of any theoretical terraforming that real life scientists have seriously discussed is also the issue of maintenance of the terraforming. It would be pointless to expend so much time and effort to terraform a planet only to have it undone. This is one of the reasons why some consider Mars a poor candidate. Mars's core has long since hardened, which means it has no magnetic field to protect life from solar radiation and from solar winds blasting away its atmosphere. The atmosphere Mars now retains is a mere wisp compared to what scientists theorize it may have once had.
 * Mars has some issues with potential terraforming, but atmosphere retention isn't really a huge problem. The planet could hold on to a breathable atmosphere for tens or possibly even hundreds of millions of years, unlike a possible terraformed Moon.
 * This is largely conjecture, but if the atmosphere is being blown away over millions of years is it really that absurd to import atmosphere to replace it as it is blown away? To even settle Mars at first would require at least some level of casual inter-planitary travel.
 * To an extent, terraforming is already happening right now, here on Earth: Human beings have been "reclaiming" land from the sea for centuries, particularly in the Netherlands, Hong Kong, and Dubai.
 * Also, this. Darwin did it first, guys.
 * The age of a star can change the conditions of whatever planets orbit it as it grows bigger and hotter as it ages by pushing the habitable zone (an invisible boundary where liquid water can exist) outwards. While doing so will render any planet originally in that habitable zone uninhabitable, it will also make planets too cold for life to become warm enough for life to evolve. When our Sun dies in about 5 billion years, this will actually happen to all of the outer planets in our Solar System. In fact, even Pluto may eventually become Earth-like one day!