Terraforming

Terraform was a word for the deliberate alteration of a planet's atmosphere and ecology to create an environment suited to human life. The word came from the Latin word Terra, meaning Earth.

Examples of terraforming
The Tenth Doctor used an atmospheric converter to clear the skies of Earth from ATMOS poison in 2008. Luke Rattigan later used the same converter to blow up the Tenth Sontaran Battle Fleet and save Earth from invasion. (TV: The Poison Sky)

Mitzi, the first cat to go into hyperspace, landed on the planet Photris, which was terraformed. (PROSE: The Cat Came Back)

In the 25th century, Kano Dollar had the ice planet Isen VI into a jungle paradise. Unfortunately, this also awoke the Hyperion Rann-Korr. The Twelfth Doctor reversed the planet's terraformation, causing at least part of it to return to its original state. (COMIC: Terrorformer)

In the late 25th century, Planet Hollywood was terraformed by a consortium of entertainment businesses. (PROSE: Peacemaker)

According to one account, by the 26th century, Mars had been completely terraformed by humans to make it habitable. They melted the icecaps and installed a gravity web to make an Earth-like planet, albeit with less gravity and more UV light. (PROSE: GodEngine, Beige Planet Mars)

According to another account, the Monk tried to alter history to make the Ice Warriors terraform Mars to make it as it was millions of years before the 23rd century and prevent the Ice Warriors from altering Halcyon's ecosystem, but was unsuccessful. While repairing the atmospheric re-ioniser for the Ice Warriors' use, the Eighth Doctor had altered the re-ioniser to make Mars' air 80% nitrogen and 20% oxygen. The destruction of Deimos Moonbase also lit up Deimos, making the moon into an artificial sun that heated Mars to make it warm enough for humans. (AUDIO: The Resurrection of Mars)

Before the 40th century, Io was terraformed for use as the headquarters of the Galactic Federation. (PROSE: Legacy)

During the Second Great and Bountiful Human Empire, Agelaos was terraformed. (PROSE: The Story of Martha: The Weeping)

In the 49th century, humans terraformed Alfava Metraxis. (TV: The Time of Angels)

The Source was a creation myth for the people on the planet Messaline. The Tenth Doctor, Donna Noble, Martha Jones and the Doctor's daughter Jenny discovered it was a terraforming device. The Doctor released the device to trigger the terraforming of Messaline in 6012. (TV: The Doctor's Daughter)

After Earth and Mars became uninhabitable, Pluto was terraformed by the Usurians. (TV: The Sun Makers)

Shanquis was terraformed using human technology. Even after the humans died out, the terraforming devices could be activated by spoken English. (AUDIO: Bernice Summerfield and the Criminal Code)

Osphogus was terraformed. It was still inhabited five thousand years later. (AUDIO: The One Doctor)

The See-yee tried to terraform Earth, but the Eleventh Doctor made the device malfuction so it produced a jungle. (AUDIO: The Runaway Train)

Similar processes
Technically, terraforming was the transformation of a planet to a more Earth-like form, but other species had similar processes to adapt planets to a form more like their own home planets.

Theoretical Monsters: A Credibility Test referenced the Kalekani, a species who used a terraforming virus which converted land into flat grassland, effectively turning it into a golfcourse. Fitz Kreiner believed they were made up. (PROSE: Interference - Book One)

In 1864, the Cei sent a terraforming device to Earth so it could be used as an outpost. (AUDIO: The Runaway Train)

In 1997, the Ice Warriors planned to wipe out the humans and terraform — more specifically, areoform — Earth, but they were unsuccessful. (PROSE: The Dying Days)

The Cthalctose created a terraforming device called the Genesis of Cthalctose. It sparked the Agent Yellow crisis in 2003. (PROSE: Eternity Weeps)

Torchwood Three speculated that the Vandrogonite Visualiser was intended as a terraforming device. (PROSE: Pack Animals)

The Ice Warriors attempted to terraform Earth again in the early 21st century using a Martian fungus. (TV: The Seeds of Death)

In the 22nd century, the Daleks terraformed (or, technically, skaroformed) Antalin to resemble Skaro. (PROSE: War of the Daleks)

Around the 33rd century, the Ice Warriors terraformed Halcyon, making it habitable to Martian life, but hostile to humans and the 20 billion Halcyon. (AUDIO: The Resurrection of Mars)

The Daleks somehow terraformed Jupiter. They changed it from a gas giant to a planet that humans could survive on. (AUDIO: Dalek War: Chapter Two, Dalek War: Chapter Three)

Terraforming was meant to modify the eco-system of a planet so that it resembled Earth and could be inhabited by humans. The humans did that to a lot of planets. However, terraforming could destroy the minerals that some humans wanted to mine. This was why the humans started to adapt. They modified their bodies to suit the alien environment. They completely reworked themselves and had new DNA sequences and new organs. (AUDIO: The Nu-Humans)

Terraforming technology and companies
Geo-forming was like terraforming, but much faster. (AUDIO: The Survivors)

WorldCorp and PlanetScape were both human terraforming companies. (PROSE: Dark Progeny)

Nooma was artificially created to test terraforming technology by the Aapex Corporation. (PROSE: Speed of Flight)

A Terran Federation ship carried terraforming equipment. The Sontarans took the ship and planned to use it to create cloning planets. (COMIC: Pureblood)