Biosphere

The biosphere is the part of a planet where life occurs, including the atmosphere, water and terrain.

The practice of terraforming takes a barren, lifeless planet, and transforms it into one with "a lush, arable biosphere." 

The Millennium Gate was a self-sustaining city build on Earth during the early 21st century that was an experimental biosphere, the first of its kind. Shannon O'Donnell, who was learning about the project, explained these facts to Henry Janeway in 2000. Janeway thought the entire project was unnecessary, asking O'Donnell, "what's wrong with the biosphere we're living in now?" O'Donnell explained that nothing was wrong with it, but the project as a whole would "help scientists learn more about our environment. Possibly even recreate it on other worlds."

In 2369, Klingon Captain Nu'Daq of the collected a DNA sample from the planet Indri VIII. To prevent any others from collecting any more DNA from the planet, he proceed to destroy the biosphere by initiating a plasma reaction that globally consumed the lower atmosphere of the planet, destroying all life on the planet. 

In 2372, the USS Voyager discovered a planet that had survived a solar flare, which occurred on the planet in 2353. As a result of the flare, the planet experienced radically changing weather patterns, magnetic storms and extreme levels of radiation, yet by the time Voyager discovered it, they found that the glaciers were receding and the biosphere was in the process of recovering. 

In 2373, the Maquis, under the direction of Michael Eddington, attacked the Cardassian colony on Veloz Prime with a biogenic weapon. As a result, the weapon spread cobalt diselenide (a nerve agent deadly to Cardassians) throughout the planet's biosphere, making the planet uninhabitable to the Cardassians, but suitable for the Maquis, who intended to reclaim the planet. In retaliation, Captain Benjamin Sisko detonated his own biogenic weapon in the atmosphere of the Maquis planet, Solosos III, which scattered trilithium resin into the atmosphere, making the planet uninhabitable to all human life for the next 50 years.