Hello, I think this likely has been suggested before and may even be a mechanic already, If so i apologize but would it be possible to set planets too posses a biosphere. Most planets already have hydrospheres and tectonics so it doesn't seem too be too much of a leap to develop biospheres on planets though the biospheres would be limited by:
1) liquid water, no life can exist without water so liquid water or ice sheet would be neccesary for the planet to sustain life.
2) the biospheres could make terraforming more interesting as you'd need to change the local flora and fauna to make it easier to sustain life, though seperate ecosystems wouldn't be too much of a leap and affect colonisation over much, say if a planet has hostile fauna which uses a different substance than cellulose for plants itd be more difficult for colonisation as the colonists would need to handle the aggresive wildlife as well as find a way to metabolize the plants. Though this would cause changes to other mechanis so it need not be useful.
3) temperature, covered by liquid water, too hot and nothing can live, ditto too cold.
This is just a question as i've been thinking about what it'd be like for colonists to set up on a planet without having to handle native life if the planet isn't a barren rock.
The idea is to have multiple levels of biosphere such as cellular: just developed, earth-like, developed enough to have complex lifeforms, hostile: death worlds containing aggresive plants or animals that are a threat to the colonists.
