Quotes About Biospheres

Space settlements would also contain biospheres replicating Earth conditions and atmosphere.

Complex biospheres like the Earth's could be rare because of some bottleneck, some key stage in evolution, that is hard to transit. Perhaps it is the transition to multicellular life. (The fact that simple life on Earth seems to have emerged quite quickly, whereas even the most basic multicellular organisms took nearly three billion years, suggests that there may be severe barriers to the emergence of any complex life.)