Living or occurring only in the presence of free oxygen. An aerobe is an organism that requires free oxygen. On Old Earth, eukaryotes and many prokaryotes are aerobic.
- Anaerobic - Text by M. Alan Kazlev
Living in the absence of free oxygen; pertaining to or caused by the absence of oxygen. Eogaian planets are characterized by anaerobic conditions. An anaerobe is an organism, such as a bacterium, that does not require free oxygen to live (opposed to aerobe).