Unlike Earth, where organisms generate and maintain a 21% oxygen atmosphere, Europa's oxygen atmosphere is produced by purely non-biological processes.
(Earth; generate; organisms) (organisms; maintain; a 21% oxygen atmosphere; L:Earth) (Europa's oxygen atmosphere; is produced; by purely non-biological processes)
Earth organisms Europa's oxygen atmosphere
generate maintain is produced
organisms
a 21% oxygen atmosphere L:Earth
by purely non-biological processes