One sign that a planet probably already contains life is the presence of an atmosphere with significant amounts of oxygen, since that gas is highly reactive and generally would not last long without constant replenishment.
Awa isaknen as planète ihet hulanen dat awa tamudre eqal tajayhit ən atmosphère dər haditan atiwagrahnen noxygene, falas gaz wen eqal hulen aynakaran əd izar waritihigu deqanen hulen aswiden agay ən harkuk.