Although Heidegger’s interests were focused on the question of the meaning of Being, our contribution shows the possibility of an ontology of life based on the concepts of “world” (Welt) and “finitude” (Endlichkeit) developed in his philosophy of the late 1920s. We begin by explaining the question of finitude and the reason why Heidegger differentiates between the dying (sterben) of Dasein and the perishing (verenden) of living beings (SZ, §§ 46-49). Although we cannot characterise living beings thanks to the concept of Being-towards-death, we must admit that in the case of living beings, it is also true that no one can take their perishing away from them: no one can die for them. It is worthwhile to bring to light not only our everyday vague understanding of the finitude of living beings, but to reflect on the points in common between their finitude and our own. By doing so, we discover that Dasein encounters living beings in its world. This leads us to an explanation of the difference between “world” (Welt) and “environment” (Umgebung) (GA 29/30, §§ 42ff.), to the introduction of the concept of environmentliness (Umgebunglichkeit) and to the defence of an extension of the concept of “common world” (Mitwelt) to include living beings.