Plotinos: Complete Works, v. 3 In Chronological Order,...

3. (It might however be objected) that the body of the world could not contribute to the immortality of the world, since the body itself fluctuates perpetually. But this fluctuation does not take place in an outward direction, while the body (of the world) remains ever the same because this fluctuation occurs so entirely within the world that nothing issues therefrom. The world therefore could neither increase nor diminish, nor further grow old. (As proof of this we may) consider how, from all eternity, the earth constantly preserves the same shape and mass; similarly, the air never diminishes, any more than the water. The changes within them do not affect the universal living Organism. Even we human beings subsist a long while, in spite of the perpetual change of our constituent parts, and though some of these parts even issue from the body. So much the more will the world's nature, from which nothing issues, sufficiently harmonize with the nature of the universal Soul to form along with her an organism which ever remains the same, and subsists for ever.