Self-sustenance of nature (Aurelius)

Nature has no door to sweep things out of. But the wonderful thing about its workmanship is how, faced with that limitation, it takes everything within it that seems broken, old and useless, transforms it into itself, and makes new things from it, so that it doesn't need material from any outside source, or anywhere to dispose of what's left over. It relies on itself for all it needs: space, material, and labor.

-- Marcus Aurelius, from the Meditations, sect. 8.50