Its a cycle of time. It starts with the creation of the mortal realm and presumably ends once mortals once again achieve godhood.

Ah, I see. I wonder what "The Song Of Pelinal, V, 7" means when it states "...and he(Umaril) listed his bloodline in the Ayleidoon and spoke of his father, a god of the [previous kalpa's] World-River."

Pretty soon Akel caused Satak to bite its own heart and that was the end. The hunger, though, refused to stop, even in death, and so the First Serpent shed its skin to begin anew. As the old world died, Satakal began, and when things realized this pattern so did they realize what their part in it was. They began to take names, like Ruptga or Tuwhacca, and they strode about looking for their kin. As Satakal ate itself over and over, the strongest spirits learned to bypass the cycle by moving at strange angles.