This allusion is from Stories of the Immortals. Female immortal Magu once said to male immortal Wang Yuan, "Since we first got to know each other, I have thrice seen the East Sea change into mulberry orchards. When I went to Penglai last time, I saw the sea had become shallow again, the depth being only half of what it usually is. I am afraid it will soon become mulberry orchards again."

Wang Yuan answered, "I have heard from a sage that dust is going to replace the sea."

This phrase is used to refer to the upheavals and great changes in the world and in human lives, or the passing of time.