So scientists used to think that these little larvae, these tiny dots that you see here, were helpless, randomly pushed around by wind and waves and currents.

从前科学家认为这些小幼虫，如图所示的小点，会随风、海浪、水流肆意飘摇。

It was probably buried under a deep layer of sand without a lot of oxygen, and waves and currents apparently shifted that sand recently so the diver could see it.

它可能被埋在一层没有很多氧气的沙子下面，最近海浪和洋流显然改变了沙子的位置，所以潜水员可以看到它。

Over thousands and thousands of years, the paths of rivers sweep up and down the coast, dropping off piles of sand to be spread by waves and currents into smooth sandy beaches.

千百年来，河流的路径在海岸上扫荡，落下一堆沙子，被海浪和海流铺成光滑的沙滩。