Build your castles on the sand and they might be washed away. Water creeps or washes in. It sinks down under the sand. The beach quakes. The rocks fall….
What is sand? Silica, ground up rock and shells. Sand can be melted into glass, a solid once liquid. Fused in heat either through vulcanism, lightening (did you know when lightening strikes damp sand it can melt a branching path through it, like plant roots?). Humans also build kilns and create glass to be blown or fused or slumped.
The sea washes or crashes in to a beach. Longshore drift pushes sand and rock sideways and along a coast. In a severe storm sand can be stripped off a beach completely, and yet it can equally be washed back again.
The world warms, water rises, sand washes away, cliffs crumble, castles crumble.
Life changes and evolves.