Sweet mystery of life

Where did the white sand on our beaches come from? That's easy. From the erosion of the islands. But wait. The islands are themselves made of heaped up sand, consolidated into a soft white rock. Drive up to the places where a road cuts through the ridges and see the layers, blown this way and that by Pleistocene winds. So where did the original sand come from?

I have seen at least part of the answer. When we snorkel in the shallows we cruise through algal gardens, colonies of little plants that have hardly changed since the dawn of time. One of these, Halimeda, a green alga, incorporates into its tissues grains of calcium carbonate extracted from sea water. When it dies it leaves behind -- you guessed it -- sand.

Give me Halimeda and a billion years or so, and I'll give you an island. It's a lovely story, and half of Americans refuse to believe it.