Virginia Arnold, age 12, of Dallas, Texas, or her question:

How is soil formed on a coral island?

The solid mass of coral was a‑building for millions of years, At last it breaks the surface of the warm ocean. Twice a day, the tide pounds and floods it ‑ but only for a time, At last the mound of coral is big enough to stand above high tide. It is an island come to stay.

Soil is powdered rock mixed with chemicals from the decayed remains of plants and animals. Billions of sea plants and animals have lived and died in the pores and crevices of the coral. It is already rich with chemicals. The winds bring seeds, tiny spores and bacteria. They live and die, adding more chemicals to the coral. Waves, winds and rain chip and chomp the surface coral to powder. Birds arrive to look over the new island.

The tide washes in floating sticks and logs. There may be insects and even small animals adrift on the flotsom. They come to stay. A coconut may float in. If so, it is sure to find rich soil in which to grow. In ten to fifteen years, the brand new island is clothed with plants and maybe populated with animals.