How do atolls form their ring shape?
Show answer & explanation
Answer: Coral grows around sinking island
Ocean currents circle — Wrong. Currents don't shape atolls. Ring shape forms as coral grows outward around a sinking volcanic island center.
Coral grows around sinking island ✓ — Correct! Atolls form through subsidence. A volcanic island emerges, coral grows fringing the shore. As the island slowly sinks (plate movement), coral keeps growing upward, forming a barrier reef. Eventually the island sinks completely, leaving a ring-shaped reef around a lagoon. Darwin predicted this mechanism!
Underwater meteor impacts — Wrong. Atolls aren't impact craters. They're coral reefs that grew around volcanic islands that gradually sank beneath the sea.