Plural of atoll; ring-shaped coral reefs that form islands with a lagoon in the center.
From Maldivian 'atolu' (borrowed into English through Dutch and Portuguese traders). Atolls are coral reef formations that grow around subsiding islands, creating distinctive circular shapes with enclosed lagoons.
Atolls are natural masterpieces of circular geometry—Darwin observed them while traveling and theorized that as islands slowly sink over millions of years, coral keeps growing upward, gradually forming these perfect rings with lagoons inside.
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