Turns out coral islands can form just from water currents, which totally upends Darwin’s old theory.
March 19, 2026
Original Paper
Hydrodynamics shapes annularity in coral reefs via scale-free growth processes
arXiv · 2603.16933
The Takeaway
Since the 1840s, we believed ring-shaped coral reefs only formed as volcanoes sank into the ocean. Researchers have discovered that water flow creates these identical 'rings' across all sizes, meaning the ocean itself can sculpt reefs without needing a sinking island.
From the abstract
Atolls are traditionally explained as the result of coral reefs accreting around volcanic islands followed by gradual subsidence, yielding a hollow, ring-shaped rim that can extend for kilometres. However, satellite imagery shows that similar annular outlines also appear in much smaller patch reefs, where atoll-forming geological pathways do not apply. In some systems, small annular patches occur within the lagoons of larger atolls, producing nested ring-like patterns. The recurrence of annulari