The Great Barrier Reef is the largest living structure on Earth, built by tiny coral animals.

The longer version

Coral animals build hard skeletons around themselves, and each generation adds to the framework left by the last. Over long periods the accumulated limestone becomes large enough to be seen from orbit. The animals live together with algae that supply food through photosynthesis, which is why reefs need clear, sunlit water.

Such structures grow only within a narrow temperature range. When water stays too warm, corals expel their algae and turn pale, a process called bleaching. Reefs shelter a large share of ocean species and protect coastlines from wave energy, which makes their condition closely watched.

Where this entry sits

These facts wander across maps, borders, deserts, rivers, mountains, and the extreme corners of the natural world. Each one is short and self-contained, offering a small surprise about places you may never visit rather than anything you actually need. The full list sits on the Geography page, where every entry is listed in order.