The Great Barrier Reef of Australia passed away in 2016 after a long illness. It was 25 million years old.For most of its life, the reef was the world’s largest living structure, and the only one visible from space. It was 1,400 miles long, with 2,900 individual reefs and 1,050 islands. In total area, it was larger than the United Kingdom, and it contained more biodiversity than all of Europe combined. It harbored 1,625 species of fish, 3,000 species of mollusk, 450 species of coral, 220 species of birds, and 30 species of whales and dolphins. Among its many other achievements, the reef was home to one of the world’s largest populations of dugong and the largest breeding ground of green turtles. The reef was born on the eastern coast of the continent of Australia during the Miocene epoch. Its first 24.99 million years were seemingly happy ones, marked by overall growth. It was formed by corals, which are tiny anemone-like animals that secrete shell to form colonies of millions of individuals. Its complex, sheltered structure came to comprise the most important habitat in the ocean. As sea levels rose and fell through the ages, the reef built itself into a vast labyrinth of shallow-water reefs and atolls extending 140 miles off the Australian coast and ending in an outer wall that plunged half a mile into the abyss. With such extraordinary diversity of life and landscape, it provided some of the most thrilling marine adventures on earth to humans who visited. Its otherworldly colors and patterns will be sorely missed.