Age
How old are today's reefs? The geological record indicates that ancestors of modern coral reef ecosystems were formed at least 240 million years ago. The coral reefs existing today began growing as early as 50 million years ago. Most established coral reefs are between 5,000 and 10,000 years old.
The longest lived coral colony on record is from a species of black coral from the genus Leiopathes that had an estimated age of 4,265 years old using radiocarbon dating methods – making it perhaps the oldest known living marine organism.
Source: National Oceanic and Atmospheric Administration