General Knowledge
What is the Great Barrier Reef made of?
- Coral
- Rock
- Sand
The answer is Coral. The world's largest living structure.
Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.
Wikipedia · Coral