Many corals secrete an exoskeleton that builds up to become a coral reef.
Australia's coral reefs, including the great barrier reef, are no exception.
The great barrier reef was formed by exoskeletons.
What was formed by exoskeletons?

  - heat produced
  - remains of prehistoric life
  - layers of fat
  - The area was once underwater
  - the Great Barrier Reef
  - the body's largest organ
  - sedimentary rocks
  - it keeps an organism warm