You are sailing the ocean and come across an atoll. What can you predict about the origin of the atoll?

a) It was along a mid-ocean ridge

b) It started as a fringing reef

c) It was built up from a carbonate platform

d) It started as an EEZ methane hydrate

b) It started as a fringing reef

Explanation:

When an island (basically a seamount or eroded volcano) that is formed on a caldera and which is surrounded by fringing reefs starts to sink or the sea level starts to rise gradually and engulf it, i. e. when the fringing reefs starts to grow it gradually forms an atoll.

It is basically a coral reef encircling a logoon. Coral starts to grow and build a fringing reef and later this barrier reef forms the atoll, which encircles a lagoon.