Final answer:
The first step of the Darwin-Dana-Daly theory of coral atoll formation is the gradual subsidence of a volcanic island into the sea. This process occurs over millions of years, and as the island sinks, the coral reef grows upward to stay near the water's surface. Eventually, the island completely sinks, leaving behind a circular coral reef called an atoll.
Step-by-step explanation:
The first step of the Darwin-Dana-Daly theory of coral atoll formation is the gradual subsidence of a volcanic island into the sea.
This process occurs over millions of years as the volcanic island sinks beneath the ocean surface.
As the island subsides, the coral reef that was previously fringing the island grows upward to stay near the water's surface.
This creates a ring-shaped coral reef called a barrier reef.
Eventually, the island sinks completely below the water, leaving behind a circular coral reef called an atoll.