Req 7b — Build a Coral Reef Model

This option is about slow change over a very long time. Your model should show how a coral reef can begin around a volcanic island and end up as a ring-shaped atoll after the island sinks or erodes away.

Darwin’s Basic Idea

Charles Darwin proposed that coral reefs can grow upward while the volcanic island beneath them slowly subsides. In his model:

1. a volcanic island rises above sea level
2. corals grow around the shore, forming a fringing reef
3. the island slowly sinks, but the reef keeps growing upward, forming a barrier reef with a lagoon between reef and island
4. eventually the island disappears below sea level, leaving a ring-shaped atoll around a lagoon

The key idea is that reef growth and island subsidence happen together over time.

What Your Model Series Should Show

Instead of one model, think of this as three stages.

Stage 1: Fringing reef

Show coral growing close to the shoreline of the volcanic island.

Stage 2: Barrier reef

Show the island lower than before, with a wider lagoon between the island and reef.

Stage 3: Atoll

Show the island gone from above sea level, leaving a reef ring and central lagoon.

Building Tips

Clay works well because you can shape the island and reef line clearly. A board base helps keep each stage stable. Use different colors for land, reef, and water so your counselor can see the transition quickly.

What to Explain When You Present It

Your counselor will likely care as much about your explanation as the model itself. Be ready to say:

• why coral reefs start near shallow sunlit water
• why the reef can keep growing upward
• why the lagoon becomes more obvious in the barrier reef stage
• why the final atoll can remain after the island is gone from view

Next, the focus shifts from long-term reef growth to short-term measurements you can record and graph.