100 million years from now; the Earth warms up
The ice age has ended. The ice has melted, and sea levels have risen 100 metres, changing the shape of the coastlines. The continents are still moving. Australia has collided with Asia, pushing up a huge mountain range. Antarctica has moved north, warming up and supporting a huge, lush forest. Part of Africa has split off and become fused to the tip of Asia.
Vast tracts of Russia are under water. Shallow seas spread across Northern Europe and Asia, with rocky islands - mountain peaks not yet covered by water.
The seas are rich in nutrients and in bright sunlight, ideal conditions for reefs to form. The calcareous skeletons of reef organisms make a solid foundation colonised by more reef plants and animals.
The corals are extinct. The reefs are built by red algae; they photosynthesise vigorously in the light. The red algae offer browsing reef animals a protein meal; and in eating this, the animal carries away the algae's sticky spores.