The earth's subsystems that played a major role in the formation of Oceania are:
1. Hydrosphere
2. Lithosphere
The lithosphere is the primary subsystem responsible for the formation of the islands in Oceania. Most of which are formed from the collision of the tectonic plates in the earth's crust while some are formed by volcanic eruptions.
The Hydrosphere is responsible for the formation of most coral islands found in this territory. A build-up of coral reefs constitutes an atoll that can be defined as an island.