Final answer:
The primary Earth sphere that interacts with oceans during beach erosion is the hydrosphere.
Step-by-step explanation:
The primary Earth sphere that primarily interacts with oceans during beach erosion is the hydrosphere. Beach erosion is caused by the movement of water, specifically waves, which can wear away the Earth's surface over time. The hydrosphere, which includes all the water on Earth such as oceans, lakes, and rivers, is responsible for this erosion process.