Ocean crust is denser than continental crust because it contains more of these three elements:

1. Iron (Fe): Iron is a heavier element than the common elements in continental crust like silicon and aluminum.

2. Magnesium (Mg): Magnesium is also heavier than silicon and aluminum.

3. Calcium (Ca): Calcium is heavier than silicon and aluminum, though less so than iron and magnesium.

These heavier elements contribute to the higher density of ocean crust compared to continental crust.