What is the outer core primarily made of?

The outer core of the Earth is primarily composed of liquid iron and nickel. This layer lies beneath the mantle and surrounds the inner core, which is solid. The high temperatures and pressures in the Earth's interior cause the iron and nickel in the outer core to remain in a liquid state. This fluid movement of molten metals is crucial because it generates the Earth's magnetic field through the geodynamo process. In contrast, the inner core is solid due to even greater pressures that prevent the metals from remaining in a liquid form.

The other choices involve materials that do not accurately describe the composition of the outer core. Solid iron and nickel would pertain to the inner core, while soft, slightly molten rock would be more relevant to the mantle. Copper and aluminum are not significant components of the Earth's core, as they are primarily found in the crust rather than in the deep interior.