What characterizes the outer core of the Earth?

The outer core of the Earth is characterized as a liquid layer that surrounds the solid inner core. This layer is primarily composed of molten iron and nickel, which allows it to maintain a fluid state. The movement of this molten metal is also responsible for generating Earth’s magnetic field through the geodynamo effect. The liquid state is crucial as it facilitates the convection currents that contribute to the magnetic field dynamics.

In contrast, the other options do not accurately depict the outer core. It is not solid, nor does it contain mantle material, as the mantle lies above the outer core. Additionally, the outer core is not the coolest part of the Earth's interior; rather, it is significantly hotter than both the crust and mantle, with temperatures reaching upwards of 4,000 to 5,000 degrees Celsius. This high temperature is indicative of its molten state, further confirming its characterization as a liquid layer surrounding the inner core.