Which layer of the Earth is liquid and primarily composed of iron and nickel?

The outer core of the Earth is indeed liquid and is primarily composed of iron and nickel. This layer lies beneath the solid mantle and above the solid inner core. The outer core is crucial for generating the Earth's magnetic field through the movement of its molten metal, a process known as the geodynamo. The temperatures within the outer core are extremely high, causing the iron and nickel to remain in a liquid state despite the pressure from the layers above.

In contrast, the crust is the outermost layer of the Earth and is solid, consisting of various rocks and minerals. The mantle, while mostly solid, has some regions called the asthenosphere where partial melting can occur, but it is primarily composed of silicate minerals. The inner core, located at the center of the Earth, is solid due to the immense pressures that keep the metals in a solid state despite its high temperatures.

Thus, the outer core is characterized by its liquid state and composition, making it distinct from the other layers of the Earth.