The composition of Earth's layers changes significantly with depth, transitioning from lighter silicate rocks at the surface to denser metals at the center.

Crust

The outermost layer, the crust, ranges from 5 to 70 kilometers deep. It consists mainly of lighter silicate rocks:

• Oceanic crust (5-10 km thick) is dense and mafic-rich, composed largely of iron-magnesium silicate minerals like basalt.
• Continental crust is thicker and less dense, composed mostly of felsic rocks rich in feldspar and quartz (aluminum silicate).

Mantle

Beneath the crust lies the mantle, extending to about 2,890 km depth:

• Composed of silicate rocks richer in iron and magnesium than the crust.
• It is subdivided into the upper and lower mantle, with the upper mantle partly solid but able to flow slowly.
• The mantle rocks are denser and hotter with depth, behaving plastically under high pressure and temperature.

Outer Core

Beneath the mantle is the outer core, extending from 2,890 km to about 5,150 km depth:

• Composed mostly of liquid iron and nickel, making it the only liquid layer of the Earth.
• Responsible for Earth's magnetic field due to convective flows.

Inner Core

The innermost layer, the inner core, extends from about 5,150 km to Earth's center at 6,371 km:

• Solid metal ball composed primarily of iron and nickel.
• Extremely dense, hot (around 5,400 °C), and under immense pressure.

In summary, Earth's composition shifts from lighter, silicate-rich rocks in the crust and mantle to heavy metallic iron-nickel alloys in the core, with physical states changing from solid in crust and mantle, to liquid in the outer core, and solid again in the inner core. This gradual increase in density, temperature, and pressure with depth strongly influences the behavior and state of each layer.