Which two layers of earth are mainly composed of iron and nickel

The inner and outer cores.

Explanation:

The Earth has four layers:

The crust: It's only 8 kilometers thick under the oceans and 32 kilometers thick under the continents, it's the thinner of all layers.   This layer is broken into many pieces called plates. When plates interact an Earthquake occurs.The mantle is the largest layer of the Earth with 1800 miles thick, it is composed of very hot (temperature from 1600 to 4000 degrees Fahrenheit), dense rock.  Outer core: Is about 1400 miles thick and its temperature goes from 4000 to 9000 degrees F melting the metals in it (nickel and iron), keeping them in liquid state. Inner core: The temperatures and pressures in this layer are so great that the metals in it are squeezed together, forming a nickel-iron alloy, forced to vibrate in place as a solid. This layer is 800 miles thick and its temperatures reach 9000 degrees F.

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