Final answer:
Iron (Fe) makes up approximately 85% of the Earth's core by mass, and the core constitutes about 16% of the planet's total volume. Iron is also a significant element in the Earth's mantle and crust, though not as predominant as in the core.
Step-by-step explanation:
The percentage of Iron (Fe) in the composition of the layers that make up the Earth varies by layer. The Earth's core, which includes the inner and outer core, comprises about 16% of the planet's total volume and is thought to be composed of approximately 85% iron with nickel making up much of the remaining 15%. The Earth's crust, however, contains iron as one of the eight most abundant elements; although it is not the majority element, iron does play a significant role in the crust's composition as well.
The Earth's mantle, which lies above the core, has a thickness of about 2,900 km and contains more iron and magnesium relative to the crust. Therefore, while iron is a major component, especially in the core, the percentage of iron in the Earth's entire structure is not uniformly distributed. Iron's presence is vital in both the composition of the core and mantle and contributes to the Earth's overall density.