Rocks in the mantle contain a higher percentage of iron and magnesium than do rocks in the crust.

Here's why:

* Crust: The crust is the outermost layer of the Earth and is primarily composed of lighter elements like silicon, oxygen, aluminum, and sodium.

* Mantle: The mantle is a thick layer beneath the crust, made up of denser, heavier minerals like olivine and pyroxene, which are rich in iron and magnesium.

This difference in composition is a key factor in understanding the Earth's structure and how it formed.