Here's why:

* Earth's Core: The Earth's core is primarily composed of iron, making up about 32% of the Earth's total mass.

* Mantle: While the mantle is primarily composed of silicate minerals, it also contains a significant amount of iron.

* Crust: The Earth's crust contains less iron than the core and mantle, but it still contributes to the overall abundance of this element.

While oxygen is the most abundant element in the Earth's crust, the Earth as a whole contains more iron.