Final answer:
Elements not found in the Earth's outermost layer, such as iron and nickel, are typically found in the Earth's interior, including the mantle and core, due to the differences in formation conditions and pressures.
Step-by-step explanation:
The elements not found in the Earth's outermost layer, which includes the crust and atmosphere, are generally located in the Earth's interior, which is comprised of the mantle and core. The outermost layer is dominated by elements like oxygen and silicon, making up the majority of the crust's composition, while the interior contains elements such as iron and nickel.
The Earth's mantle, for example, has a significantly higher concentration of iron and magnesium compared to the crust. Understanding the composition of different layers of Earth is critical when studying the planet's geology and the distribution of elements within it.