Here's why:
* Deepest Layers: The Earth's deepest layers are the mantle and the core.
* Mantle Composition: The mantle is primarily composed of ultramafic rocks, which are very rich in magnesium and iron.
* Magma Formation: Extreme heat and pressure in the mantle cause rocks to melt, forming magma.
* Crystallization: As magma cools and solidifies, it forms igneous rocks.
Ultramafic rocks are the most common type of rock found deep within the Earth's mantle. They are generally dark-colored and have a high density. Examples of ultramafic rocks include peridotite and dunite.
While sedimentary and metamorphic rocks can also exist deep within the Earth, they are less common than igneous rocks in those depths.
