What is the outermost solid surface of the Earth beneath ocean floor sediments, composed primarily of basalt?

• A. Continental Crust
• B. Core
• C. Oceanic Crust
• D. Mantle

Answer: (C)

The outermost solid surface beneath ocean floor sediments is the oceanic crust. Oceanic crust is a relatively thin, dense shell that sits under the ocean basins and is largely made of basalt, a dark, mafic rock that forms from magma at mid-ocean ridges and crystallizes as lava erupts and spreads. Beneath this crust lies the mantle, made mostly of peridotite, and far deeper is the core. Continental crust, in contrast, is thicker and composed mainly of granitic rocks. So the basalt-rich layer right under the sediments is the oceanic crust.