Which description best defines an oceanic plate?

• A. A rigid plate forming the continents.
• B. A tectonic plate primarily composed of basalt and found beneath the ocean, thinner and denser than continental plates.
• C. A layer of molten rock within the mantle that moves slowly.
• D. The boundary where tectonic plates sink back into the mantle.

Answer: (B)

Oceanic plates are the oceanic portion of Earth's lithosphere. They are primarily composed of basalt and lie beneath the oceans, forming a thinner and denser shell than continental plates. This basaltic, oceanic lithosphere is why these plates are relatively thin and heavy compared to continental crust, and why they tend to subduct beneath lighter continental plates at convergent boundaries. The other descriptions point to continents, a mantle layer, or a boundary process, none of which define an oceanic plate itself.