The outer rigid shell of the Earth is known as which term?

• A. Lithosphere
• B. Asthenosphere
• C. Mantle
• D. Core

Answer: (A)

The main idea is that the Earth’s outermost solid shell is the lithosphere. The lithosphere is the rigid, brittle layer that includes both the crust and the rigid part of the upper mantle, and it forms the tectonic plates that move as a whole over the layer beneath. This rigidity is what lets the plates behave like solid shells that can break and slide.

Below the lithosphere is the asthenosphere, a partly molten, ductile layer within the upper mantle that allows the rigid plates to move on top of it. The broader term mantle refers to the entire zone between the crust and the core, not just the outermost rigid portion, so it isn’t the precise label for the outer shell. The core sits at the center of the Earth, far from the outer shell.

So, the outer rigid shell is called the lithosphere.