Chapter 2: Problem 17

What is the difference between lithosphere and asthenosphere? Which layer is softer and flows easily? At what depth does the lithosphere-asthenosphere boundary occur? Is this above or below the Moho?

Short Answer

Expert verified

The lithosphere is the outermost rigid layer of the Earth, made up of the crust and the upper part of the mantle, while the asthenosphere is the ductile, semi-solid layer beneath it. The asthenosphere is softer and flows more easily than the lithosphere due to its partially molten state. The lithosphere-asthenosphere boundary (LAB) occurs at a depth of around 100 kilometers, although this may vary. The Mohorovičić discontinuity (Moho) lies above the LAB, marking the boundary between the Earth's crust and the upper mantle.

Step by step solution

Define Lithosphere

The lithosphere is the outermost rigid layer of the Earth, comprising of the crust and the uppermost part of the mantle. This layer is made up of tectonic plates that move and interact with each other.

Define Asthenosphere

The asthenosphere is the layer below the lithosphere, which is a more ductile and pliable region of the mantle that extends from around 100 to about 700 kilometers below the surface. It consists of partially molten, semi-solid rock material that allows for the movement of tectonic plates.

Compare Lithosphere and Asthenosphere

The main difference between lithosphere and asthenosphere is their consistency and behavior. The lithosphere is a rigid layer composed of solid rocks, while the asthenosphere is a ductile layer with semi-solid rocks that exhibit plastic properties, which means it can flow.

Identify Softer Layer and Flow Characteristics

The asthenosphere is the softer layer of the two and flows more easily than the lithosphere, due to its partially molten state and the pressure from the overlying lithosphere.

Determine Depth of Lithosphere-Asthenosphere Boundary

The lithosphere-asthenosphere boundary (LAB) occurs at a depth of around 100 kilometers below the Earth's surface. However, the depth may vary depending on various factors like the age of oceanic lithosphere, location, and tectonic activity.

Relate to the Mohorovičić Discontinuity

The Mohorovičić discontinuity (Moho) marks the boundary between the Earth's crust and the upper mantle; it lies above the lithosphere-asthenosphere boundary. The depth of the Moho varies between 5 kilometers beneath oceanic crust to up to 70 kilometers beneath continental crust. Since the lithosphere also includes the uppermost part of the mantle, the lithosphere-asthenosphere boundary is deeper than the Moho.

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What is the difference between lithosphere and asthenosphere? Which layer is softer and flows easily? At what depth does the lithosphere-asthenosphere boundary occur? Is this above or below the Moho?

Short Answer

Step by step solution

Define Lithosphere

Define Asthenosphere

Compare Lithosphere and Asthenosphere

Identify Softer Layer and Flow Characteristics

Determine Depth of Lithosphere-Asthenosphere Boundary

Relate to the Mohorovičić Discontinuity

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