Mantle — Science definition

The thick, mostly solid layer of hot silicate rock between the crust and the core, about 2,900 km deep, that flows extremely slowly over millions of years.

Where it is taught

In use

Below the crust sits the mantle, an enormous shell of solid silicate rock almost 2,900 km thick and rich in iron and magnesium — by itself it makes up the largest share of Earth's volume.

Earth's Internal Structure

Questions using mantle

Problem 1

The mantle is about 2,900 km thick, and the outer core is about 2,200 km thick. How many km thicker is the mantle than the outer core?
Answer and explanation

700 km

2,900 − 2,200 = 700 km.

Problem 2

Which layer lets tectonic plates slide, because it can flow slowly like soft clay even though it's still part of the solid mantle?
  1. Lithosphere
  2. Asthenosphere
  3. Outer core
  4. Inner core
Answer and explanation

Asthenosphere

The asthenosphere is soft and flows slowly, letting the rigid lithosphere above it glide along on top of it.

Problem 3

A student labels crust, mantle and lithosphere as three separate non-overlapping compositional layers and calls slow mantle convection proof of liquid rock. Correct both statements.
Answer and explanation

Lithosphere is a mechanical layer including crust and rigid uppermost mantle, so it overlaps compositional categories. Most mantle is solid and can deform slowly under sustained stress; convection does not establish liquid state.

Lithosphere is a mechanical layer including crust and rigid uppermost mantle, so it overlaps compositional categories. Most mantle is solid and can deform slowly under sustained stress; convection does not establish liquid state.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 4

Which statement about the mantle is best supported?
  1. It is entirely molten rock
  2. It is solid rock that can flow very slowly
  3. It is liquid iron
  4. It is the thinnest layer
Answer and explanation

It is solid rock that can flow very slowly

The mantle is solid but deforms slowly over long timescales, which is what allows convection.

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