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Layers of the Earth

Geography · Year 3–Year 6

Tap a layer to name it, then look at the crust close up.

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About the earth layers

A cross-section of the Earth with the four layers to name. Tap one and the board says what it is called and what it is made of, or turn every label on for the version of the lesson that is not a quiz.

The mantle and the outer core turn over while you watch, because that is what they do. The mantle is solid rock that moves very slowly, which is the thing a class most often has the wrong way round: the layer that is liquid is the outer core, and it is the moving iron in it that gives the Earth its magnetic field. Stop the movement for a quiet classroom, and it stops on its own for anyone who has asked for no animation.

The mantle and both cores are drawn where they really are: the boundaries are the real depths, 2,900km and 5,150km, divided by the real radius. The crust is not. To scale it would be about a fiftieth of the radius, which on a whiteboard is a pencil line nobody could tap, so it is drawn roughly sixteen times thicker than it is.

Which is what the second diagram is for. It is the top 60km at a scale where the crust IS to scale: 7km of rock under the sea, 35km under the land, and thickest of all under the mountains. Sixty kilometres is about one per cent of the way to the middle, so the whole of that picture is the very edge of the ring on the first one. Asking a class to put the two together is the best question the tool can be asked.

Good before a lesson on volcanoes or earthquakes, where the point is that the crust is a thin shell on top of something that moves.

How to use it on your whiteboard

  1. 1Tap a layer to name it and see what it is made of.
  2. 2Tap Next to go through them from the outside in.
  3. 3Switch to Crust for the close up, where the crust is drawn to scale.
  4. 4Turn Labels on to show every part at once.
  5. 5Tap Stop to hold the rock still, and Clear to ask the class again.

Questions

Is the mantle liquid?
No. The mantle is solid rock, and it moves, very slowly. The liquid layer is the outer core, which is molten iron. The inner core is solid iron, kept solid by the pressure on it.
Is the diagram to scale?
Below the crust, yes: the mantle and core boundaries are the real depths over the real radius. The crust is drawn about sixteen times too thick, because to scale it is a hairline. The second diagram is the close up where it is to scale.
Why is the mantle moving?
Because it does. It is solid rock, but it is hot enough to creep, and it turns over in slow cells that carry the plates about on top of it. The outer core turns over too, and that is where the magnetic field comes from.
How hot is the inner core?
About 5,500 degrees, which is roughly the temperature of the surface of the Sun.