Lessons · Teaching · inside the Earth, and why it moves
The surface is broken into plates and they are moving now
The Earth has a thin crust, a thick mantle that flows very slowly, and a core. The crust is broken into plates that move a few centimetres a year. Earthquakes and volcanoes occur mostly where plates meet, which is why they are not spread evenly.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
In beta. This lesson was written for Hone and has not yet been checked by a state certification officer. Practice material, not professional advice. What that means.
What it is for
The evidence is the lesson: the coastlines fit, the same fossils appear on both sides of an ocean, and earthquakes cluster in lines. A class asked to explain that pattern can reason their way to plates, and that is a far better hour than being told.
How to think about it
Start from the map, not the mechanism. Ask why earthquakes are in lines rather than everywhere, and why identical fossils are found on separated continents. Then name what would explain it, and only then describe the layers underneath.
Worked example
Crust is thin and solid; the mantle beneath flows extremely slowly; the core is the centreThree layers, and the middle one is what carries the plates.
Plates move a few centimetres a year, about as fast as a fingernail growsSlow, and never stopped.
Plates pulling apart make new crust; pushing together builds mountains or subducts one plateTwo boundaries, two very different landscapes.
Earthquakes and volcanoes cluster along boundaries, which is why the map has lines on itThe pattern is the evidence, and it came before the explanation historically too.
Your turn
Name the layer beneath the crust that the plates move on.
The plates move on the
Solve one, graded on the server
The trap
Describing the mantle as liquid. It is solid rock that deforms and flows over very long timescales. Calling it liquid makes the crust sound like a raft on a sea, which misleads about almost everything that follows.