The Earth's tectonic plates
The crust is not one solid shell — it is cracked into giant moving slabs.
In Grade 6 you learned the Earth has four layers, with a thin solid crust on the outside. This year comes the surprising part: that crust is not one piece. It is cracked into about a dozen huge slabs called tectonic plates.
The plates sit on top of the mantle. The mantle is solid rock, but it is so hot that it can flow very slowly, like extremely thick treacle. Slow movement inside the mantle drags the plates along with it.
How fast do plates move? Only a few centimetres each year — about the speed your fingernails grow. It feels like nothing, but over millions of years it adds up to thousands of kilometres. Continents that are now far apart were once joined together.
- Tectonic plates are huge slabs that make up the Earth's crust.
- They float on the slowly flowing mantle beneath.
- They move only a few centimetres per year.
- Over millions of years, this slow drift moves whole continents.
The places where two plates meet are called plate boundaries. As you will see, almost all of the Earth's most dramatic events happen there.
- The crust is broken into about a dozen tectonic plates.
- Plates rest on, and are moved by, the slowly flowing mantle.
- Plates move a few centimetres a year — like fingernail growth.
- Over millions of years, plate movement reshapes the whole planet.