The lithosphere is broken into rigid plates that move a few centimetres a year. Slow convection currents in the hot mantle carry them, driven by Earth's inner heat: from the core below and from radioactive elements in the mantle rock itself.
Australia is moving north about 7 centimetres a year, nearly twice as fast as your fingernails grow. A whole continent. What could possibly push it?
Earth's surface is not fixed. This lesson is about the engine underneath.
Make your prediction first. Help opens once you've locked it in.
Convection is how heat moves through a fluid: the warm part rises because it is less dense, then cools and sinks. You may have met it in a pot on the stove or a heater in a room.
Follow the ringed particle (or click another). Blue is cooler, red is hotter. Watch the plates on top too.
Follow a particle round one full loop of the current.
Use the board. This ticks when you get there.
In your book: explain how Earth's inner heat makes a plate move. Use "heated", "less dense", "rises", "cools", "sinks" and "current".
Put each description with its part of the Earth.
Australia moves about 7 cm north each year. How many kilometres is that in a million years? (100,000 cm = 1 km)
Follow a particle round one loop in the heated water.
Use the board. This ticks when you get there.
Match each force to how it moves a plate.
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Students explain that the lithosphere is divided into moving plates and describe mantle convection, driven by Earth's inner heat (from the core and from radioactive decay in the mantle), as the mechanism (AC9S8U03, node 2, a hinge node). About 25 minutes.
Open the teacher guide: answers, solutions, slides and a worksheet.
A concept tutorial for introducing or revising the idea; it does not replace a convection demonstration. Set the width with ?width=minimum, typical (default) or wider.
The hinge risk is plate movement with no mechanism: without convection, boundary features (nodes 3 to 5) look arbitrary.
Assumed: convection, and density from Year 7 (less dense rises). These tutorials teach convection in Year 9 (Heat transfer), so Explore opens with a one-question recap (warm fluid rises because it is less dense). If the class has not met convection, demonstrate it first (see In class, below).
Model notes, worth saying aloud: the board draws the mantle as moving particles, but the real mantle is solid rock that flows over millions of years. In the model hot particles are pushed up directly; real hot rock rises because it is less dense. The plates on top move with the surface flow.
Giving a mechanism: mantle convection carries the plates. When a student says heat rises, ask what is actually moving up on the board.
Stretch: The Australian continent's centre has some of the oldest, most stable rock on Earth. Use the board to suggest why the middle of a plate is quieter than its edges.
Support: Give a four-box cycle diagram (heated, rises, cools, sinks) to fill in while watching the board.
Next: what happens where plates meet: divergent (node 3), convergent (node 4) and transform (node 5) boundaries.
In class: a beaker of water heated from one side with a few potassium permanganate crystals or food colouring, and a raft of paper on top.