Inside the Earth and the theory of plate tectonics
The ground under your feet is drifting a few centimetres a year, about the speed your fingernails grow. That slow movement is the reason mountains exist, why Iceland is splitting apart, and why Japan practises earthquake drills every year.
Part of your national curriculum
- Human and physical geography: Understand how geographical processes interact to create distinctive human and physical landscapes that change over time
- Human and physical geography: Understand tectonic processes and hazards, including earthquakes and volcanic activity
Lesson overview
What you'll learn in this lesson
Describe the structure of the Earth and explain what drives plate movement.
Key learning points
- • The layers
- • What makes plates move
- • Evidence that plates move
- • The pattern of hazards
This lesson at a glance
- 25 minutes
- 21 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 21
Visual introductionPicture this
Inside the Earth and the theory of plate tectonics
The ground under your feet is drifting a few centimetres a year, about the speed your fingernails grow. That slow movement is the reason mountains exist, why Iceland is splitting apart, and why Japan practises earthquake drills every year.
In a nutshell
Describe the structure of the Earth and explain what drives plate movement.
Learning cycle
Part 2 of 21
Learning cycle 1 of 2
Part 1 · The layers
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 21
Learn
The layers
The Earth has a solid inner core of iron and nickel, a liquid outer core, a thick semi-molten mantle and a thin, brittle crust. Crust comes in two kinds. Continental crust is thick (about 30-70 km), old and low density, so it cannot sink. Oceanic crust is thin (about 5-10 km), young and denser, so it can be forced downwards. That density difference decides what happens whenever two plates meet.
Reset break
Part 4 of 21
Pause
That's sitting 1 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 21
Learn
What makes plates move
Heat from the core sets up convection in the mantle: hotter, less dense rock rises, spreads sideways and cools, then sinks again. Geologists now think the bigger force is slab pull, where a cold, dense plate sinking at a margin drags the rest of the plate along behind it, helped by ridge push as new crust slides off the raised mid-ocean ridge. Convection, slab pull and ridge push work together; you do not have to choose one.
Quick check
Part 6 of 21
Quick check
Part 7 of 21
Reset break
Part 8 of 21
Pause
That's sitting 2 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 21
Learning cycle 2 of 2
Part 2 · Evidence that plates move
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 21
Learn
Evidence that plates move
The coastlines of South America and Africa fit together. Matching rock sequences and mountain belts continue across the Atlantic, and identical fossils such as Mesosaurus, a freshwater reptile that could not swim an ocean, appear on both sides. Magnetic stripes in the sea floor either side of mid-ocean ridges are mirror images, showing new crust forming and spreading outwards. Modern GPS now measures plate movement directly.
Explore the idea
Part 11 of 21
Learn
The pattern of hazards
Plot the world's earthquakes and volcanoes on a map and they are not scattered randomly: they form narrow lines. Those lines are plate margins. The Pacific Ring of Fire, the mid-Atlantic ridge and the belt running from the Mediterranean into the Himalayas all trace boundaries. A few volcanoes, such as Hawaii, sit far from any margin over a hot spot, a plume of rising mantle that burns through the plate as it drifts.
Reset break
Part 12 of 21
Pause
That's sitting 3 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 13 of 21
Quick check
Part 14 of 21
Explore the idea
Part 15 of 21
Worked example
Worked answer: explain why plate movement occurs (4 marks)
Heat released in the core makes mantle rock rise, spread and sink in convection cells, which drags the plates above (1). Where a dense oceanic plate sinks at a margin, its cold weight pulls the rest of the plate down with it, called slab pull (1), and new crust at the raised ridge slides away under gravity as ridge push (1). Together these forces move plates a few centimetres each year, which is fast enough over millions of years to open oceans and build mountains (1). Notice that each mark is a linked step, not a separate fact.
Reset break
Part 16 of 21
Pause
That's sitting 4 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 17 of 21
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 18 of 21
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
That density difference decides what happens whenever two ____ meet.
Modern GPS now measures plate ____ directly.
Challenge round
Part 19 of 21
Game · Recall cards
Abrasion is…
Card 1 of 4
Mastery quiz
Part 20 of 21
Marked quiz
End of lesson quiz: Inside the Earth and the theory of plate tectonics
4 questions, marked with the reasoning shown. No timer.
1. Abrasion is…
2. Deposition happens when…
3. Attrition affects…
4. Managed retreat is…
Lesson round-up
Part 21 of 21
Lesson round-up
Ready when you are
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Ask LunaPart 1 of 21 · Watch & discover
How this is going
- Not looked at yet
Understand how geographical processes interact to create distinctive human and physical landscapes that change over time
- Not looked at yet
Understand tectonic processes and hazards, including earthquakes and volcanic activity