Key Stage 3 geography · Physical geography

KS3 plate tectonics and geological time: a parent guide

Plate tectonics explains why the Earth has mountains, volcanoes and earthquakes, and why they appear in some places and not others. In Key Stage 3, children learn that the Earth is about 4.5 billion years old, that its outer shell is broken into slowly moving plates, and that most of the planet’s dramatic landforms and hazards form where those plates meet. They also learn to think about time on a scale far beyond human lives.

Plate tectonics and geological time, explained

The National Curriculum lists geological timescales and plate tectonics as the first of four areas of physical geography for Key Stage 3, alongside rocks, weathering and soils, weather and climate, and glaciation, hydrology and coasts. Pupils are meant to learn key processes through detailed place-based exemplars at a variety of scales, so schools choose their own examples. Common choices include the 2011 Tōhoku earthquake and tsunami in Japan, the 2015 earthquake in Nepal and the volcanoes of Iceland, such as the 2010 eruption of Eyjafjallajökull. The aim is to understand how geographical processes interact to create landscapes that change over time.

Geological time is the first idea. The Earth formed about 4.5 billion years ago. Simple life appeared very early, dinosaurs lived from about 230 to 66 million years ago, and modern humans have existed for only around 300,000 years. Teachers often squeeze the whole of time into a single day or a long strip of paper to show how short human history is. The Earth itself has layers. A thin, solid crust sits on a thick mantle of hot rock that is solid but flows very slowly, around a liquid outer core and a solid inner core of iron and nickel. Many children believe the mantle is a sea of liquid magma, but magma forms only in certain places, such as beneath volcanoes.

The crust and the top of the mantle are broken into plates, which move a few centimetres a year, about the speed that fingernails grow. Where plates pull apart, as along the Mid-Atlantic Ridge and the East African Rift, new crust forms and volcanoes can erupt. Where an oceanic plate meets a continental plate, the denser oceanic plate sinks beneath the other in a process called subduction, creating a deep ocean trench, strong earthquakes and a chain of volcanoes. Where two continental plates collide, neither sinks easily, so the crust crumples into fold mountains, as in the Himalayas. Where plates slide past one another, as along the San Andreas Fault in California, stress builds up and is released as earthquakes. Many schools teach that slow convection currents in the mantle move the plates. Scientists now think the pull of cold, dense plate edges sinking into the mantle is one of the most important forces, working alongside those currents.

Evidence built the theory. In the early twentieth century, Alfred Wegener noticed that the coasts of South America and Africa fit together, and that matching rocks and fossils occur on different continents. Later, maps of the sea floor and patterns in magnetic rocks on either side of ocean ridges showed that new crust is being created and that the sea floor is spreading. Between about 300 and 200 million years ago the continents were joined in one landmass, Pangaea, which then slowly broke apart. Britain once lay near the Equator, which is why it has coal made from ancient tropical forests. Children also learn that earthquakes cannot be predicted, although volcanoes can often be monitored, and that preparation, such as earthquake-resistant buildings and warning systems, saves lives.

Words your child will hear

Crust: The thin, solid outer layer of the Earth. It is thinner under the oceans than under the continents.
Mantle: The thick layer of hot, solid rock below the crust that flows extremely slowly.
Plate boundary: The line where two tectonic plates meet, where most earthquakes and volcanoes occur.
Subduction: One plate sinking beneath another where they collide, usually a denser ocean plate going under a continental plate.
Magma: Molten rock beneath the surface. When it reaches the surface it is called lava.
Epicentre: The point on the surface directly above the place underground where an earthquake starts.
Fault: A crack in the crust along which rocks have moved, often the source of earthquakes.

What the National Curriculum says

The programme of study for Key Stage 3 says:

Pupils should be taught to understand, through the use of detailed place-based exemplars at a variety of scales, the key processes in physical and human geography
Physical geography relating to: geological timescales and plate tectonics; rocks, weathering and soils; weather and climate, including the change in climate from the Ice Age to the present; and glaciation, hydrology and coasts
Pupils should understand how geographical processes interact to create distinctive human and physical landscapes that change over time.

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

Try it: explaining a pattern with plate tectonics

Explain why there are earthquakes and volcanoes along the west coast of South America, and why the Andes mountains are there.

Identify the plates. The Nazca Plate lies under the Pacific Ocean, west of South America, and the South American Plate carries the continent. Look at the boundary on a map of plates.
Say how they move. The Nazca Plate is moving east, towards South America, by several centimetres a year. This is a destructive (convergent) boundary.
Explain what happens. The Nazca Plate is oceanic, so it is thinner and denser than the continental plate, and it is forced down beneath it in subduction. This forms a deep ocean trench along the coast. The plates catch on each other, stress builds up, and when they suddenly slip the result is an earthquake, such as the great earthquake in southern Chile in 1960, the largest ever recorded.
Link to volcanoes. As the sinking plate descends it heats up and releases water, which causes the mantle above to melt. The magma rises and erupts through the crust, forming a chain of volcanoes.
Link to the mountains. The pushing of the two plates crumples and lifts the edge of the continent, and the volcanoes add to its height. Over millions of years, this has built the Andes.

Along the west coast of South America, the dense Nazca Plate is being pushed beneath the South American Plate. The sinking plate causes deep trenches and earthquakes, and the melted rock rises to feed volcanoes, while the squeezing and uplift build the Andes. All of this happens because two plates are moving towards each other.

Common mistakes and how to help

Thinking the mantle is liquid and the continents float on a sea of magma

Diagrams and volcano pictures show glowing lava, so children assume the whole interior is liquid. In fact, the mantle is solid rock that creeps very slowly, and only the outer core is liquid.

What helps: Use the idea of very thick toffee or glacier ice: solid, but able to flow over long periods of time. Point out that magma exists only in pockets.

Using “plate” and “continent” to mean the same thing

Maps often show continents and plates in similar shapes, but plates include both continental and ocean floor, and the boundaries do not follow coastlines. The Pacific Plate is almost all ocean.

What helps: Compare a map of continents with a map of plates and draw attention to where the plate boundaries are in the middle of oceans.

Believing dinosaurs and humans lived at the same time

Films and cartoons show them together, and “long ago” blurs very different time periods into one.

What helps: Make a physical timeline and see how far apart they sit. The dinosaurs died out about 66 million years ago, apart from the birds that descended from them, and modern humans appeared about 300,000 years ago.

Thinking earthquakes and volcanoes happen only at plate boundaries, and that earthquakes can be predicted

Most do occur at boundaries, but not all. Hawaii’s volcanoes sit over a hotspot in the middle of a plate, and the UK has small earthquakes. Scientists can show where earthquakes are likely, but not when.

What helps: Ask what it means to say a place is high risk, and discuss how preparation, such as buildings and drills, is different from prediction.

How to help at home

String timeline of the Earth. Cut about 4.5 metres of string or ribbon and let 1 millimetre stand for a million years. Mark when the dinosaurs died out (66 millimetres from the end) and when modern humans appeared, which is only about a third of a millimetre from the end, roughly the width of a pencil line.
Fit the continents together. Trace South America and Africa from an atlas, cut them out and see how the coastlines fit. Discuss what other evidence, such as matching fossils, supports the idea.
Crumple a mountain range. Lay a towel or tablecloth on a table and push the two ends slowly towards each other. Watch how the folds rise, then connect it with the Himalayas and the Alps.
Map the Ring of Fire. In an atlas, mark the locations of recent earthquakes and major volcanoes with dots. The pattern around the Pacific Ocean makes the plate boundaries visible.
Hunt for ancient rocks. On a walk or museum visit, look at building stones, pebbles or fossils, keeping well away from cliff edges and the foot of cliffs. Ask how old your child thinks they are, and which sea or climate might have created them.

Builds on

Key Stage 2: Climate zones, biomes and vegetation belts
Key Stage 2: Rivers and the water cycle
Key Stage 2: Mountains
Key Stage 2: Volcanoes and earthquakes
Key Stage 2: Settlements and land use
Key Stage 2: Economic activity and trade
Key Stage 2: Natural resources