The Earth's plates are moving

The Earth's crust is cracked into huge slabs called tectonic plates. They move on the mantle below: hot, solid rock that flows very slowly. Plates drift a few centimetres a year. Most earthquakes and volcanoes happen where plates meet — a plate boundary.

There are three main types of boundary:

• Constructive (divergent): plates pull apart, magma rises and creates new crust — e.g. the Mid-Atlantic Ridge.
• Destructive (convergent): plates push together; the denser plate is forced down (subducted), causing volcanoes and strong earthquakes.
• Conservative (transform): plates slide past each other — no new crust, but powerful earthquakes, e.g. the San Andreas Fault.

Which boundary?

Rocks, weathering and soil

The three rock groups are igneous (cooled magma, e.g. granite), sedimentary (layers pressed together, e.g. limestone) and metamorphic (changed by heat and pressure, e.g. marble).

Rocks are slowly broken down in place by weathering. The main types are:

• Physical (mechanical): e.g. freeze-thaw — water freezes in a crack, expands and prises the rock apart.
• Chemical: e.g. slightly acidic rainwater dissolving limestone.
• Biological: e.g. plant roots or burrowing animals breaking rock up.

Weathered rock plus dead plant and animal material (organic matter) slowly builds up into soil, which supports farming and ecosystems.

Watch out — weathering vs erosion: weathering breaks rock down where it sits (no movement). Erosion is when the pieces are then worn away and carried off by a river, waves, ice or wind. Weathering first, erosion after.

Weathering or erosion?

Weather is not the same as climate

Weather is what the atmosphere is doing right now, in one place — sunny, rainy, windy, hot or cold. It changes hour to hour.

Climate is the average weather of a place measured over a long time — usually 30 years or more. The UK has a mild, wet temperate maritime climate; a desert has a hot, dry climate.

Watch out — weather vs climate: "It's freezing today, so global warming isn't real" mixes them up. One cold day is weather; a warming trend across decades is climate. You can't judge climate from a single day.

Climate has always changed

Earth's climate has shifted naturally for millions of years. During the last Ice Age, huge ice sheets covered much of Britain and northern Europe; it ended around 11,700 years ago. Natural causes include changes in the Earth's orbit, the Sun's output and big volcanic eruptions.

Since the Industrial Revolution, humans have added extra greenhouse gases — mainly carbon dioxide from burning fossil fuels and methane from farming. These trap more heat, so global temperatures are rising faster than natural change alone. This is the enhanced greenhouse effect.

Human-caused warming

What can one freezing day tell you?

What carved a V valley and a U valley?

The water cycle

The same water is recycled around the planet forever, powered by the Sun. Learn these key words:

• Evaporation — the Sun turns water in seas and lakes into water vapour.
• Transpiration — plants release water vapour from their leaves.
• Condensation — vapour cools and forms clouds.
• Precipitation — water falls as rain, snow, sleet or hail.
• Surface run-off & groundwater flow — water returns to the sea over and under the land.

Humans change the cycle: cutting down forests reduces transpiration, and covering land in concrete stops water soaking in, so more water runs off quickly — raising flood risk.

Name the process

Physical or human?

Tap whether each process or feature is a physical (natural) or human (people) part of geography.

Rivers shape the land

A river flows from its source (start, often in hills) to its mouth (where it meets the sea). Along the way it erodes (wears away), transports (carries) and deposits (drops) material — creating landforms.

• Upper course: steep and fast; erosion cuts a V-shaped valley and waterfalls.
• Middle course: the river winds in bends called meanders.
• Lower course: flat and wide; the river deposits silt, forming a flood plain.

Coasts: eroding and building

Waves attack the coast, eroding it in some places and depositing sand in others. Two key landforms:

• Where hard rock sticks out, waves erode a crack into a cave, then an arch, which collapses to leave a stack (a tall pillar of rock).
• Where the sea drops sand it carries along the coast, it builds beaches and long ridges called spits.

Ice carves the landscape

A glacier is a huge, slow-moving river of ice. In the Ice Age, glaciers ground across Britain and reshaped the land — you can still see the results today in places like the Lake District and Snowdonia.

Glaciers erode by two processes:

• Plucking: ice freezes onto rock and rips pieces away as it moves.
• Abrasion: trapped rocks scrape the ground like sandpaper.

This carves steep-sided U-shaped valleys and bowl-shaped hollows called corries. When the ice melts, it deposits the rock it carried, leaving ridges of debris called moraine.

Rivers cut V-shaped valleys; glaciers cut wide U-shaped valleys. The shape of a valley is a clue to what carved it.

Read the valley

What carved a V valley and a U valley?

What happens on the hill after heavy rain?

People and where they live

The world's population has grown past 8 billion and is still rising. People are not spread evenly: some places are densely populated (crowded, like cities), others are sparsely populated (few people, like deserts or mountains).

Urbanisation means a growing share of people living in towns and cities rather than the countryside. People move to cities (rural-to-urban migration) for jobs, education and services — these are pull factors. Things that push them away from the countryside, like few jobs, are push factors.

Fast urbanisation can create problems: overcrowding, traffic, pollution and shortages of housing — sometimes leading to informal settlements (shanty towns).

Push or pull?

How developed is a country?

Development means how wealthy, healthy and educated a country is — its quality of life. Countries are often grouped as higher income (HICs, e.g. the UK) or lower income (LICs), with many in between (NEEs — newly emerging economies, e.g. India).

Geographers measure development with indicators, such as:

• GDP per person — average wealth produced per head.
• Life expectancy — how long people typically live.
• Literacy rate — the share of adults who can read and write.
• HDI (Human Development Index) — combines income, health and education into one score.

Reasons for the development gap include history (e.g. colonialism), trade, debt, conflict and access to resources. Aid and fair trade can help narrow it.

Using the Earth's resources

A natural resource is anything useful we take from the environment. The four you should know are energy, water, food and minerals. They are spread unevenly across the world, which affects trade and wealth.

Energy resources split into two groups:

Watch out — renewable vs non-renewable: Renewable resources refill naturally and won't run out on a human timescale (sun, wind, water). Non-renewable resources are finite — once used, they're gone for millions of years (coal, oil, gas). Fossil fuels are reliable but release CO₂; renewables are cleaner but some (solar, wind) are less reliable.

Renewable or not?

Tap an energy resource, then tap the box it belongs in.

Human and physical geography meet

The two halves of geography constantly change each other. Human actions alter physical systems, and physical processes shape human life.

• Deforestation (human) reduces transpiration and increases run-off (physical) — raising flood risk.
• Burning fossil fuels (human) drives climate change (physical) — melting ice and raising sea levels.
• Building on flood plains (human) puts homes at risk when rivers flood (physical).
• A volcanic eruption (physical) can destroy farmland and force people to move (human).

Sustainability means meeting today's needs without wrecking the planet for future generations — using resources carefully, cutting waste and reducing emissions.

Match the key term to its meaning

Tap a term on the left, then its matching definition on the right.

Cause and effect

Measuring development

What happens on the hill after heavy rain?

The big ideas to know

You've covered the key ideas in the KS3 "Human and physical geography" topic. Press Finish to see your score.