The lithosphere is broken into giant plates that move a few centimetres a year. Their motion builds mountains, opens oceans and causes most earthquakes and volcanoes.
🌐 Evidence and mechanism
Alfred Wegener proposed continental drift in 1912. His evidence: the continents fit together like a jigsaw, matching fossils and rocks lie on separate continents, and ancient glacier marks appear in warm places. The missing piece was a mechanism: sea-floor spreading at mid-ocean ridges, and convection currents in the mantle that drag plates along.
Pangaea: single supercontinent about 250 million years ago
matching fossils: Mesosaurus in South America and Africa
mid-ocean ridge: new crust forms, older crust moves away
rock gets older with distance from the ridge
🖼️ See it
Divergent: mid-ocean ridges. Convergent: trenches and mountains. Transform: faults such as the San Andreas.
↔️ Three kinds of boundary
Divergent boundaries: plates move apart (mid-ocean ridges, rift valleys). Convergent: plates collide, forming mountains, trenches and volcanoes; an oceanic plate sinks (subduction) beneath a lighter plate. Transform: plates slide past each other (San Andreas Fault), causing earthquakes.
speed = distance / time
5 cm per year for 20 million years:
5 · 20 000 000 = 100 000 000 cm = 1000 km
1 km = 100 000 cm
Plates move about as fast as your fingernails grow, about 2 to 10 cm a year.
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Divergent
At a divergent boundary, plates:
Diverge means move apart.
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Transform
The San Andreas Fault is an example of a:
Sliding.
✏️ Quick check · 3 of 7
Wegener evidence
Which is evidence for continental drift?
Fossils.
✏️ Quick check · 4 of 7
Subduction
In subduction, the:
Sinking.
✍️ Type your answer · 5 of 7
A plate moves 5 cm per year. In 20 million years it moves 100 000 000 cm.
How many kilometres is that? (1 km = 100 000 cm)
Enter an exact answer, without rounding.
km
Divide by 100 000.
✍️ Type your answer · 6 of 7
A plate moves 2 cm a year.
How many cm does it move in 50 years?
Enter an exact answer, without rounding.
cm
Multiply.
✍️ Type your answer · 7 of 7
An ocean basin has widened by 5000 km over 200 million years.
What is the average widening, in km per million years?
Enter an exact answer, without rounding.
km
Divide.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
Sea-floor spreading occurs at:
Question 2 of 5
What drives plate motion?
Question 3 of 5
Mountain ranges like the Himalayas form at:
Question 4 of 5
Oceanic crust far from a ridge is:
Question 5 of 5
The supercontinent Wegener described was called:
Lesson 2 · Dynamic Earth
🌋 Earthquakes & Volcanoes
Earthquakes and volcanoes occur mostly along plate boundaries, a pattern called the Ring of Fire around the Pacific.
📳 Earthquakes
An earthquake is caused by sudden release of stored stress along a fault. The point underground is the focus; the point directly above on the surface is the epicentre. P-waves (primary) are faster and travel through solids and liquids; S-waves are slower and travel only through solids. The magnitude scale is logarithmic: each whole number is 10 times larger in wave amplitude.
P-wave speed 6 km/s, S-wave speed 3 km/s
distance = speed · time
P-wave in 50 s: 6 · 50 = 300 km
magnitude 7 vs 5: 10 · 10 = 100 times larger amplitude
🖼️ See it
Both are concentrated along plate boundaries, such as the Pacific “Ring of Fire”.
🌋 Volcanoes
Volcanoes form where magma reaches the surface: at subduction zones, at divergent boundaries and at hot spots (Hawaii). Shield volcanoes have gentle slopes from runny lava. Composite (stratovolcanoes) are steep and explosive. Hazards: lava, ash, gases and pyroclastic flows. Ash can also enrich soil.
lava flows 2 km/h → 3 hours: 2 · 3 = 6 km
S–P time lag with speeds 6 and 3 km/s over d km:
d/3 − d/6 = d/6
lag 100 s → d = 600 km
The S–P lag tells how far away an earthquake was. Three stations can locate the epicentre.
✏️ Quick check · 1 of 7
Epicentre
The epicentre of an earthquake is:
On the surface.
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S-waves
S-waves cannot travel through:
Not liquids.
✏️ Quick check · 3 of 7
Ring of Fire
The Ring of Fire is a zone of:
Pacific.
✏️ Quick check · 4 of 7
Shield volcano
A shield volcano has:
Wide and gentle.
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P-waves travel at 6 km/s.
How far do they travel in 50 s, in km?
Enter an exact answer, without rounding.
km
distance = speed · time.
✍️ Type your answer · 6 of 7
S-waves travel at 3 km/s.
How long, in seconds, to travel 600 km?
Enter an exact answer, without rounding.
s
time = distance ÷ speed.
✍️ Type your answer · 7 of 7
An earthquake of magnitude 7 is how many times larger in wave amplitude than one of magnitude 5?
Give the number.
Enter an exact answer, without rounding.
Each whole number is 10 times.
📝 Lesson quiz · 5 questions
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Question 1 of 5
Earthquakes occur when:
Question 2 of 5
Which wave arrives first at a seismograph?
Question 3 of 5
A tsunami is most often caused by:
Question 4 of 5
The instrument that records earthquakes is a:
Question 5 of 5
Hawaii’s volcanoes formed over a:
Lesson 3 · Weather
🌬️ Air Masses & Fronts
Air pressure differences create wind, and the meeting of different air masses creates fronts, where most stormy weather happens.
💨 Pressure, wind and altitude
Air flows from high pressure to low pressure: that is wind. High pressure usually brings clear weather; low pressure brings clouds and rain. Air thins with altitude, so pressure and temperature fall as you climb in the troposphere, about 6 °C for every 1000 m.
temperature falls about 6 °C per 1000 m
ground 20 °C, mountain top 3000 m up:
20 − 3 · 6 = 20 − 18 = 2 °C
air flows high → low pressure
🖼️ See it
Where two air masses meet, the lighter warm air is forced up, cools and forms clouds and rain.
⛈️ Fronts
An air mass is a large body of air with similar temperature and humidity. Where two meet, a front forms. At a cold front, cold air pushes under warm air, giving a narrow band of heavy rain and thunderstorms, then cooler weather. At a warm front, warm air rides over cold air, giving a wide area of light steady rain, then warmer weather.
cold front moves 30 km/h for 4 h: 30 · 4 = 120 km
cold front: heavy short rain, then cold, clear
warm front: long light rain, then warm, humid
Cold air is denser, so it wedges under warm air and forces it up quickly. That is why cold fronts are stormy.
✏️ Quick check · 1 of 7
Wind direction
Wind blows from:
High to low.
✏️ Quick check · 2 of 7
Cold front
A cold front often brings:
Short and stormy.
✏️ Quick check · 3 of 7
Warm front
Warm air at a warm front:
Rides over.
✏️ Quick check · 4 of 7
High pressure
High pressure usually brings:
Fair.
✍️ Type your answer · 5 of 7
Air temperature falls 6 °C per 1000 m. The ground is at 20 °C.
What is the temperature at 3000 m, in °C?
Enter an exact answer, without rounding.
°C
Subtract 3 · 6.
✍️ Type your answer · 6 of 7
A cold front moves at 30 km/h.
How far does it travel in 4 hours, in km?
Enter an exact answer, without rounding.
km
distance = speed · time.
✍️ Type your answer · 7 of 7
A front is 240 km away and moves at 40 km/h.
How many hours until it arrives?
Enter an exact answer, without rounding.
h
time = distance ÷ speed.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
An air mass is:
Question 2 of 5
Low pressure systems are usually associated with:
Question 3 of 5
After a cold front passes, the temperature usually:
Question 4 of 5
Which instrument shows that a storm may be coming?
Question 5 of 5
Winds are caused by:
Lesson 4 · Climate
🌴 Climate Zones & Biomes
Climate is the long-term pattern of weather. It depends mainly on latitude, altitude, ocean currents and distance from the sea.
🧭 Why climates differ
Near the equator, sunlight strikes directly and concentrates heat, so the tropics are warm. Near the poles, sunlight is spread over a larger area at a low angle, so it is cold. Altitude cools the air, and the sea moderates temperature, so coastal places have milder climates than inland ones. Ocean currents carry heat (the Gulf Stream warms northwest Europe).
Tropic of Cancer: 23.5° N, Tropic of Capricorn: 23.5° S
Arctic Circle = 90° − 23.5° = 66.5° N
tropics: between 23.5° S and 23.5° N = 47° wide
🖼️ See it
Temperature and rainfall decide which plants can grow, and the plants decide the animals that live there.
🌳 Biomes
A biome is a large region with a characteristic climate, plants and animals: tropical rainforest (hot, wet, very high biodiversity), desert (under 250 mm of rain a year), temperate forest, grassland, taiga (cold coniferous forest) and tundra (cold, treeless, frozen subsoil).
rainfall by month (mm): 20, 30, 10, 40 → total 100 mm
mean = 100/4 = 25 mm
desert: less than 250 mm per year
300 mm per year → not a desert
A climate graph shows temperature as a line and rainfall as bars for each month of the year.
✏️ Quick check · 1 of 7
Equator
Why is it hottest at the equator?
Angle of the Sun.
✏️ Quick check · 2 of 7
Altitude
Higher places are generally:
Thin air.
✏️ Quick check · 3 of 7
Tundra
Tundra is:
Cold and treeless.
✏️ Quick check · 4 of 7
Coastal climate
Compared with inland places, coastal places usually have:
The sea moderates.
✍️ Type your answer · 5 of 7
The Tropic of Cancer is at 23.5° N.
What latitude is the Arctic Circle? (90 − 23.5)
Enter an exact answer, without rounding.
°
Subtract.
✍️ Type your answer · 6 of 7
Monthly rainfall is 20, 30, 10 and 40 mm.
What is the mean, in mm?
Enter an exact answer, without rounding.
mm
Add and divide by 4.
✍️ Type your answer · 7 of 7
A desert gets less than 250 mm of rain a year. A place gets 20 mm a month.
What is its yearly total, in mm?
Enter an exact answer, without rounding.
mm
Multiply by 12.
📝 Lesson quiz · 5 questions
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Question 1 of 5
The Gulf Stream makes northwest Europe:
Question 2 of 5
Tropical rainforests have:
Question 3 of 5
A desert is defined by:
Question 4 of 5
Latitude is the distance:
Question 5 of 5
Climate is based on weather records over about:
Lesson 5 · Hydrosphere
🌊 Oceans
Oceans cover 71% of the planet. They store heat, move water in great currents and support most of Earth’s life.
🧂 The ocean floor and salt
The sea floor has continental shelves, steep slopes, flat abyssal plains, mid-ocean ridges and deep trenches (the Mariana Trench is about 11 000 m deep). Sea water is about 3.5% salt, that is 35 g in every 1000 g.
71% of the surface is ocean, so 100 − 71 = 29% is land
salinity 35 g per kg
2 kg of sea water: 2 · 35 = 70 g salt
sonar depth = (speed · time)/2
(1500 · 4)/2 = 3000 m
🖼️ See it
The Pacific alone is bigger than all of the Earth’s land put together.
🔁 Currents and tides
Surface currents are driven by winds and the Earth’s rotation, and circle the ocean basins. Deep currents are driven by differences in temperature and salinity (density). Tides are caused by the gravity of the Moon (and the Sun). Spring tides are the biggest and occur at new and full moon; neap tides are the smallest, at the quarter moons.
two high tides roughly every 24 h 50 min
tidal range = high − low
high 6 m, low 1 m: range = 5 m
spring tides: new moon and full moon
neap tides: first and last quarter
Water holds heat far better than air. Oceans soak up and spread most of the heat that reaches Earth.
✏️ Quick check · 1 of 7
Trench
The deepest parts of the ocean are the:
Plates sink here.
✏️ Quick check · 2 of 7
Tides
Tides are caused mainly by the:
Gravity.
✏️ Quick check · 3 of 7
Spring tides
Spring tides occur at:
Aligned.
✏️ Quick check · 4 of 7
Surface currents
Surface currents are mainly driven by:
Blowing.
✍️ Type your answer · 5 of 7
Oceans cover 71% of Earth’s surface.
What percentage is land?
Enter an exact answer, without rounding.
%
Subtract.
✍️ Type your answer · 6 of 7
Sea water has 35 g of salt per kg.
How many grams of salt in 2 kg?
Enter an exact answer, without rounding.
g
Multiply.
✍️ Type your answer · 7 of 7
A sonar pulse (1500 m/s) returns after 4 s.
What is the depth, in m? (Use (speed · time)/2)
Enter an exact answer, without rounding.
m
Halve it for the round trip.
📝 Lesson quiz · 5 questions
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Re-read the lesson, then give it another go.
Question 1 of 5
About how much of the Earth is covered by oceans?
Question 2 of 5
Sea water is salty mainly because of:
Question 3 of 5
Neap tides occur at:
Question 4 of 5
Deep ocean currents are driven by differences in:
Question 5 of 5
The continental shelf is:
Lesson 6 · Skills
🗺️ Maps & Coordinates
Maps let us locate places precisely and show the shape of the land. Coordinates, scales and contour lines are the language of maps.
📍 Latitude, longitude and time
Latitude lines run east–west, measured from the equator (0°) to the poles (90° N and S). Longitude lines run north–south, measured from the prime meridian (0°, through Greenwich) to 180° E and W. Earth turns 15° each hour, so every 15° of longitude is one hour of time difference.
360° / 24 h = 15° per hour
longitude 45° E: 45 / 15 = 3 hours ahead of Greenwich
noon in Greenwich → 3:00 pm there
longitude 75° W: 75/15 = 5 hours behind
🖼️ See it
Give latitude first, then longitude: for example 51° N, 0° names a place on the Prime Meridian.
⛰️ Scale and contour lines
A scale relates map distance to real distance (for example 1 cm = 5 km). Contour lines join points of equal elevation. Close lines mean a steep slope, wide spacing means a gentle slope, and circles of lines show a hill. The contour interval is the height difference between lines.
scale 1 cm : 5 km
map distance 7 cm → 7 · 5 = 35 km
contour interval 20 m
from 100 m line to 160 m line: 3 intervals = 60 m
Contour lines never cross, because one place cannot have two heights.
✏️ Quick check · 1 of 7
Latitude
Lines of latitude run:
Parallel to the equator.
✏️ Quick check · 2 of 7
Prime meridian
The prime meridian is at:
Zero longitude.
✏️ Quick check · 3 of 7
Steep slope
Closely spaced contour lines show:
Close = steep.
✏️ Quick check · 4 of 7
Equator
The equator is at:
Zero latitude.
✍️ Type your answer · 5 of 7
Earth turns 360° in 24 hours.
How many degrees of longitude is one hour?
Enter an exact answer, without rounding.
°
Divide.
✍️ Type your answer · 6 of 7
A city is at longitude 45° E. How many hours ahead of Greenwich is its time?
Give the number.
Enter an exact answer, without rounding.
h
Divide by 15.
✍️ Type your answer · 7 of 7
On a map, 1 cm = 5 km. Two towns are 7 cm apart.
What is the real distance, in km?
Enter an exact answer, without rounding.
km
Multiply.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
Longitude is measured from the:
Question 2 of 5
A contour interval is the:
Question 3 of 5
Which pair gives a place’s exact position?
Question 4 of 5
Contour lines that form closed circles show a:
Question 5 of 5
The map key (legend) explains the:
Final Challenge
🏆 12-Question Challenge Quiz
Questions from every topic in this course. Pick an answer for each one, then hit Check My Answers.
0 / 12
💪 Keep practicing — go back through the lessons and retake the quiz!
Q1 · Plate Tectonics
A deep ocean trench is most likely found at a:
Q2 · Plate Tectonics
The supercontinent Wegener described was called:
Q3 · Earthquakes & Volcanoes
The focus of an earthquake is the:
Q4 · Earthquakes & Volcanoes
Hawaii’s volcanoes formed over a:
Q5 · Air Masses & Fronts
A narrow band of heavy rain and thunderstorms is typical of a: