Continental Drift
Look at a world map. Look at the bulge of Brazil and the dent in Africa. Now ask the question a schoolboy asked in 1910, and that a whole century of scientists spent arguing about.
What if they used to fit together? They did. The ground you are standing on has travelled thousands of kilometres to get here, it has not stopped, and it is the reason this country shakes.
You will rebuild Pangaea
Drag seven continents back into one supercontinent with your own hands. Africa stays put; everything else has to come home.
You will line up the evidence
Fossils, mountain belts, ancient ice and coal — switch them on and watch four broken lines become four whole ones.
You will find your own islands
The Philippines sits in a vice, with sea floor diving under it from both sides. Section 09 is a map of exactly why.
How to use this
Work through it in order — each section answers the question the last one leaves hanging. Your place is saved automatically, so you can close the page and come back. Arrow keys move between sections, and the 🖨 button prints the whole thing as a reviewer.
One man, one map, one very unpopular idea
In 1912 a German weather scientist named Alfred Wegener stood up in front of a room of geologists and told them the continents move. They laughed at him. He was right.
Wegener was not the first person to notice that South America and Africa look like two halves of something torn apart. Map-makers had been remarking on it since the 1500s. What Wegener did was take the observation seriously enough to build a theory on it — and then spend twenty years collecting evidence from four continents to support it.
His claim was this: about 250 million years ago every piece of land on Earth was joined into a single supercontinent. He called it Pangaea, from the Greek for all the Earth. Around it was one enormous ocean, Panthalassa. Then Pangaea broke apart, and the pieces have been drifting ever since.
🧩 Put Pangaea back together
0 of 8 in placeDrag a continent to move it. Select one and use the turn buttons to rotate it. Africa is bolted down — real reconstructions hold one continent still and describe everything else relative to it, because "moved" only means anything compared to something.
That is Pangaea
One landmass, one ocean. Notice that it is not centred on the equator: most of it sat in the southern half of the world, and the far south of it was frozen. Remember that — it becomes evidence in the next section.
Laurasia and Gondwana
Pangaea did not shatter all at once. It first split into two: Laurasia in the north — North America, Europe, most of Asia — and Gondwana in the south: South America, Africa, India, Australia and Antarctica. Almost every fossil argument in this lesson is a Gondwana argument.
Flat maps stretch the poles
Antarctica is drawn here as a compact blob, not the wide white smear you see on a classroom wall map. Both are wrong in different ways: a flat map cannot show a round Earth honestly, and near the poles it stretches everything sideways. This version keeps Antarctica the right size, which is what a reconstruction needs.
He did not live to see it
Wegener died in 1930 on the Greenland ice sheet, on an expedition to resupply a weather station. He was fifty. His theory was still being taught as a curiosity — something a meteorologist had got wrong — for another thirty years.
Four clues that only make sense one way
Any one of these could be argued away. All four together, pointing at the same answer, are very hard to explain any other way — and that is what evidence means.
🗺️ The evidence map
Switch a clue on. Then switch between today and Pangaea and watch what happens to it. Nothing about the coloured bands is recalculated when you do that — they are fixed to the continents, and they line up only because the continents do.
The fit
The east coast of South America and the west coast of Africa are close to being the same line. Coastlines shift with sea level, so the fit is not perfect — but match them at the edge of the continental shelf, the true rim of the continent under shallow water, and the gap almost disappears.
A jigsaw fit on its own proves nothing. Two torn pieces of paper fit; so do two random coastlines if you squint. It is the next three clues that make it an argument.
The fossils
Four species, on continents now separated by whole oceans, and not one of them could have made the crossing.
- Mesosaurus — a freshwater reptile. Brazil and South Africa only.
- Cynognathus — a land reptile the size of a big dog.
- Lystrosaurus — Africa, India and Antarctica.
- Glossopteris — a fern whose seeds are far too heavy to float or blow across an ocean.
The rocks and mountains
The Appalachian Mountains of eastern North America stop dead at the coast. The same rock, of the same age, folded in the same event, starts again in Scotland, Ireland and Scandinavia. The Cape Fold Belt of South Africa matches the Sierra de la Ventana in Argentina the same way. Mountain ranges do not stop at coastlines for any good reason — unless the coastline is a cut.
The ancient climate
About 300 million years ago an ice sheet scratched deep grooves into solid rock and dumped rubble across India, Australia, southern Africa and South America — places that are now tropical. In the same period, tropical swamps were laying down coal in what is now Antarctica. Either the climate went insane in five places at once, or those five places used to be somewhere else.
The scratches point the same way
The best detail in the whole case: the grooves gouged by that ice sheet run in a consistent direction across four continents. Put the continents back together and the grooves all radiate outward from one centre, the way scratches spread from the middle of a single ice cap. Leave the continents where they are and the ice has to have flowed uphill out of the sea.
So why did nobody believe him?
Because good evidence is not enough. Wegener could say what had happened but not how, and a theory without a mechanism is a very good story.
Wegener's own suggestion was that the continents ploughed through the ocean floor, driven by the Earth's spin and the pull of the tides. Physicists checked the numbers and demolished it: those forces are far too weak, ocean floor is far too strong, and a continent trying to plough through it would break apart long before it moved anywhere. They were right, and Wegener never found a better answer.
What follows is the part of science that textbooks usually skip. Below are seven real objections. For each one, pick the later discovery that finally answered it — and notice how many of them came from the bottom of the sea, which is the one place nobody in 1920 could look.
⚖️ Objection and answer
Exam trap
If you are asked why continental drift was rejected, the answer is not "because the evidence was weak" and not "because Wegener was a meteorologist, not a geologist". Both are things people said at the time, and neither is the real reason. The real reason is that he could not explain what force moved the continents.
The answer was under the ocean the whole time
The Second World War put sonar on every warship. When the surveys were finally added up, the sea floor turned out to be nothing like the flat, ancient mud everybody had assumed.
Running down the middle of the Atlantic is a mountain range 16,000 km long with a valley along its crest. Around the edge of the Pacific are trenches deeper than Everest is tall. And when ships started dating the rock, the pattern was unmistakable: the floor is youngest at the ridges and gets steadily older the further you go from them — and nowhere on Earth is it older than about 200 million years.
In 1962 Harry Hess put it together. New sea floor is made at the ridge, spreads outward on both sides, and eventually sinks back into the mantle at a trench. Sea-floor spreading. The continents never had to plough through anything. They are passengers.
🧲 The ridge, and the bar code it prints
The Earth's magnetic field flips over every so often, and cooling lava freezes in whichever direction was current at the time. So the sea floor keeps a dated record. Set a spreading rate and a length of time, then tap anywhere on the crust.
Two identical bar codes
The stripes are not evenly spaced — some magnetic periods lasted a million years, some lasted a hundred thousand. That irregular pattern is a fingerprint, and it appears in the same order, at the same widths, on both sides of the ridge. There is only one way to print two matching bar codes: print them in the same place and then move them apart. Vine and Matthews published this in 1963, and the argument was effectively over.
Where the old floor goes
If crust were only ever made, the planet would be inflating. It is not: the old floor sinks back down at trenches, a process called subduction. That is why sea floor never gets to be older than about 200 million years, while continental rock survives for billions — the continents are too light to sink, so they simply ride around on top and never get recycled.
From drift to plate tectonics
Add sea-floor spreading to Wegener's evidence and you get plate tectonics: the Earth's rigid outer shell is broken into a few large plates, and those plates move. It is not a rival to continental drift — it keeps every fossil and every glacier scratch Wegener ever collected, and finally supplies the engine he was missing.
The plates, and the three things that happen at their edges
A plate is not a continent. A plate is the lithosphere — the crust plus the rigid top of the mantle, about 100 km thick — and most plates carry both continent and ocean floor at once.
Lithosphere on asthenosphere
Under the rigid lithosphere is the asthenosphere: mantle rock that is hot enough to flow, very slowly, without melting. It is solid — you could stand on it if you could survive the temperature — but over millions of years it behaves like extremely stiff toffee. The plates slide on it.
The middles are boring
Almost every earthquake, volcano, trench and young mountain range on Earth sits on a plate boundary. The middle of a plate is one of the quietest places you can be. Look at where the coloured lines on the map below are, then think about which countries make the news for earthquakes.
🌐 The world's plate boundaries
Tap a line on the map, or a name in the list, to see what is happening along it.
✂️ What a boundary looks like in cross-section
Seen from the sideSix settings — the three kinds of boundary, and the different results you get depending on which sort of crust is on each side.
The three-second test
Faced with any boundary in an exam, ask one question: is crust being made, destroyed, or neither? Made → divergent. Destroyed → convergent. Neither → transform. Everything else — the trench, the volcanoes, the mountain range, the island arc — follows from that answer.
What actually moves a plate
This is the question Wegener could not answer. It took until the 1970s to answer it properly, and the answer turned out to be mostly gravity.
For a long time the textbook picture was a plate sitting on a conveyor belt of convecting mantle, dragged along from below. That picture is not wrong, but it is not the main event either. The two forces that do most of the work both come from the plate's own weight.
⚙️ Switch the forces off and see what happens
Turn each force on or off. Watch the speed. Then decide for yourself which one you would name first in an exam answer.
The chain on the table
The best mental picture for slab pull: a chain lying on a table with one end hanging over the edge. Nothing pushes the chain. The hanging part is heavy, and it drags the rest along — faster and faster as more of it goes over. A subducting plate is doing exactly that, except that the "table" is the whole Pacific and the chain has been sliding for a hundred million years.
A planet still cooling down
Two sources: leftover heat from the Earth's formation 4.5 billion years ago, and radioactive elements in the mantle decaying and releasing heat as they go. That heat drives the convection, the convection keeps the mantle soft, and everything else in this lesson follows. When the Earth finally cools, plate tectonics will stop — as it appears to have done on Mars.
Fast plates have sinking edges
You can test slab pull without any equipment. List the plates by speed. The fast ones — Pacific, Nazca, Cocos, Philippine Sea — all have long subducting edges. The slow ones — African, Eurasian, Antarctic — have almost none. If convection from below were the main driver, plate speed would have nothing to do with what is happening at the edges. It has everything to do with it.
How fast, and how far
Plates move at between about 2 and 10 centimetres a year — roughly the rate your fingernails grow. Given a hundred million years, that builds an ocean.
Here is the conversion worth memorising, because it collapses two nasty ones into a single number: 1 cm/year for 1 million years = 1,000,000 cm = 10 km. So if you are working in centimetres per year and millions of years, the distance in kilometres is just rate × time × 10. Nothing else to convert.
🧮 Seven problems, two modes
"Show the working" prints every step. "Check my answer" hides all of it, marks what you type, and tells you which slip you made — which is the mode that actually prepares you for an exam.
The mistake almost everybody makes
Not the arithmetic — the units. A centimetre that never became a kilometre, or a "50 million years" that got used as "50 years". Both produce an answer with exactly the right digits and a wildly wrong size. If your answer looks right but is out by a factor of 100,000 or a million, you have not made a maths error; you have skipped a conversion. Do the conversion once, at the start.
Three hundred million years, on one slider
Everything you have learned so far, running as a film. Drag it, or press play and watch the world you know assemble itself out of Pangaea.
⏳ The drift, start to finish
Permian
India is the sprinter
Every other continent ambles. India tears away from Africa about 130 million years ago and crosses roughly 6,000 km of open ocean in 80 million years — around 12 centimetres a year, faster than any continent before or since. Then it hits Asia, stops dead, and the Himalayas start going up. They are still going up.
The last stop is a guess
Push the slider past today and the continents keep going in the directions they are currently measured to be going. That is an extrapolation, not an observation — the map is marked as such. It is a reasonable guess for 50 million years and pure speculation beyond it, because new boundaries can form and old ones can die.
Why this country shakes
Most countries sit near one plate boundary, or none. The Philippines sits in the middle of several at once, with sea floor diving underneath it from both directions.
Our islands are part of the Philippine Mobile Belt: a crushed, broken zone caught between the Philippine Sea Plate pushing in from the east at about 8 cm a year and the Eurasian Plate on the west. Neither side is giving way. The belt in between is being squeezed, sheared and shoved sideways — and that single sentence explains the trenches, the volcanoes, the faults and the earthquakes.
📍 Your own plate map
The little triangles on a trench point towards the plate that is staying on top. Look at which way they point on each side of the country.
Two volcano chains, two slabs
Pinatubo and Taal are fed by the Manila Trench on the west. Mayon and the Bicol volcanoes are fed by the Philippine Trench on the east. Same process, opposite directions.
Tsunami risk is eastern
Big offshore thrust earthquakes lift the sea floor and the water above it. The Pacific seaboard and the Moro Gulf are the historical danger zones.
The Ring of Fire
The horseshoe of trenches around the Pacific, where roughly 90% of the world's earthquakes happen. We are on it. So are Japan, Indonesia, Chile and California.
The islands are made of this
The Philippines is not a piece of continent that broke off something. Large parts of it were built at convergent boundaries — volcanic island arcs, one eruption at a time, then jammed together by the squeeze. The country is a collection of pieces that arrived separately and were welded into an archipelago. That is why the geology changes so much between one island and the next.
Why this is not only an exam topic
The 2013 Bohol earthquake happened on a fault that was not on any map. There is no way to predict the day an earthquake will strike, and there probably never will be. What plate tectonics does give us is the where and the how often — which is enough to decide how a building should be designed, where a school should be built, and what to do in the first ten seconds.
Sort it: which kind of boundary?
Twelve statements, three bins. Drag one in, or tap the token and then tap a bin. Every correct drop tells you why.
Ask about the crust
New crust being made means the plates are moving apart. Crust being destroyed, or piled into mountains, means they are moving together. If neither is happening but the ground still shakes, they are sliding past. There is no fourth option.
Volcanoes narrow it down fast
Volcanoes at a boundary mean divergent or convergent — you need either rising mantle or a sinking slab to make magma. A boundary with big earthquakes and no volcanoes at all is almost certainly transform. Continent-meets-continent is the one exception worth remembering: huge mountains, huge earthquakes, no volcanoes.
Flashcard review
The words you need before the quiz. Tap a card to flip it. Cover the answer and say the definition out loud first — that is what makes it stick.
Practice quiz
Sixteen questions. You get an explanation after every answer — read it even when you get it right.
The questions shuffle
Every attempt reorders the items, so you cannot memorise the sequence — only the geography.
Say the reason out loud
Before you tap, finish this sentence: "because ___". If you cannot, you are guessing, and the explanation afterwards is the part you need.
Your best score is kept
Retake it as often as you like. The score is saved on this device only — nothing leaves your browser.
Summary & cheat sheet
Everything in the lesson, on one page. Print this one — the 🖨 button at the top right saves it as a PDF.
| Topic | The rule | Remember |
|---|
If you remember nothing else
- The continents were once joined in Pangaea, and they have moved apart.
- Four kinds of evidence say so: the fit, the fossils, the rocks, the climate.
- Nobody believed it for fifty years because there was no mechanism.
- The mechanism is sea-floor spreading — crust made at ridges, destroyed at trenches.
- Plate tectonics is that mechanism plus Wegener's evidence, and it is still running today.
Three sentences that lose marks
"The continents float on molten rock." They do not — the asthenosphere is
solid, just soft.
"Plate tectonics disproved continental drift." It did the opposite; it
explained it.
"A plate is a continent." A plate is lithosphere, and most plates carry
ocean floor as well as land.
Before you close this
On exam day, write these three lines at the top of your paper before you read a single question: fit · fossils · rocks · climate · divergent makes, convergent destroys, transform neither · 1 cm/year for 1 million years = 10 km. Then, for any question about a place, find the boundary first and describe the place second.