Evidence for Continental Drift: Jigsaw Fit, Matching Rock Ages, Tillite, Placer Deposits, Fossil Distribution
Geography › Plate Tectonics and Distribution of Continents and Oceans · Topic 4.2
Wegener and later scientists collected evidence to show that the continents were once joined. The coastlines of South America and Africa fit like a jigsaw, especially along the edge of the continental shelf. Rocks of the same age and type occur on both sides of the Atlantic. Glacial tillite of the same age is found in India, Africa, South America, Australia and Antarctica. Fossils of the same plants and animals, such as Glossopteris and Mesosaurus, are found on widely separated continents, and gold placers in Ghana match their source in Brazil.
5 min read · UPSC Prelims · Geography · Plate Tectonics and Distribution of Continents and Oceans
At a Glance
- Coastline fit Best at the 1,000-fathom line
- Rocks Same ages across the Atlantic
- Tillite Glacial rocks in all southern continents
- Placer deposits Ghana gold matched with Brazil
- Fossils Glossopteris, Mesosaurus, Lystrosaurus
- Exam link UPSC Prelims, Geography: Plate Tectonics and Distribution of Continents and Oceans
Where Does It Fit?
This topic follows the statement of the theory and gives the proofs offered for it. These proofs convinced some scientists, but they did not show how continents could move, which is the subject of the next topic. Previous topic: Continental Drift Theory (Alfred Wegener, 1912): Pangea, Panthalassa, Laurasia, Gondwanaland. Next topic: Forces of Drifting: Pole-Fleeing Force, Tidal Force.
What Evidence Did Wegener Give?
| Evidence | Observation |
|---|---|
| Jigsaw fit | The coasts of South America and Africa fit closely, especially along the edge of the continental shelf |
| Rocks of the same age | Rock belts of 2,000 million years in Brazil match those of West Africa; the Appalachian mountains match the Caledonian mountains of Scotland and Scandinavia |
| Fossils | The same land fossils on widely separated continents, such as Mesosaurus, a freshwater reptile, in South America and southern Africa, and the seed fern Glossopteris across the southern continents including India |
| Glaciation | Tillite deposits of the same age in India, South Africa, Australia, South America and Antarctica show a common ice age |
| Placer deposits | Gold-bearing rocks of Ghana match the source of gold placers in Brazil |
| Climate | Coal in Antarctica shows that warm, wet forests once grew near the pole |
The evidence from the Gondwana rocks of India, which hold coal and the fossils of Glossopteris, is a key proof that the Indian peninsula was part of Gondwanaland, a theme developed in Plate Tectonics: Major and Minor Lithospheric Plates.
How Well Do the Coastlines Fit?
The first clue, noticed by mapmakers centuries ago, is that the east coast of South America and the west coast of Africa look like pieces of a jigsaw. A rough fit along the present coastline is poor, because waves and rivers have changed the shore. The fit is better along the edge of the continental shelf, at a depth of about 1,000 fathoms (nearly 2,000 metres). In 1965 the British scientists Edward Bullard, J. E. Everett and A. G. Smith used a computer to fit the continents along this line, and found a close match with very little overlap or gap. The same method also fits India, Australia and Antarctica against the south of Africa.
What Do Rocks, Fossils and Deposits Show?
| Evidence | What it shows |
|---|---|
| Matching rock ages and structures | A belt of rocks about 2,000 million years old in Brazil matches rocks of the same age in West Africa. The mountain belts of the Appalachians in North America and the Caledonides of Scotland and Norway line up when the Atlantic is closed |
| Tillite | Tillite is the rock formed from glacial till. Layers of the same age, about 300 million years, are found in India, Africa, South America, Australia and Antarctica, which suggests that these lands lay together near the South Pole under one ice sheet. They are part of the Gondwana system of rocks |
| Placer deposits | Gold-bearing placer deposits are found on the coast of Ghana, but the source rocks do not exist there. The matching gold-bearing rocks occur in Brazil, from where the deposits were washed when the two lay together |
| Fossil distribution | Mesosaurus, a small freshwater reptile, is found in South Africa and Brazil only. The seed fern Glossopteris is found in India, Australia, South Africa, South America and Antarctica. Lystrosaurus has been found in Antarctica, India and South Africa |
| Ancient climates | Coal beds in cold Antarctica show it was once warm and near the equator; glacial deposits in tropical India show it was once near the pole |
These plants and animals could not cross wide oceans. Wegener argued that this makes sense only if the continents were joined at the time.
How Is Gondwana Linked to India?
India holds a rich record of the Gondwana system. The Gondwana beds of the Damodar, Mahanadi, Godavari and Narmada valleys contain coal formed from Glossopteris forests about 300 to 250 million years ago, resting on glacial tillite at the base. These coal measures supply most of India’s coal, and are described in Geological History of the Earth. The same sequence of tillite, then coal, then sandstone occurs in the other southern continents, which was a strong confirmation of the theory.
As an analytical point, none of these facts alone proves drift, but together they are consistent, and the later evidence of sea-floor spreading, magnetic stripes and plate motions measured by satellites has turned the theory into a firm part of science. The forces proposed to explain it are in Forces of Drifting: Pole-Fleeing Force, Tidal Force.
Why Is This Topic Important?
- Foundation Precursor to plate tectonics
- Evidences Frequent Prelims theme
- India Gondwana link
What Came Next?
The next topic describes the forces that Wegener proposed to drive the drifting of continents. Next topic: Forces of Drifting: Pole-Fleeing Force, Tidal Force.
Key People and Terms
- Pangaea Single supercontinent
- Panthalassa Ocean around Pangaea
- Laurasia Northern landmass
- Gondwanaland Southern landmass
- Tillite Rock formed from glacial deposits
- Glossopteris Fossil seed fern of Gondwana
Exam Corner
Points to Remember
- Proposed by Alfred Wegener in 1912.
- Pangaea began to split about 200 million years ago.
- Laurasia in the north, Gondwanaland in the south.
- Forces: pole-fleeing and tidal.
- Evidence included Glossopteris and tillite.
Do Not Confuse With
- Pangaea and Panthalassa Land versus ocean
- Laurasia and Gondwanaland North versus south
- Continental drift and plate tectonics Continents moving alone versus carried on plates
Memory Hook
One land, one sea; two pieces, many parts; fit, fossils, ice and rock, but no force to push.
Mains Angle
Questions ask for evidence and limitations. These points add depth.
- Evidence Fit, fossils, glaciation
- Limitation No adequate mechanism
- Legacy Led to seafloor spreading
A Question You May Face
An original practice question, not a past paper question.
“Critically examine Wegener’s theory of continental drift and the evidence for it.”
How to Answer
- Theory Pangaea and its breakup.
- Evidence Fit, fossils, rocks.
- Criticism Forces too weak.
- Legacy Plate tectonics.
GS Relevance
Frequently Asked Questions
What is the evidence for continental drift?
The evidence includes the jigsaw fit of the coasts of South America and Africa, matching rock belts across the Atlantic, the same fossils such as Mesosaurus and Glossopteris on separated continents, tillite deposits of a common ice age, and coal in Antarctica.
What is tillite and why is it evidence for drift?
Tillite is a sedimentary rock formed from the hardened till deposited by glaciers. Tillite beds of the same age, about 300 million years old, are found in India, Africa, South America, Australia and Antarctica, which suggests that these lands lay together under a single ice sheet near the South Pole.
Which fossils support continental drift?
Fossils of Glossopteris, a seed fern, occur in India, Australia, South Africa, South America and Antarctica. Mesosaurus, a freshwater reptile, is found only in South Africa and Brazil. Such land and freshwater species could not have crossed wide oceans, so the lands must have been joined.
How well do the coastlines of South America and Africa fit?
A rough fit along the present coastline is poor, but along the edge of the continental shelf, about 1,000 fathoms deep, the fit is very close. In 1965 Bullard, Everett and Smith used a computer to fit the two continents and found only small gaps and overlaps.
What is the placer deposit evidence?
Gold-bearing placer deposits are found on the coast of Ghana in West Africa, but the rocks that were the source of the gold do not occur there. The matching gold-bearing rocks lie in Brazil, so the deposits were probably washed from Brazil when the two continents were joined.
PYQ Practice — Statement Analysis
1 Glossopteris fossils support the idea of continental drift.
They occur on separated southern continents.
2 Glossopteris fossils are found in India and Antarctica.
This points to a joined Gondwanaland.
3 Mesosaurus fossils are found in the oceans only.
It was a freshwater reptile of South Africa and Brazil.
4 Tillite deposits of the same age occur in several southern continents.
This is evidence of a common ice sheet.
Past Mains Questions on This Topic
This topic comes under Plate Tectonics and Distribution of Continents and Oceans. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
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