Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

13.1Chapter 13: Planet Earth and Continental Drift

Continental drift — Alhussan Chemistry - Stage 9 Revision Notes & Topical Questions

5 min read 9 parts Lesson 1 of 5 1 quiz

📚 Alhussan Chemistry - Stage 9 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

13.1 Continental drift — Wegener's Pangaea Hypothesis — Alhussan International Academy — Chemistry (Stages 7–9) notes: Define continental drift, explain how tectonic plates move, and describe Wegener's hypothesis and why it was at first doubted.Plates — the surface of the Earth c…

  • Boundaries
  • Plate names
  • Convection currents
  • Fit of the continents
  • Rocks and mountains
  • Climate evidence

Part 1 of 7Tectonic plates

Plates
  • Plates the surface of the Earth consists of about 12 tectonic plates.
  • Each is a slab of solid rock made up of a piece of the Earth's crust and the top part of the mantle below it.
Boundaries
  • Boundaries plates meet at plate boundaries, where earthquakes and volcanoes are mostly found, which is evidence for tectonic plates.
Example
  • Example in Iceland a gap separates the North American plate and the Eurasian plate and gets wider every year.
Plate names
  • North American, Eurasian, African, South American, Pacific, Australian, Antarctic, Juan de Fuca, Caribbean and Filipino.

Part 2 of 7Why plates move

Density
  • Density tectonic plate rock is less dense than the mantle below it, so the plates rest on the mantle.
Heat
  • Heat natural processes deep inside the Earth heat the mantle.
Convection currents
  • Convection currents the heat drives convection currents in the mantle, which make the tectonic plates move.
Speed
  • Speed plates move slowly, at a few centimetres a year, about the speed at which fingernails grow.

Part 3 of 7Continental drift

Continental drift
Continental drift the movement of tectonic plates, and the continents on them, over millions of years.
  • Over millions of years the plates have moved many kilometres.
Maps
  • Maps maps for the Permian period, the Jurassic period (150 million years ago) and today show how the continents have moved.
    • (225 million years ago)

Part 4 of 7Wegener's hypothesis

Pangaea
  • Pangaea in 1912 the German scientist Alfred Wegener proposed that all the continents were once joined in one supercontinent called Pangaea,
  • meaning "all earth", about 250 million years ago.
Break-up
  • Break-up over millions of years Pangaea broke up and the pieces slowly moved apart to their present positions.
Today
  • Today the continents are still moving at a few centimetres a year.

Part 5 of 7Wegener's evidence

Fit of the continents
  • Fit of the continents the east coast of South America fits the west coast of Africa.
Fossils
  • Fossils identical fossils of land animals and plants, such as Mesosaurus and Glossopteris, are found on continents now separated by oceans.
Rocks and mountains
  • Rocks and mountains matching rock types and mountain ranges continue across oceans.
Climate evidence
  • Climate evidence glacial deposits in warm regions such as India and Africa,
    • and coal formed from tropical plants in Antarctica, suggest these lands were once in different climates.
Independent lines
  • Independent lines combining several independent lines of evidence makes a scientific case convincing.
  • Matching fossils could be explained by land bridges, but matching mountain belts and glacial deposits are harder to explain that way.

Part 6 of 7Why people doubted Wegener

No mechanism
  • Wegener could not explain how continents could plough through solid ocean floor.
  • His suggestion of tidal forces or the spin of the Earth was shown to be far too weak.
Other geologists
  • Other geologists many, especially those who believed in a fixed Earth with sinking land bridges, rejected the idea.
Background
  • Wegener was a meteorologist and polar explorer rather than a geologist.
  • He published his ideas in the book The Origin of Continents and Oceans.
Death
  • Death he died in 1930 on an expedition to Greenland, before his idea was accepted.

Part 7 of 7Later acceptance

1New evidence
  • New evidence in the 1950s and 1960s, seafloor spreading, magnetic stripes and earthquake patterns provided a mechanism, convection currents in the mantle.
2Technology
  • Technology sonar and magnetometers mapped the ocean floor, about forty years after his death.
3Plate tectonics
  • Wegener's ideas became part of the theory of plate tectonics.
4How science develops
  • How science develops a hypothesis is proposed, tested and challenged, and is accepted when supported by new evidence and a convincing explanation.

Key terms

TermMeaning
Pangaeathe supercontinent that existed about 250 million years ago.
Hypothesisa testable explanation based on evidence.
Continental driftthe slow movement of the continents over geological time.
Plate tectonicsthe theory that the crust is split into moving plates.
Convection currenta circulating flow in a fluid caused by heating.
Tectonic platea slab of the Earth's crust and upper mantle.

Avoid these mistakes

1
Thinking the continents moved quickly — they move a few centimetres a year.
2
Saying Pangaea broke up 25 million years ago — it began breaking up over 200 million years ago.
3
Assuming Wegener had a complete explanation — he lacked a mechanism.
4
Saying Wegener discovered plate tectonics — he proposed continental drift, and plate tectonics came later.

Last updated: