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CHEMISTRY · Stage 9 · Chapter 13: Planet Earth and Continental Drift

Chemistry 13.4 Chapter 13 Review: Planet Earth and Continental Drift

5 min read 6 parts Lesson 4 of 5

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Lesson summary

13.4 Chapter 13 Review: Planet Earth and Continental Drift — Alhussan International Academy — Chemistry (Stages 7–9) notes: Revise the evidence for continental drift, plate boundaries and calculations of plate movement.Continental drift = the very slow movement of the continents …

  • Mesosaurus
  • Glossopteris
  • Other evidence
  • Moving apart
  • Finding speed
  • Ring of Fire

Part 1 of 6Continental drift and fossil evidence

  • Continental drift the very slow movement of the continents relative to each other over millions of years.
  • Mesosaurusfossils of this freshwater reptile appear in rocks in both South America and Africa, and it could not cross a salty ocean, so the continents must once have been joined.
  • Glossopterisfossils of this plant in several southern continents suggest they were part of Gondwana, the southern part of Pangaea.
  • Other evidencematching rock layers and the fit of coastlines add further support.

Part 2 of 6Tectonic plates and boundaries

  • Plates — the Earth's crust is divided into tectonic plates that rest on the mantle and move because of convection currents.
  • Collision — where two plates collide, the crust is squeezed and folded to form mountain chains.
    • A mountain chain on the boundary between the Arabian and Eurasian plates shows these plates are colliding and crumpling the crust.
  • Moving apart — magma rises and forms new crust, as at a mid-ocean ridge.
  • Sinking — where one plate sinks beneath another, trenches, volcanoes and earthquakes occur.
BoundaryMovementResult
ConstructiveMoving apartRidge, new crust
DestructiveCollidingMountains, trenches, volcanoes
ConservativeSliding pastEarthquakes

Part 3 of 6Calculations with plate speed

  • Formula — distance = speed × time.
  • Units — plates move a few centimetres per year, so convert centimetres to metres or kilometres at the end.
    • A plate moving at 2 cm per year travels 200 cm (2 m) in 100 years.
  • Finding speed — measure the distance moved on a map in km, convert to cm and divide by the number of years.

Part 4 of 6Earthquakes, volcanoes and plate maps

  • Plate boundariesmost earthquakes and volcanoes occur along them, so maps of their locations outline the plates.
  • Ring of Fireit follows the edges of the Pacific plate.
  • Stable regionsearthquakes are rare in the middle of continents.
  • Evidencesuch maps are further evidence that the crust is divided into moving plates.

Part 5 of 6Seafloor spreading evidence

  • New crust — it forms at mid-ocean ridges and moves outward.
  • Magnetic stripes — the symmetrical pattern of stripes on both sides of a ridge shows spreading.

Part 6 of 6Writing explanations

  • Structure — give the evidence, what it shows, and the conclusion.
    • The same fossils are found on both sides of the Atlantic, the animals could not have crossed the ocean, so the continents were once joined.
  • Using maps — refer to arrows, plate names and boundaries on the diagram.

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