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10.3Earth and Space 01. The Earth

Explain why the jigsaw appearance of continental coasts, location… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 9 parts Lesson 3 of 3 1 quiz

📚 Cambridge Checkpoint Science 0893 Hub / Topical Revision
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10.3 Evidence for tectonic plates — CHECKPOINT - Lower Secondary Science 0893 notes: Explain why the jigsaw fit of the coasts, the location of volcanoes and earthquakes, the fossil record and magnetic alignment in crustal rocks are evidence for tectonic plates.Continental drift —…

  • Coastlines
  • Matching fossils
  • Rock layers
  • Magnetic rocks
  • Magnetic reversals
  • Mid-ocean ridge

Section 1 of 9Wegener's continental drift

Continental drift
  • Continental drift the idea, proposed by Alfred Wegener in 1912, that the continents were once one large landmass that broke up and drifted apart.
  • The supercontinent was called Pangaea.
Rejection
  • Rejection many scientists did not accept the idea because Wegener could not explain how continents could move.
  • Plate tectonics later provided the explanation.

Section 2 of 9Jigsaw fit of the coasts

  • Coastlines
    • the coasts of South America and Africa fit together like jigsaw pieces.
    • This suggests the continents were once joined and then drifted apart.

Section 3 of 9Fossil record

  • Matching fossils
    • the same fossils of land animals and plants are found on continents now separated by oceans.
    • These organisms could not have crossed an ocean, so the continents must once have been joined.

Section 4 of 9Matching rocks

  • Rock layers
    • rock types and rock layers match up on different continents where the coasts fit together.
    • Mountain chains line up across the oceans when the continents are placed together.

Section 5 of 9Volcanoes and earthquakes

  • Location
    • earthquakes and volcanoes occur in narrow belts that mark the edges of the tectonic plates.
    • The Pacific Ring of Fire follows plate boundaries and shows that plates are moving.

Section 6 of 9Magnetic alignment in the crust

Magnetic rocks
  • Magnetic rocks iron-rich minerals in rocks line up with the Earth's magnetic field when the rock forms.
  • Rocks either side of a mid-ocean ridge show matching magnetic stripes, so new crust is forming and spreading outwards.
Magnetic reversals
  • Magnetic reversals the Earth's magnetic field has reversed many times, and these reversals are recorded in the rock.
  • Older rock lies further from the ridge, which shows the sea floor is spreading.

Section 7 of 9Why the plates move

  • Cause
    • heat from the core drives convection currents in the mantle, and these currents move the plates by about 4 cm a year.
    • Slow movement over millions of years explains the large changes in the positions of the continents.

Section 8 of 9Key terms

TermMeaning
Continental driftThe slow movement of the continents over millions of years.
PangaeaThe supercontinent that existed about 225 million years ago.
FossilThe preserved remains or traces of a once-living organism in rock.
Mid-ocean ridgeA boundary on the sea floor where plates move apart and new crust forms.
Convection currentCirculating movement in the mantle caused by heating.
EvidenceFacts from observations that support an idea.

Section 9 of 9Exam technique

1
Believing the continents have never moved — the evidence shows they have drifted over millions of years.
2
Saying fossils prove animals swam between continents — the same fossils show the land was once joined.
3
Thinking Wegener explained the cause of drift — he could not, which is why his idea was rejected at first.
4
Thinking plates are only under the continents — oceanic plates carry the ocean floors.

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