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13.2Chapter 13: Planet Earth and Continental Drift

Evidence from fossils — Alhussan Chemistry - Stage 9 Revision Notes & Topical Questions

5 min read 8 parts Lesson 2 of 5 1 quiz

📚 Alhussan Chemistry - Stage 9 Hub / Topical Revision
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13.2 Evidence from fossils — Mesosaurus, Glossopteris and Rock Strata — Alhussan International Academy — Chemistry (Stages 7–9) notes: Use fossil and rock evidence to support the idea that continents were once joined and that Antarctica once had a warmer climate.Fossils = the pre…

  • Importance
  • Scott's expedition
  • The fossils
  • Same species elsewhere
  • Lystrosaurus
  • Cynognathus

Section 1 of 8What fossils are

Fossils
Fossils the preserved remains or traces of organisms that lived long ago, usually found in sedimentary rock.
Importance
  • Importance they show what lived where and when.
  • If the same kind of fossil is found on continents now separated by thousands of kilometres of ocean, scientists must explain how it got there.
Wegener
  • Alfred Wegener used fossil evidence in 1912 to support his hypothesis that the continents were once a single piece of land that broke up and drifted apart.

Section 2 of 8Evidence from trees: Glossopteris and Antarctica

Scott's expedition
  • Scott's expedition in 1912 Robert Falcon Scott's team, returning from the South Pole, collected heavy fossils from a rocky area and kept them.
  • A rescue team found the fossils nine months later next to the explorers' frozen bodies.
The fossils
  • The fossils one was a piece of coal with beautifully traced leaves in layers and well-preserved impressions of thick stems.
  • They are remains of an extinct tree called Glossopteris, which may have grown 30 m tall.
Climate
  • Climate trees do not grow on Antarctica today because it is too cold around the South Pole.
  • The fossilised leaves are evidence that the land now called Antarctica once had a warmer climate,
    • so the continent must have been further north, away from the South Pole.
Same species elsewhere
  • Glossopteris fossils had already been found in Africa, Australia, India and South America, which suggests the continents were once joined together.
  • Its seeds were heavy and could not have been blown across oceans.

Section 3 of 8Evidence from animals

Mesosaurus
  • Mesosaurus a small freshwater reptile about one metre long, whose fossils are found in South America and southern Africa in rocks of the same age, around 270 million years old.
  • It could not have swum across the salty Atlantic Ocean, which is thousands of kilometres wide.
Lystrosaurus
  • Lystrosaurus an animal with just two teeth that used its beak to tear leaves from plants.
  • Its fossils have been found in Africa, India, Antarctica, China and Mongolia.
Cynognathus
  • Cynognathus its fossils are found in South America and Africa.
Joined land mass
  • Joined land mass the simplest explanation is that the continents formed a single land mass when the organisms lived, and the land later moved apart.

Section 4 of 8Rock strata and other matching evidence

Rock layers (strata)
  • Rock layers (strata) layers of the same type, age and sequence are found on opposite sides of the Atlantic, as if a single layered rock had been cut.
Mountain chains
  • Mountain chains the Appalachians in North America and the Caledonian mountains in Scotland and Norway line up when the continents are placed together.
Glaciers
  • Glaciers evidence of past glaciers on southern continents, now in warm climates, fits together when the continents are joined near the south pole.
Coastlines
  • South America and Africa fit like jigsaw pieces, especially when the edges of the continental shelves are used.

Section 5 of 8Interpreting a fossil map

Pattern
  • Pattern shaded areas where each species is found touch when the continents are joined,
    • such as Mesosaurus in a band across southern Africa and eastern South America.
Explanation
  • Explanation a freshwater animal could not swim the ocean, so a joined land mass is the best explanation.
Combining evidence
  • Combining evidence fossils of two species can show two continents were joined, for example India and Africa.

Section 6 of 8Evaluating the evidence

Land bridges
  • Land bridges critics of Wegener suggested land bridges once linked the continents and later sank,
    • but there is no evidence for such bridges on the sea floor.
Not enough alone
  • Not enough alone fossil evidence supports continental drift but is not sufficient by itself.
Mechanism
  • Wegener could not explain what force moves continents, so many scientists rejected his idea at first.
  • Stronger evidence came later from the sea floor and from measurements of plate motion.
Wording
  • Wording evidence supports a hypothesis rather than proves it.

Section 7 of 8Key terms

TermMeaning
Fossilthe preserved remains or traces of an ancient organism.
Stratalayers of sedimentary rock.
Continental driftthe slow movement of continents over geological time.
Pangaeathe supercontinent that existed about 250 million years ago.
Glossopterisan extinct seed fern whose fossils are found on several southern continents.
Mesosaurusan extinct freshwater reptile found as fossils in South America and Africa.

Section 8 of 8Exam technique

1
Saying Mesosaurus could swim the ocean — it was a freshwater reptile.
2
Thinking fossils move — the rock holding them moves with the continents.
3
Saying coastlines fit exactly today — the fit is best at the edge of the continental shelves.
4
Thinking one fossil alone proves the theory — several lines of evidence are needed.

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