Year 8 Science · Unit 3 · Lesson 21
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Learning Goals
Because… chain
Fill in the missing effects. Each cause leads to the next step in the formation of a volcano at a subduction zone.
Overall outcome:
Real-world context
When Alfred Wegener presented his continental drift hypothesis to the Geological Association in Frankfurt in 1912, the audience was largely hostile. Scientists demanded he explain how continents could move through solid ocean rock. He had no answer. By the early 1960s, Harry Hess's seafloor spreading hypothesis, supported by paleomagnetic stripe patterns on the ocean floor, finally provided the mechanism Wegener was missing. In 1968, the theory of plate tectonics was formally established.
(a) Describe two specific pieces of evidence that Wegener used to argue that the continents were once joined. For each, explain why the evidence is persuasive.
(b) Why did scientists doubt Wegener even when his evidence seemed strong? What was missing from his hypothesis?
(c) What was the key evidence from the 1960s that convinced the scientific community? Briefly explain what seafloor spreading or paleomagnetism showed.
1. Australia moves approximately 7 cm north per year. Calculate roughly how far Australia will have moved in 1 million years. Express your answer in kilometres. Show your working.
2. Coal deposits have been found in Antarctica. Explain what this tells us about Antarctica's past position and how plate tectonics accounts for this.
Wrap Up
In one sentence, what was the main idea of this lesson?