Year 8 Science · Unit 3 · Lesson 20
Challenge Worksheet
Learning Goals
Read the graph
The bar chart below shows the density of each Earth layer. Study it carefully, then answer the questions.
Data: Dziewonski & Anderson (1981), Preliminary Reference Earth Model (PREM).
(a) Describe the overall trend in density shown in the chart.
(b) By approximately how many times is the inner core denser than the crust? Show your working.
(c) Explain why density increases toward Earth's centre. Use at least two scientific ideas in your answer.
Evaluate the claim
Someone claims…
"We have never drilled deeper than 12 km into Earth (the Kola Superdeep Borehole, Russia), yet scientists claim to know exactly what Earth's interior looks like, including a solid inner core and a liquid outer core thousands of kilometres down. This is just guesswork. Without direct samples, we can't really be sure."
(a) What part of this claim is accurate? Is it true that we have never drilled deep enough to sample Earth's mantle or core?
(b) What is misleading about the claim that scientists are just "guessing"? Describe at least two specific types of seismic wave evidence that give us reliable information about Earth's interior.
(c) What additional evidence or information would make scientists even more confident about Earth's interior structure? Suggest one type of evidence not yet mentioned.
1. The Jack Hills of Western Australia contain zircon crystals aged 4.4 billion years, the oldest known geological material on Earth. What does this tell us about the Australian continental crust compared to oceanic crust?
2. Earth's magnetic field protects us from solar radiation. Using what you know about Earth's structure, explain which layer produces this field and why it is able to do so.
Wrap Up
In one sentence, what was the main idea of this lesson?