Year 8 Science · Unit 3 · Lesson 25

Weathering and Erosion

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Learning Goals

Classify a range of geological processes as physical, chemical, biological weathering, erosion, or deposition.
Apply weathering and erosion concepts to explain the formation of Uluru and the red colour of Australia's Outback.
Link chemical weathering to visible features of a real Australian landmark.

Warm Up

Sort it!

Write each process from the pool into the correct category column in the table below.

Freeze-thaw cracking in alpine rock Iron in sandstone reacting with oxygen to form rust Lichen producing weak acids on a gravestone River carrying sand grains downstream Sand settling on the seafloor Carbonic acid dissolving limestone Plant roots splitting a boulder Murray River depositing silt at its mouth Rock surfaces flaking due to daily heating and cooling Wind carrying dust across the Outback

Physical weathering	Chemical weathering	Biological weathering	Erosion	Deposition

Your Turn

Real-world context

Uluru (also known as Ayers Rock) rises 348 metres above the flat plain of the Northern Territory. It is made of arkose sandstone, the same type of rock as the surrounding plain. Geologists estimate that Uluru and the surrounding rock were once part of a vast sedimentary basin deposited around 550 million years ago. Over the following 300–500 million years, differential erosion removed the softer surrounding rock but left Uluru standing. Uluru's surface shows a distinctive orange-red colour and a hard outer crust, with flaking and rounded hollows visible near the base.

(a) Uluru and the surrounding flat plain are made of the same type of sandstone, yet Uluru still stands while the surrounding rock has been worn away. Explain why this occurred. What property of Uluru's rock allowed it to survive when the surrounding rock did not?

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(b) The flat surrounding plain was shaped mainly by which type of weathering? Explain your reasoning, referring to the arid (very dry and hot) conditions of the region.

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(c) Uluru's surface is a distinctive orange-red colour. Using your knowledge of chemical weathering, explain what has happened to the rock's minerals to produce this colour.

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Wrap Up

In one sentence, what was the main idea of this lesson?