When planning for teaching in your classroom, it can be useful to see where a sequence fits into the larger picture of science. This unit is anchored to the Science Understanding core concepts for Earth and Space Sciences.

• The Earth system comprises dynamic and interdependent systems; interactions between these systems cause continuous change over a range of scales

Students have experienced this core concept before by examining daily and seasonal changes (Year 1), the properties of soils, rocks, and minerals (Year 3), and the water cycle (Year 4). In Year 5, this core concept involves explaining how weathering, erosion, transportation, and deposition cause slow or rapid change to the Earth’s surface.

This core concept is linked to the Key Science Ideas:

• Energy (kinetic movement of water, thermal heat energy) moves through and can cause observable changes to the Earth's surface. (Systems)
• The stability of the Earth's surface can be disrupted by sudden changes or gradual changes over time. (Stability and change)
• Patterns of change on the Earth's surface can be used to identify cause-and-effect relationships and make predictions. (Patterns, order, and organisation)
• Some patterns of change on the Earth's surface have an underlying cause that cannot be observed at the same spatial or temporal scale. (Patterns, order, and organisation)
• Models can be used to investigate relationships between components of systems. (Systems)

When your students next progress through this Core Concept, they will investigate the rock cycle and tectonic activity (Year 8).

Taking account of students’ existing ideas is important in planning effective teaching approaches which help students learn science. Students develop their own ideas during their experiences in everyday life and might hold more than one idea about an event or phenomenon.

Some students might believe that landforms do not change over time, that the rivers are dug out by God or man, or that it is the wind that makes rivers flow. However, landscapes are ever changing through weathering, erosion, transportation, deposition and human activities.

Students often think that soils have always existed. This is because the rates at which soils form can appear to be very slow to students. For example, untended house gutters may develop a thin layer of soil over a few years.

Students might think that rocks are hard and unchangeable because in their lifetime little natural change is visible. This is reinforced by expressions in everyday language such as ‘hard as a rock’. However, some rocks might crumble easily, for example, sedimentary rocks that are made of sand, shells and pebbles that are compressed together. All rocks are susceptible to changes due to weathering; harder rocks tend to weather more slowly. Over the life of planet Earth, its rocks have changed many times.

Students might think that the Earth’s crust consists mainly of soil with some rocks embedded in it. However, the Earth’s crust is primarily rock, with a thin layer of soil on top which varies in thickness.

In this sequence students are given the opportunity to consider the different timescales over which weathering and erosion occur. By Year 5, a student’s ability to understand relative size and rates of change is developing, and they can understand that events and phenomena that change the Earth’s surface can occur rapidly within hours or slowly over thousands and millions of years.

Over the course of this sequence students will explore and make models of weathering and erosion processes to further their understanding, culminating in exploring a solution to a local problem caused by weathering or erosion.

The images used in the Thinking about landscapes Resource sheet can be swapped for local examples showing similar weathering and erosion issues. Outlined below is a guide for what you might look for if selecting your own images to include.

Questions 1 & 2

These questions are designed to activate students’ prior knowledge on rocks and soils covered in Year 3. The questions also provide opportunities to model how to collate and write generalisations about the responses. They are non-specific and should be suitable for students in various contexts. However, if you are (for example) living in a rural farming community where students have a deeper knowledge of soil composition, the questions may be augmented and added to.

Question 3

In this question students are prompted by an image of a river bank that has been eroded after heavy rain. This image could be replaced with any example of erosion caused by water such as eroded coastlines, muddy run-off, bare patches of dirt where topsoil has been washed away, or rills/gullies formed on hillsides.

Question 4

This question shows an example of physical (also called mechanical) weathering. The London Bridge arch was broken down over time by the pressure of repeated waves crashing against it. Whilst there is a small component of chemical weathering involved (due to the salinity of the ocean’s waters), chemical weathering causes a change in the composition of the rock, which is not the case here. The arch simply crumbled into the sea due to the force of the waves.

If using a local example, look for one where rocks have been broken up by physical forces. This might include rocks cracked open by freezing and thawing water or tree roots. It can also include rock worn down, or into unusual shapes, through the abrasive force of wind.

Question 5

This question shows an example of chemical weathering, from Katter Kich (or Wave Rock) in Western Australia. Slightly acidic rainwater ran into cracks and crevices in the rock, reacting with the granite the rock is made from and breaking it down from within. This made it vulnerable to further erosion and dissolving.

If using a local context, look for examples where chemical reactions have created unusual shapes, such as pits and cavities in rock surfaces. Rust appearing on rocks is also caused by a chemical reaction to iron oxide in the rock.

Question 6

In this question, students are prompted by an image of Uluru and asked to think about what it may look like 5000 years into the future. This will help determine if students understand the slow timescale of weathering. Any local rock formation that students know of can be substituted if using a local example.

Connections to local First Nations peoples

Many rock formations and natural areas carry special significance for the First Nations peoples of the area in which they are found. They may have specific Dreaming or traditional stories attached to their creation and future, or be sites of cultural significance that it is not appropriate to talk about in the classroom. Where possible, consult with the local First Nations Elders or Education Officers to discuss the protocols for what is appropriate for your area, and the possibility of enriching student understanding by sharing appropriate local knowledge.

Weathering and erosion causes the surface of the Earth to constantly change.

Some of these changes, such as changes to rock faces and formations, happen very slowly over hundreds or even thousands of years. Others, such as the erosion of topsoil on farmland or the changing of coastline, also happen slowly but may be visible during our lifetimes. Catastrophic events such as floods and landslides can cause rapid and sometimes devastating change.

Below are some geological terms used in this sequence. As this is the first time students will have encountered these concepts in the curriculum, the terms ‘weathering’ and ‘erosion’ are introduced in basic sense during this lesson. Subsequent lessons should support students to deepen their understanding of these terms and explicitly introduce others.

Weathering is the breaking up or wearing away of rocks or minerals, resulting in smaller rocks and rock particles. Weathering can be caused by chemical, physical or biological processes.

• Physical (also called mechanical) weathering involves physical actions that break down rocks or minerals into smaller pieces. For example, the expansion of frozen water might cause a rock to crack, waves crashing into rocks on the coast can create sea caves, and wind-blown sand can act like sandpaper, wearing away the surface of rocks over time.
• Chemical weathering is the breaking down of rocks and minerals through changes in the chemical composition of the material. For example, rainwater running over the surface of a rock will carry away particles of rock. It also softens the surface of the rock and leave it vulnerable to other forms of weathering. Chemical weathering is impacted by the pH (acidic or basic level) of the water and the rocks and minerals it is interacting with. The presence of oxygen can also play a part, particularly when iron is involved.
• Biological weathering occurs where living or once-living organisms contribute to both chemical and mechanical/physical weathering. For example, the growth of a tree root may cause a rock to crack, lichens and mosses secrete acids which break down rock, and burrowing animals can weaken rock structures.

Erosion is the process where a transportation agent (such as water, wind or gravity) moves soil, rocks, sediments and dissolved material from one location and deposits it in another.

• Water erosion comes in many forms and can be highly destructive. Even the splash of a single raindrop on bare soil can cause soil particles to rise as high as 60cm and to move up to 1.5m from the point of impact. Areas where there is little vegetation to hold the soil in place are vulnerable to having the top, most nutrient-dense layers of soil being washed away. As water travels along the surface it concentrates in depressions on the surface, forming ridges, or rills. These can eventually become gullies as the ridges get deeper. 
  And that’s just what's happening on the surface! Under the surface, water moves easily through poor soils, animal burrows or spaces left by decaying tree roots, undermining the surface and making it more vulnerable to mass movement events.
• Wind erosion occurs when the force from the wind detaches soil and sand particles and carries them away. Dry and sandy soils are the most vulnerable to wind erosion, which is worsened in strong and persistent winds. A lack of vegetation and ground cover, which leaves soil and sand exposed, also worsens wind erosion. Exposure of soil can be caused by deforestation, land clearing for construction, large numbers and overgrazing of animals, and intensive farming. Exposure of sand occurs when vegetation is removed or washed away from beaches and sand dunes during high tides, especially when exacerbated by storms. Wind erosion can cause dust and sand storms.

Transportation is the movement of weathered and eroded material across the Earth’s surface, carrying sediments (small rocks, sand and soil away) from their source to a new location. Transporting agents include wind, water in all its forms (rivers, rainwater runoff, ocean waves, ice, snow) and gravity.

Deposition is the laying down of sediment carried by wind, water or gravity in a new location.

Sediments are the solid matter (small rocks, sand and soil) that do not dissolve and are transported from and deposited in a new location.

Weathering

Weathering is a natural process that has occurred since the Earth was formed. It is a vital part of creating the Earth's ecosystems and occurs over a long time scale, so it is almost impossible for students to observe as it occurs in-situ.

When looking for evidence of weathering in the local area you might observe:

Physical weathering

• Rock fragments: Look for broken/smaller pieces of rock at the base of a larger rock.
• Cracks: Observe cracks in rocks causes by the growth of tree roots, or water freezing and thawing.
• Exfoliation: Look for peeling or scaling rock surfaces.
• Rounded/smooth edges/surfaces: Notice how rocks become rounded and smooth over time due to wind, water or ice.

Chemical weathering

• Discolouration: Look for changes to rock colour. A common one is rust formed by oxidation of iron present in the rock.
• Softening/crumbling: Rocks that are easily crumbled can be a sign they have been dissolving or reacting to chemicals in air/water.
• Pits and cavities: The formation of pits and cavities in rock surfaces can be an indication of dissolving.

Biological weathering

• Root penetration: Look for tree roots growing into cracks and crevices in rocks.
• Animal burrows: See if there are any burrows created by animals, which have exposed otherwise covered rocks to weathering processes.
• Organic acids: Look for the presence of plants, such as moss and lichens, that can produce acids that decay the rock.

Erosion

Erosion is also a natural process that helps move organic matter around the Earth's surface. It too can take a long time, but it can also happen rapidly due to weather events. Human activities such as deforestation, construction, agriculture and mining can have a more noticeable impact on the rate of erosion.

When looking for evidence of erosion in the local area you might observe:

• Devegetation: Areas where vegetation has been removed and topsoil left exposed. It will often occur near construction sites, in agricultural areas, or even in the school garden. It can lead to exposed soil roots and gullies.
• Exposed soil: exposed topsoil is much more easily blown or washed away, revealing bare patches.
• Bare patches/spots: Look for areas where the topsoil has been removed and bare dirt is exposed. Plants often do not grow in these areas because there are not enough nutrients to support their growth.
• Exposed roots and leaning trees: Exposed roots often means erosion, and can mean the soil is unstable, leading to falling or tilting trees.
• Gullies: Channels formed by running water that often indicate the removal of topsoil.
• Rills: Shallows gullies formed on the side of hills; also caused by run-off.
• Sedimentation: Muddy or discoloured water in streams and ponds often means sediment is being carried away.
• Cracks and depressions: Cracks or sunken areas in soil can form as soil is transported away.
• Cracks in buildings: This can mean the soils underneath has been eroded, causing the building to shift and crack.

Coastal erosion may also be characterised by:

• reduced sand volume.
• narrower beaches.
• lower beach slopes.
• creation or destruction of sandbars.
• decreasing dune size.
• exposed dune faces.
• undercutting of cliffs leading to the formation of arches and also rockfalls.
• landslides.

Weathering and erosion of man-made structures

Man-made structures such as buildings, roads and bridges can also be impacted by weathering and erosion.

Buildings might be affected by weathering and erosion causing minor and easily remedied issues such as peeling paint or cracking pavements. More serious issues might include damaging the foundation of the building, leading to cracking, structural damage and subsidence.

Stairs, especially those made of stone or bricks, can be worn away over time through use. Many staircases in historical buildings show this wear, with indents often formed in the centre of the steps after hundreds or even thousands of years of footsteps.

Roads can be eroded when the soil and/or pavement around the roads is washed away during/after heavy rainfall or worn away by excess traffic. Potholes, ruts, corrugations or even landslides can often be the result.

The structural integrity of bridges can be impacted by heavy rainfall, floods, debris flows, and landslides causing them to be unsafe.

Although not ideal, there are many reasons why it might be more convenient, practical and appropriate to use Google Maps or similar to undertake a virtual tour of your area to look for examples of weathering and erosion. These might include the accessibility of the local landscape, weather conditions, or simply supervisory capacity.

Google Maps has many features that can be utilised to support a virtual tour. See the image above to see how each feature will look on a desktop screen.

• Typing the specifically required location into the search box, located in the top left on a desktop screen, will give you an aerial overview of the area. You can use a specific address, a suburb name, or even the name of a whole region.
• Use the Layers feature, located in the bottom left of a desktop screen, to switch between views. Satellite view shows photographic aerial shots. Note that these images may be out of date.
• Use the Street View feature, found in the bottom right on a desktop screen, to see a 360° street-level view of a specific location. You can navigate along the roadway using the arrows or by simply tapping or clicking in the direction you'd like to move.
• Save or share images of a location using the Share icon located in the top right on a desktop screen.

The Question Formulation Technique (Santana & Rothstein, 2018) outlines four steps for students to generate, refine, and select useful questions. This includes:

1. Examine stimulus materials.
2. Brainstorm questions.
3. Improve questions: change closed questions or statements into open questions.
4. Prioritise questions according to importance, ability to be investigated, what will help with the Act phase, and how it will be answered.

Students should work together in small groups of 3-5.

An adaptation of the well-known KWL chart, a TWLH chart is a learning tool used to elicit students’ prior knowledge by asking what they Think they know, determine questions students Want to know answers to, document what has been Learned, and How students know they’ve learned. 

One of the key aspects of a TWLH chart is its ability to guide a student in metacognitive (the ability to think about your thinking) processes. By focusing on what students think they know, they are prompted to see learning as a journey, where new scientific evidence and experiences might change your thinking. This is a very important aspect of thinking scientifically.

In this instance, students are considering their initial knowledge of light. In this phase of learning, students should be encouraged to populate the T and W sections of the chart.