HSC Earth and Environmental Science 2025

(a) [1 mark]. Coal. (Iron ore, gold, copper or bauxite are equally acceptable.)

(b) [2 marks]. During the planning phase, traditional owners can be engaged to survey the proposed site and share cultural knowledge of country, identifying sites of significance so the operation is designed to minimise damage to culture and heritage. This involvement, often through a land council, gives traditional owners an ongoing role in approvals and later land restoration.

Marker's note. Name a resource that is genuinely mined. For (b), link the involvement to a specific phase of operations (planning, mining, restoration or reclamation) and recognise the unique knowledge and connection to country that traditional owners contribute; use connected sentences rather than a single short phrase.

[3 marks]. Index fossils give a relative age. An index fossil is a species that was widespread but existed only for a short, well-defined interval of geological time. If such a fossil is found in a rock layer, the layer must have formed during that same narrow interval, so it is given the index fossil's age. This is supported by the principle of superposition, that in undisturbed strata each layer is younger than the one below it.

Marker's note. Make clear that the method gives a relative (not absolute) age and link it directly to how it dates the layer. A labelled diagram of superposition helps. Avoid confusing rock-layer dating with unrelated climate proxies.

[3 marks]. Fire-stick farming is a controlled-burning process used to manage the land and its resources. Low-intensity burns are lit at the right season to clear undergrowth, which reduces fuel loads and the risk of severe bushfire, and encourages fresh growth that attracts game and supports food plants. Rotating the areas burnt allows each patch to recover, sustaining the resources over the long term. (Midden building, totemic systems and selective harvesting are also acceptable.)

Marker's note. Describe an actual management process in detail, not just name a resource. Show how the process sustains the resource over time.

[4 marks]. The Siberian Traps were vast flood-basalt eruptions that poured out lava over roughly a million years, releasing enormous volumes of sulfur dioxide and carbon dioxide. The sulfur dioxide caused short-term cooling, but the sustained release of carbon dioxide drove significant long-term global warming lasting far beyond the eruptions.

By contrast, the 1991 Mt Pinatubo eruption was a single, much smaller explosive event. Its sulfur dioxide formed a sulfate aerosol veil that produced a slight global cooling of a few tenths of a degree C for only a year or two, and it released too little carbon dioxide to cause meaningful long-term warming.

So both eruptions emitted climate-active gases, but the Siberian Traps drove large, lasting warming whereas Pinatubo caused only a brief, minor cooling.

Marker's note. Name the specific gases and link sulfur dioxide to cooling and carbon dioxide to warming. Contrast the time frames (millions of years versus a year or two). Avoid the misconception that the Traps caused an ice age.

(a) [2 marks]. Wear disposable gloves when handling the waste and wash hands thoroughly afterwards. Used waste can carry bacteria, mould and sharp items, so a barrier on the skin prevents contact with pathogens and reduces the risk of infection or injury.

(b) [4 marks].

1. After lunch each day, collect the bins from each area (classrooms, office, outdoor seating).
2. Tip each bin's contents onto a separate plastic sheet and sort into recyclable and non-recyclable waste.
3. Weigh the recyclable waste from each area on a kitchen scale and record the mass in kilograms in a table.
4. Repeat steps 1 to 3 each day for three weeks, keeping the collection time, equipment and sorting rules the same.
5. Average the recyclable mass for each area and compare to identify which areas produce the most recyclable waste.

Here the independent variable is the area of the school, the dependent variable is the mass of recyclable waste, and controlled variables include the collection time and sorting method. Repeating over three weeks improves reliability.

(c) [2 marks]. A recycling bin should be placed in the outdoor seating area shown on the map. This is where students eat lunch and discard drink cartons and food packaging, so a bin there captures the most recyclable items, increasing recycling and reducing the waste sent to landfill.

Marker's note. Write (b) as a numbered scientific method beginning each step with a verb, and clarify that "amount" means a measured mass, count or volume. Name the variables. Support the choices in (a) and (c) with reasoning and refer to the map in (c).

(a) [3 marks]. The independent variable (ocean floor depth) goes in the left column and the dependent variable (wavelength) in the right, with units in the headers:

(b) [4 marks]. A tsunami is a series of waves caused by displacement of ocean water, often by an undersea earthquake. In the deep ocean it has a very long wavelength (about 280 km at 7 km depth in Figure 2) but a small height, so it passes almost unnoticed and is not a disaster there. As it approaches the shore the ocean floor shallows; Figure 2 shows the wavelength shrinking sharply (to about 10 km at 0.05 km depth) and Figure 1 shows the wave height building dramatically as that energy is compressed into shallow water. The resulting tall, fast wall of water floods the coast, destroying infrastructure and endangering lives, which is why a tsunami becomes a disaster only when it reaches the shoreline.

Marker's note. Build the table correctly with the independent variable first, units only in the headers, and all six points transcribed from the graph. In (b) quote numerical data from Figure 2 and refer to Figure 1, and do not confuse wavelength with amplitude or call a tsunami a tidal wave.

[8 marks]

Planting native trees is highly effective for some course problems and only partly effective for others.

Problem 1: anthropogenic climate change

Burning fossil fuels for electricity adds excess carbon dioxide to the atmosphere, where it traps heat and drives global warming. As native trees grow they photosynthesise, capturing carbon dioxide and locking the carbon in their wood as a long-term carbon sink, and their transpiration cools the surrounding air. Judged against the criterion of measurable mitigation, tree planting is effective but limited: a single planting offsets only a small fraction of national emissions, so it works best alongside cutting emissions at the source rather than as a stand-alone solution.

Problem 2: land degradation from mine tailings

Mining produces large volumes of tailings that, if exposed, blow as dust and contaminate waterways. During mine reclamation the tailings dam is capped with topsoil and native trees are planted over it; their roots bind the soil, prevent erosion and contain the tailings, while also restoring habitat. Judged against the criterion of stabilising and rehabilitating the site, tree planting is very effective here, directly fixing the problem on the ground.

Overall, planting native trees is genuinely effective for stabilising degraded land and provides a real but partial contribution to mitigating climate change, so its effectiveness depends on the problem it is applied to.

Marker's note. Choose two genuine, unrelated course problems and make a clearly supported judgement against criteria for each, not a general description of trees in an ecosystem. Plan the response for logical flow and avoid the misconception that oxygen released by trees mitigates climate change.

[5 marks]

Sustainability means meeting present needs without compromising the ability of future generations to meet theirs.

Activity 1: pollution

Agricultural run-off, microplastics and industrial discharge add chemicals and litter to rivers and aquifers. This lowers water quality, harms aquatic ecosystems and can make the water unsafe for human use, so it has a strongly negative effect on sustainability, reducing the usable water available to future generations.

Activity 2: off-creek water storage

Taking water from rivers only during high-flow periods, when quality is good, and storing it for later use leaves enough flow in the river during droughts to sustain ecosystems. This has a positive effect on sustainability, securing supply for a community without degrading the resource.

So human activities can either undermine or support water sustainability: pollution degrades the resource for the future, whereas well-designed off-creek storage maintains it.

Marker's note. Focus on the key word "assess", giving a clear judgement and direction for each activity, and link both explicitly to sustainability with water treated as the resource.

[3 marks].

In short, humans lower atmospheric oxygen and raise carbon dioxide on a timescale of centuries, whereas cyanobacteria raised oxygen and lowered carbon dioxide over billions of years; more carbon dioxide drives warming and less drives cooling.

Marker's note. Give two contrasts in which the human and cyanobacterial effects are genuinely opposite (for example, humans decrease oxygen while cyanobacteria increase it), and name specific activities rather than just listing them. A table shows the contrast clearly.

[3 marks]. Compare the gaps between successive formations:

There is a consistent 600-million-year gap between the formation of each supercontinent. Pangaea formed 300 Ma BP, so the next supercontinent should form about 600 million years after that:

So a future supercontinent is predicted to form in approximately 300 million years from now.

Marker's note. Show the calculations by annotating the table, use "Ma BP" consistently, and state clearly that the timing is measured from the present day. Check the scale of time so the answer is plausible.

(a) [3 marks]. First, install rooftop solar panels, so the home draws less electricity generated from fossil fuels. Second, walk or cycle instead of driving for short trips, so less petrol is burnt. Both actions reduce the consumption of fossil fuels, which cuts the carbon dioxide emitted to the atmosphere; since carbon dioxide is the main greenhouse gas driving warming, each action lowers the individual's contribution to rising global temperatures.

(b) [4 marks]. Geo-engineering means deliberately intervening in the climate on a very large scale. One strategy is placing giant mirrors or a reflective shield in orbit to reflect a fraction of incoming sunlight back into space. The advantage is that, by reducing the solar energy reaching Earth, it could lower global temperatures quickly without needing to cut emissions first. The disadvantage is that it is enormously expensive and technically difficult to deploy at the scale required, and it treats the symptom rather than the cause, since atmospheric carbon dioxide keeps rising and would continue to acidify the oceans.

Marker's note. In (a) link each action to a specific greenhouse gas and to mitigating warming, and avoid actions that are really about waste or general sustainability. In (b) choose a genuine large-scale geo-engineering strategy and give a clear advantage and disadvantage tied to global temperatures.

[3 marks]. Doppler radar sends out radio pulses that reflect off raindrops in a storm. From the returning signal it measures how far away the rain is, how heavy it is, and, using the Doppler shift, how fast the air is moving toward or away from the radar. Detecting intense rainfall and strong rotating winds lets forecasters predict short-term extreme events such as flash floods and severe thunderstorms in the next few hours, so warnings can be issued.

Marker's note. Recognise that "meteorological" means weather, not meteorites. Name a specific technology (for example Doppler radar, satellite or barometer), explain what it measures and link that to predicting a named short-term extreme weather event.

(a) [3 marks]. The focus is the point underground where the rock ruptures. At a divergent or transform boundary the brittle crust is thin and near the surface, so the rock fails at shallow depth, giving a shallow focus. At a convergent boundary, an ocean-continental subduction zone, one plate is driven down into the mantle along the subducting slab; the slab stays cold and brittle to great depth, so stress builds and ruptures far below the surface, giving a deep focus. The depth therefore depends on how deep brittle rock is being stressed at that boundary.

(b) [4 marks]

Factor 1: focus depth

A deeper focus means seismic waves travel through more rock before reaching the surface, so their energy disperses and the ground shaking at the surface is weaker, causing less damage. A shallow focus delivers stronger shaking directly beneath the building and more damage.

Factor 2: ground type

A building on loose, water-saturated sediment is far more vulnerable than one on solid bedrock. Shaking can cause the saturated grains to behave like a liquid (liquefaction), so the building tilts, cracks or sinks. The same building founded on bedrock transmits the shaking with little settling and survives with less damage.

Marker's note. In (a) name the boundary types (for example ocean-continental convergent and subduction) and link them to focus depth. In (b) analyse two factors that genuinely affect building damage and support each with a clear annotated diagram; keep the response about earthquakes, not tsunamis or landslides.

[8 marks]

The breakup of Rodinia and the assembly of Pangaea are two halves of the plate tectonic supercycle.

Breakup of Rodinia

Sitting over the mantle, the large continent Rodinia acted as an insulating lid, trapping mantle heat beneath it. The heat built up until a mantle plume of hot, less-dense magma rose and domed the crust, stretching and thinning it until it rifted. As the rift widened, magma erupted to form new oceanic crust at a divergent boundary, and a mid-ocean ridge developed at the centre of a growing ocean basin. Rodinia split into smaller continents that drifted apart on the spreading sea floor.

Formation of Pangaea

The new oceanic crust cooled, became denser and, where the dispersing continents began to converge again, started to subduct beneath the leading edge of a continent at a convergent boundary. Subduction consumed the intervening ocean basin, drawing the continents together. When the ocean had finally closed, the continents collided, their crust crumpling into mountain belts and welding the landmasses into the single new supercontinent Pangaea.

Marker's note. Account for both a reason for Rodinia's breakup (mantle plume driving rifting) and a reason for Pangaea's formation (subduction then collision), and recognise the second supercontinent is a different landmass. Use clear, labelled cross-section diagrams with arrows for plate movement and refer to them. Avoid the misconception that ocean currents drive plate tectonics.

(a) [2 marks]. Under the present climate, Graph 1 shows the North Atlantic Ocean has a relatively high water density with only a moderate volume of freshwater input from melting sea ice, so the salty, dense surface water can sink and drive the overturning current.

(b) [4 marks]. A flow chart starting with the melting of sea ice:

Melting sea ice
-> Increased freshwater input lowers the salinity and density of the North Atlantic surface water (Graph 1)
-> The less dense surface water sinks less readily, so the NADW overturning current weakens (Graph 2)
-> Less warm water is drawn north along the conveyor belt
-> The climate in Europe cools (Graph 2)

(c) [2 marks]. A weakened overturning current and the resulting cooling of Europe would expand winter ice and snow cover, increasing the frequency of blizzards and extending cold-climate habitats for species such as polar bears, while shortening growing seasons for agriculture across northern Europe.

Marker's note. In (a) read Graph 1 for the present climate without inferring a time scale. In (b) build a logical flow chart with arrows, beginning with melting sea ice and referring to both graphs; remember melting sea ice does not directly raise sea level. In (c) explain a genuine flow-on effect and avoid circular reasoning or assuming Europe warms.