HSC Earth and Environmental Science 2024

[2 marks]. Composting is a strategy for managing solid food and green waste. Organic material such as grass clippings, leaves and food scraps is collected separately, then microorganisms break it down under controlled moisture and oxygen into a nutrient-rich compost. This diverts biodegradable waste from landfill and returns the product to soils. (Kerbside recycling, e-waste collection or incineration are equally acceptable named strategies.)

Marker's note. Name a genuine strategy and outline the process it follows (how the waste is handled), not just the outcome. Choose an example that is easy to describe.

[4 marks]. Resource: copper. Copper is presently used worldwide as the main conductor in electrical wiring, motors, generators and electronics because it conducts electricity efficiently and resists corrosion. In the future its use is very likely to grow sharply: the transition to renewable energy and electric vehicles depends on copper for wind turbines, solar arrays, batteries and grid wiring, all of which use far more copper than fossil-fuel equipment. Because copper is a finite, non-renewable resource and rich ores are being depleted, its value will rise and recycling and lower-grade ores will become increasingly important. Overall, copper is a critical resource now and will become even more in demand and more valuable as electrification expands.

Marker's note. Treat copper (or your chosen item) clearly as a resource, outline both present and likely future use, and make a specific judgement ("demand and value will rise because of electrification"), not an implied one. Stay focused on the key word "assess".

(a) [4 marks]. Mount Ruapehu sits at a convergent (subduction) boundary. The denser oceanic Pacific Plate is subducted beneath the less dense Australian Plate (the plate-movement arrows on the map show the plates converging). As the subducting slab descends into the hotter mantle, water released from it lowers the melting point of the overlying mantle, generating magma. This magma is less dense than the surrounding rock, so it rises through the overriding Australian Plate. Reaching the surface, it erupts repeatedly, building the layered stratovolcano that is Mount Ruapehu.

(b) [4 marks]. Mount Ruapehu erupts viscous, gas-rich magma, so it is explosive. Two likely hazards are:

1. Lahars. The summit holds a Crater Lake. An eruption can eject hot rock and ash into this water, and the mix of water, ash and rock surges down the valleys as a fast, dense volcanic mudflow (the map marks past lahar paths). Lahars bury and destroy everything in the valley, including ski-field structures and roads.
2. Pyroclastic flows. Because the high-viscosity magma traps gas under high pressure, a sudden release can produce a pyroclastic flow, a ground-hugging current of superheated gas, ash and rock fragments that races down the slopes at high speed, incinerating and burying anything in its path. (Ash fall is also acceptable.)

(c) [4 marks]. Both measures help, but only to a limited extent, because they protect visitors only if visitors act on them. Hazard mapping (Figure 2) lets the Department of Conservation define risk-management zones, for example the advice not to camp within 1.5 km of the summit and not to enter the highest-risk Crater Lake area; this keeps visitors out of the most dangerous valleys and lahar paths. Public education (Figure 3) communicates simple, picture-based instructions, for example moving out of a valley up to a ridge top, or sheltering behind a bank and covering the head with a pack. The pictures make the response clear even to non-English speakers, increasing the chance visitors react correctly. However, the protection is partial: an eruption gives little warning, lahars travel very fast, and both measures fail if visitors ignore the zones or do not read the signs. So mapping and education substantially reduce, but cannot eliminate, the risk to visitors.

Marker's note. In (a) link a sequence of processes (subduction, melting, magma rise, eruption) to the map and name the boundary symbols. In (b) distinguish the composition of the hazards (lahars versus pyroclastic flow versus ash) and explain how each forms and harms. In (c) make explicit references to both figures and a judgement about effectiveness, including the limits (visitors must comply).

[3 marks]. Rising sea levels permanently submerge land that was previously intertidal or low-lying coastal habitat. As the water deepens over these areas, species that lived there (for example intertidal molluscs or mangroves) can no longer survive in the now permanently flooded zone, so their geographic range shifts. They must migrate landward and upward to colonise newly suitable habitat higher up the shore, changing where the species is found. Where there is no higher ground to move into (a coastal barrier or cliff), the species' distribution contracts. The cause (deeper water from sea-level rise) therefore drives a clear, directional change in the location where the species can live.

Marker's note. Address "distribution" specifically, a change in the location or area where a species is found, not changes to abundance, food chains or survival rates. Show a clear cause-and-effect link, and keep the impact of sea-level rise distinct from its cause (melting land ice).

[3 marks]. A local council green-waste (FOGO) kerbside bin is a community initiative that sustainably manages the resource of organic matter and landfill space. Households place grass clippings, prunings and food scraps in the bin; the council composts this material and returns it as a soil conditioner. This reduces the volume of biodegradable waste sent to landfill, extending the working life of the landfill site so it remains available for future generations, while the compost returns nutrients to soils now. Meeting present needs (waste disposal and soil improvement) without exhausting the landfill resource for the future is exactly what sustainability means.

Marker's note. Name the resource, describe the specific actions of the community initiative, and establish a clear link to sustainability (meeting present needs without compromising the future). Keep renewability, recycling and sustainability distinct, and elaborate on the key words rather than repeating "resource" or "sustainably".

[5 marks].

Both methods are justified because they target the cause of the concern (exposed material) rather than only the symptom, and so are effective and lasting.

Marker's note. Identify environmental concerns that are genuinely those of non-operational (abandoned) mines, not operating ones. Describe appropriate reclamation methods and justify each with cause-and-effect language, showing why the method is valid and effective.

[4 marks]. Cultural burning uses frequent low-intensity fires that support sustainability by keeping the land healthy for current and future generations. In the low-intensity diagram, the fire removes only fine fuels and ladder fuels while the canopy survives, the bark thickens, nutrient-rich mineral soil is exposed and new plants regenerate, with ongoing carbon capture. By contrast, the high-intensity fire diagram shows the canopy destroyed, nutrients lost, water-resistant ("hydrophobic") soil and ash, with little carbon capture. By burning often at low intensity, cultural burning reduces the build-up of fuel and so reduces the frequency and severity of damaging high-intensity bushfires. This protects the soil structure and nutrients, which take hundreds of years to recover after a high-intensity fire, and maintains healthy, regenerating vegetation that keeps capturing carbon. Because it preserves the soil and ecosystem for the future while caring for Country now, cultural burning is an important sustainable land-management process.

Marker's note. Refer explicitly to both diagrams (low versus high intensity), avoid generic "fire" language by naming the type of burn, and demonstrate a clear understanding of sustainability with a future value, linked to cause and effect.

(a) [3 marks]. Areas near plate boundaries (a tectonic setting of high seismic activity, like Christchurch) experience frequent, strong earthquakes, while areas far from boundaries (intraplate settings) have low earthquake risk. In the high-risk setting, strict building codes are justified because they require structures engineered to withstand strong ground shaking, which prevents collapse and saves lives; the Christchurch rezoning, which now bans construction on the liquefaction-prone river sediments, shows codes responding to local risk. In a low-risk setting, applying the same expensive standards is unjustified, so lower (cheaper) standards are acceptable. Matching the code to the level of risk therefore minimises earthquake impact where it is needed without wasting resources where it is not.

(b) [3 marks]. Base isolation is a building technology that reduces earthquake damage. Large flexible bearings, for example layered rubber-and-steel pads, are installed between a building's foundations and its superstructure. During an earthquake these isolators flex and absorb much of the horizontal ground motion, so the building above moves far less than the ground beneath it. This greatly reduces the forces transmitted into the structure, so walls and frames are not overstressed, the building stays standing and the people and contents inside are protected. (Houses built on stilts to keep living areas above flood levels is an equally acceptable example for a different disaster.)

Marker's note. In (a) link both high and low earthquake risk to their tectonic settings and justify the need for different codes (respond to plural "settings" and "codes"). In (b) describe an actual structural or engineering building technology (base isolators, stilts), not a predictive warning technology, and explain how it reduces damage.

(a) [1 mark]

To provide a sense of scale, so the size of the trace fossils can be judged.

(b) [2 marks]

A trace fossil records activity, not the organism itself. The worm burrowed through soft sediment, leaving an open burrow. After the worm left, the burrow filled with a different sediment (e.g. mud or sand). Over long periods this sediment was buried, compacted and cemented (lithified) into rock, hardening into a cast that preserves the shape of the original burrow.

(c) [3 marks]

Relative dating is suitable here: these trace fossils sit in sedimentary rock, so by the law of superposition they are younger than the strata below and older than those above, letting their age be placed relative to other layers and any index fossils present. Absolute dating is less directly suitable: radiometric dating measures the decay of radioisotopes in igneous rocks (such as volcanic ash), not in the sedimentary rock that holds the burrows. It can still be applied if a datable volcanic ash layer lies just below or above the trace fossils, bracketing their age numerically. So relative dating gives an order directly, while absolute dating gives a numerical age only indirectly, when suitable igneous material is nearby.

Marker's note. In (b) describe the steps that genuinely form a trace fossil (infilling then lithification), distinguishing them from body-fossil formation, and name the process. In (c) outline the technique of each dating method, not just the outcome, and explain its suitability; do not confuse "suitability" with "sustainability".

(a) [1 mark]

Increasing ocean temperatures (causing coral bleaching). (Cyclones, pollution, ocean acidification or rising sea levels are equally acceptable.)

(b) [2 marks]

The state of the reef and its resilience are positively related: a reef in good health (high coral cover, high diversity and biomass) has high resilience, so it can recover after a disturbance. As the reef's health declines, its resilience also falls, so it is less able to recover and is more likely to be pushed into a degraded state by further disturbance.

(c) [2 marks]

The fall in "peak" reef health is caused by the rising number, frequency and intensity of disturbances shown on the graph's horizontal axis. Each disturbance (such as a bleaching event or cyclone) reduces the reef's ability to function and recover. As disturbances become more frequent, the reef has too little time to recover between them, so its health is driven progressively lower and the achievable peak health falls. The reason is therefore the accumulating impact of more frequent and intense natural and human disturbances.

Marker's note. In (b) state the direction of the relationship (health and resilience rise and fall together) by reading the graph. In (c) "propose a reason" requires a justification linked to the infographic (more frequent disturbances leave less recovery time), not just naming a disturbance.

[4 marks]. A good index fossil must be from a species that is distinctly identifiable, geographically widespread, abundant, and confined to a short interval of geological time, so its presence pins down a precise age. Judged against these criteria, Archaean stromatolites are poor index fossils. They are biosedimentary structures built by colonies of small, soft-bodied cyanobacteria rather than a single distinctly identifiable species, so they cannot mark one narrow time interval. They are found in only a few locations globally, so they are not widespread, and stromatolite-forming cyanobacteria persisted over an enormously long span of geological time (billions of years) rather than a brief interval. Because they fail the key criteria of being distinctly identifiable, widespread and restricted to a short time range, stromatolite fossils are not useful as index fossils, even though they are valuable evidence of early photosynthetic life.

Marker's note. Identify several criteria for index fossils and apply each to stromatolites to reach a clear judgement. The geological range refers to the species, not one organism's lifespan, and a fossil is the preserved evidence of a once-living organism. Avoid irrelevant material such as radiometric dating or the origin of organic molecules.

(a) [3 marks]

The frequency of El Niño and La Niña events is similar before and after 1960: both periods show events crossing the thresholds at roughly comparable intervals, so the number of events per decade is about the same. The intensity, however, has increased after 1960. Before 1960 the temperature differences mostly stayed within about plus or minus 2 degrees C, whereas after 1960 several El Niño events exceed +2 degrees C (and the strongest reach around +3 degrees C), higher than any event before 1960, and the strongest La Niña events are also more negative. So while frequency is broadly unchanged, the events have become more intense since 1960.

(b) [7 marks]

El Niño adaptation - shift to water-efficient agriculture. El Niño brings drought and higher temperatures to eastern Australia, reducing water supply, drying soils (raising erosion and dust-storm risk) and causing crop failure and livestock loss. An effective adaptation is to change farming practice during the dry phase: replace water-intensive crops such as rice and cotton with low-water crops, and replace flood irrigation with targeted drip irrigation. This is justified because it directly conserves the scarce water resource, keeping crops and livestock viable through the drought rather than failing, and reduces the bare-soil erosion that El Niño dryness causes. (Building desalination plants or using recycled water for irrigation are also valid.)

La Niña adaptation - flood-risk rezoning and building controls

La Niña brings heavy rainfall and cooler temperatures, causing flooding, soil and river erosion, infrastructure and crop damage, and health problems from contaminated water. More intense rainfall floods areas that were previously low risk. An effective adaptation is to update flood-risk maps to include these newly vulnerable areas and change building codes to restrict construction on the floodplain (and relocate critical infrastructure to higher ground). This is justified because it removes people and property from the path of the floodwaters before the next La Niña, preventing the loss of life and the repeated rebuilding costs that come from building in newly high-risk zones.

Both strategies adapt to the impacts of the phenomenon (managing scarce water in El Niño, removing exposure to floods in La Niña) rather than trying to prevent the climate pattern itself.

Marker's note. In (a) use specific numerical data from the graph and explicitly address both frequency and intensity; if you tabulate, keep the table in context. In (b) provide a genuine adaptation (managing the impacts) for each of El Niño and La Niña, not a mitigation strategy, give multiple effects beyond those stated in the stem, and justify each strategy with reasons. Anthropogenic climate change is not required.

[8 marks]

Two examples show how changes in one sphere cascade through the others and affect humans.

1. Development of photosynthetic life

Photosynthetic cyanobacteria evolved in the biosphere during the Archaean. Using solar energy, they drew carbon dioxide from the atmosphere and released oxygen into the hydrosphere and atmosphere (the Great Oxidation Event). This rising oxygen reacted with dissolved iron, depositing banded iron formations in the geosphere (the iron ore humans now mine), and oxygen in the upper atmosphere formed the ozone layer, which absorbs ultraviolet radiation. The flow-on effects for humans are large: the ozone shield made the land habitable and protects people from UV damage and skin cancer, and the iron ore underpins modern industry. So a biosphere change reshaped the atmosphere, hydrosphere and geosphere and directly benefits humans today.

2. The Industrial Revolution and natural resources

Over the Carboniferous and Permian, organic matter from the biosphere was buried and altered within the geosphere to form coal. Humans extract and burn this coal, which powered the Industrial Revolution and raised living standards by providing abundant, cheap energy and employment (a human use of a geosphere resource). However, burning coal returns carbon dioxide to the atmosphere faster than natural processes remove it, enhancing the greenhouse effect. The warming atmosphere heats the hydrosphere (thermal expansion and ocean warming) and melts the cryosphere (glaciers and sea ice), raising sea levels that threaten coastal human settlements and ecosystems in the biosphere. Here a human activity (resource use) drives a chain of changes through the geosphere, atmosphere, hydrosphere and cryosphere that feeds back onto humans.

Both examples show the spheres as a connected system: a change in one sphere, whether driven by life or by humans, produces dynamic flow-on effects across the others and shapes the conditions for human life.

Marker's note. Analyse changes in one sphere and the resulting changes in others, with specific course examples and several dynamic links and flow-on effects, and connect them explicitly to human activities. Plan the response (paragraphs, subheadings or diagrams) and avoid the common confusion between ozone depletion and the greenhouse effect. Not every sphere need be covered.

[4 marks]. Climate. Sunlight is more intense at lower latitudes, so as Australia drifted north towards the equator its climate warmed and dried. The separation from Antarctica also opened the Southern Ocean, allowing the cold Antarctic Circumpolar Current to form, which isolated Antarctica's cold air and reinforced the warming and drying of the Australian continent. The result was an expansion of arid country, including the central deserts.

Evolution. This climate change drove evolutionary change in the biota. Cool-adapted Gondwanan rainforest shrank, and drought-adapted vegetation such as eucalypts and acacias spread. Among animals, large cold-climate megafauna (for example Diprotodon) became extinct as the continent warmed and dried, while smaller, heat- and drought-tolerant marsupials and reptiles flourished and diversified to fill the arid environments. So Australia's northward movement both warmed and dried its climate and reshaped which species could survive and evolve.

Marker's note. Explain changes to both climate and evolution with integrated examples, and show clear cause-and-effect (northward drift to warmer/drier climate to extinction of cold-adapted fauna and spread of arid-adapted species). Demonstrate genuine understanding of both climate and evolution, not one at the expense of the other.

[4 marks]. The meteorites/panspermia hypothesis proposes that the organic molecules needed for life did not form only on Earth but arrived from elsewhere in the solar system, delivered on meteorites. The existing evidence for it includes carbonaceous meteorites (such as the Murchison meteorite) found to contain amino acids and other organic molecules, showing such molecules can form and survive in space and reach Earth. New evidence from Perseverance could complement this in two ways. First, if the rover detects organic molecules in Martian rocks, it shows the same building blocks of life form on another planet, strengthening the idea that organic molecules are widespread in the solar system and could seed multiple planets. Second, if it finds possible microfossils or biosignatures, it would support the possibility that life or its precursors arose beyond Earth and could be transferred between planets on meteorites from a common source. In both cases the Mars data would not replace but reinforce the meteorite evidence, showing how new evidence is used to support and extend an existing scientific hypothesis.

Marker's note. Show in-depth understanding of the meteorites/panspermia hypothesis and the existing evidence (organic molecules in carbonaceous meteorites), and explain how new evidence from Mars could support it. Address all components of the question and distinguish this hypothesis clearly from other origin-of-life hypotheses.