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WACE ATAR Earth & Environmental Science study materials
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WACE ATAR Earth & Environmental Science practice questions

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Question 1Earth systems and the geosphere

Which layer of Earth's interior is composed mainly of liquid iron and nickel?

  1. The inner core
  2. The lower mantle
  3. The continental crust
  4. The outer core Correct answer.

Explanation

Seismic evidence shows that shear waves cannot pass through the outer core, indicating a liquid layer. This liquid layer lies between the solid inner core and the mantle and is dominated by iron and nickel. Its convection generates Earth's magnetic field.

Question 2Earth systems and the geosphere

The Mohorovicic discontinuity marks the boundary between which two regions?

  1. The outer core and the inner core
  2. The mantle and the outer core
  3. The crust and the mantle Correct answer.
  4. The lithosphere and the asthenosphere

Explanation

The Moho is defined by an abrupt increase in seismic wave velocity, reflecting a change from lower-density crustal rock to denser mantle rock. It lies at roughly 5 to 10 km depth beneath oceans and 30 to 70 km beneath continents. It is a compositional boundary rather than a mechanical one.

Question 3Earth systems and the geosphere

Which observation provided the strongest early evidence that Earth's continents have moved over time?

  1. Matching fossil and rock sequences on now-separated continents Correct answer.
  2. The measured thickness of continental crust
  3. The presence of liquid water on the surface
  4. The daily rotation of Earth

Explanation

Identical fossils and continuous rock formations found on continents separated by wide oceans imply the landmasses were once joined. This matching evidence, along with fitting coastlines, supported continental drift. Later seafloor spreading data confirmed the mechanism.

Question 4Earth systems and the geosphere

At a mid-ocean ridge, new oceanic crust is generated by which process?

  1. Friction melting along a transform fault
  2. Decompression melting of rising mantle rock beneath the rift Correct answer.
  3. Subduction of oceanic lithosphere into the mantle
  4. Partial melting of continental crust above the ridge

Explanation

As mantle material rises beneath a divergent boundary, pressure falls while temperature stays nearly constant, causing decompression melting. The resulting magma rises and solidifies to form new oceanic crust. This process builds the ridge and drives seafloor spreading.

Question 5Earth systems and the geosphere

A convergent boundary where one oceanic plate descends beneath another typically produces which feature?

  1. A deep ocean trench with an associated volcanic arc Correct answer.
  2. A passive continental margin
  3. A broad rift valley with normal faulting
  4. A linear chain of hot-spot shield volcanoes

Explanation

Subduction of dense oceanic lithosphere creates a trench and releases water that promotes melting in the overlying mantle wedge. The magma rises to form a volcanic arc, often with associated earthquakes. This pairing of trench and arc is characteristic of subduction zones.

Question 6Earth systems and the geosphere

Which type of plate boundary is associated with shallow-focus earthquakes along a narrow fault zone where lithosphere is neither created nor destroyed?

  1. A transform boundary Correct answer.
  2. A continental collision zone
  3. A subduction zone
  4. A divergent boundary

Explanation

Transform boundaries accommodate horizontal sliding between plates, producing shallow earthquakes along a narrow fault trace. Crust is conserved because material is neither added nor removed. The San Andreas Fault is a well-known example.

Question 7Earth systems and the geosphere

The elastic rebound theory explains the origin of earthquakes as resulting from which process?

  1. Rapid cooling and contraction of magma underground
  2. Expansion of rock caused by tidal heating
  3. Sudden release of accumulated strain along a fault Correct answer.
  4. Collapse of a cave roof under its own weight

Explanation

Rocks on either side of a fault bend elastically as stress builds, storing strain energy. When friction is overcome, the rocks rupture and snap back to a less strained shape, releasing energy as seismic waves. This sudden rebound generates the earthquake.

Question 8Earth systems and the geosphere

Which seismic wave type travels through both solids and liquids and arrives first at a recording station?

  1. Rayleigh waves
  2. Secondary (S) waves
  3. Primary (P) waves Correct answer.
  4. Love waves

Explanation

P waves are compressional waves and are the fastest seismic waves, so they arrive first. Because they involve volume change, they can propagate through solids, liquids and gases. Their ability to pass through the outer core is key evidence that it is liquid.

Question 9Earth systems and the geosphere

A seismograph station records a 40-second interval between the first P wave and the first S wave. Which conclusion is most defensible?

  1. The earthquake had a magnitude greater than 7
  2. The earthquake occurred directly beneath the station
  3. The earthquake generated a tsunami
  4. The earthquake epicentre is at a determinable distance from the station Correct answer.

Explanation

The S minus P time interval increases systematically with distance because the two wave types travel at different speeds. A single station therefore yields the distance to the epicentre. Three stations are needed to locate the epicentre by triangulation.

Question 10Earth systems and the geosphere

Which magma composition is generally the most viscous and therefore associated with explosive eruptions?

  1. High-silica, low-temperature magma Correct answer.
  2. High-iron, low-silica magma
  3. Low-silica, low-gas magma
  4. Low-silica, high-temperature magma

Explanation

Silica-rich magma polymerises into long chains, raising viscosity, and it also tends to be cooler, which further increases viscosity. High viscosity traps gas until pressure builds and is released explosively. Basaltic magma, by contrast, is hot and fluid.

Question 11Earth systems and the geosphere

Which process contributes most directly to the formation of soil from solid bedrock?

  1. Metamorphism of the parent rock
  2. Melting of the parent rock
  3. Physical and chemical weathering of the parent rock Correct answer.
  4. Deposition of sediment in a river delta

Explanation

Soil develops as bedrock is broken down physically and altered chemically, producing loose mineral particles. These particles are then mixed with organic matter and reorganised by biological activity. Weathering is therefore the essential first step in soil formation.

Question 12Earth systems and the geosphere

In a soil profile, which horizon is typically richest in accumulated organic matter?

  1. The R horizon
  2. The C horizon
  3. The O horizon Correct answer.
  4. The B horizon

Explanation

The O horizon is the surface layer dominated by partly decomposed plant litter and humus. Organic matter is most concentrated there because fresh litter is added from above. Lower horizons contain progressively less organic material.

Question 13Earth systems and the geosphere

Which soil property is most directly increased by the addition of well-decomposed organic matter?

  1. Particle size of the sand fraction
  2. Bulk density
  3. Water-holding capacity Correct answer.
  4. Depth to bedrock

Explanation

Organic matter creates pore space and binds soil particles into aggregates, both of which increase the soil's ability to retain water. It also lowers bulk density and improves structure. It does not change the size of mineral grains or bedrock depth.

Question 14Earth systems and the geosphere

Which combination of factors most strongly promotes rapid chemical weathering of bedrock?

  1. Cold temperature, abundant rainfall and low surface area
  2. Warm temperature, abundant rainfall and high surface area Correct answer.
  3. Warm temperature, low rainfall and coarse unbroken rock
  4. Cold temperature, low rainfall and massive joint-free rock

Explanation

Chemical reactions proceed faster at higher temperatures and require water as a reactant and transport medium. Greater surface area exposes more mineral surfaces to attack. Together these conditions accelerate hydrolysis and oxidation.

Question 15Earth systems and the geosphere

Which sedimentary rock type forms primarily from the precipitation of dissolved ions from water?

  1. Intrusive igneous rock such as granite
  2. Chemical sedimentary rock such as limestone Correct answer.
  3. Clastic sedimentary rock such as sandstone
  4. Foliated metamorphic rock such as schist

Explanation

Chemical sedimentary rocks form when dissolved substances precipitate, either through evaporation or biological and chemical processes. Limestone, for example, accumulates from calcium carbonate. Clastic rocks instead form from transported fragments.

Question 16Earth systems and the geosphere

A rock is deeply buried and subjected to high temperature and pressure without melting, developing a new foliated texture. Which rock type has formed?

  1. Metamorphic rock Correct answer.
  2. Volcanic glass
  3. Clastic sedimentary rock
  4. Igneous rock

Explanation

Metamorphism recrystallises minerals in the solid state under changed temperature and pressure conditions. Directed pressure aligns platy minerals, producing foliation. Melting would instead generate magma and eventually igneous rock.

Question 17Earth systems and the geosphere

Which statement best describes the role of the rock cycle in recycling Earth materials?

  1. Rocks are recycled only when they are completely melted
  2. Sedimentary rocks are permanent and cannot change
  3. Any rock type can be transformed into another through geological processes Correct answer.
  4. Only igneous rocks can be converted into sedimentary rocks

Explanation

The rock cycle links melting, weathering, erosion, deposition, burial and metamorphism, allowing material to pass between all three rock classes. The pathways are not fixed, and any rock can be transformed given the right conditions. This makes the cycle a continuous recycling system.

Question 18Earth systems and the geosphere

The asthenosphere is best described as which of the following?

  1. A weak, partially molten zone of the upper mantle that allows plate movement Correct answer.
  2. The outermost layer of the atmosphere
  3. The liquid metallic layer surrounding the inner core
  4. A rigid layer comprising the crust and uppermost mantle

Explanation

The asthenosphere lies beneath the lithosphere and deforms plastically over long timescales, partly because it is near its melting point. This weak layer permits the overlying rigid plates to move. It is not fully molten, so seismic shear waves still pass through it.

Question 19Earth systems and the geosphere

Which mechanism is the main driver of lithospheric plate motion?

  1. Magnetic attraction between plates
  2. Slab pull from the sinking of dense subducting plates Correct answer.
  3. Centrifugal force from Earth's rotation
  4. Tidal forces from the Moon

Explanation

Cold, dense oceanic lithosphere sinking at subduction zones exerts a strong pulling force on the trailing plate. This slab pull is generally considered the dominant driving force, supplemented by ridge push and mantle convection. Tidal and rotational forces are far too weak to move plates.

Question 20Earth systems and the geosphere

Paleomagnetic stripes of alternating normal and reversed polarity on the seafloor are symmetric about mid-ocean ridges. This pattern is best explained by which process?

  1. Selective magnetisation caused by ocean currents
  2. Random magnetisation of sediment deposited on the ocean floor
  3. New crust recording field reversals as it forms and spreads away from the ridge Correct answer.
  4. Repeated reversals of the ridge's position over time

Explanation

As magma cools at the ridge, magnetic minerals align with the prevailing field direction and lock in that record. Continued spreading carries the magnetised crust symmetrically away from the ridge on both sides. The resulting mirror-image stripes document field reversals and confirm seafloor spreading.

Question 21Earth systems and the geosphere

Which feature forms where two continental plates collide?

  1. A mid-ocean ridge
  2. A deep ocean trench without volcanism
  3. A transform fault with lateral sliding
  4. A broad, thickened mountain belt Correct answer.

Explanation

Continental lithosphere is relatively buoyant, so neither plate readily subducts during collision. The crust instead shortens and thickens, uplifting extensive mountain belts such as the Himalayas. This contrasts with oceanic subduction, which produces trenches and arcs.

Question 22Earth systems and the geosphere

Which factor most increases the potential for a slope to fail?

  1. Increased pore water pressure within the slope material Correct answer.
  2. Reduction of slope angle
  3. Increased cohesion between slope particles
  4. Removal of vegetation from the slope

Explanation

Water filling pore spaces reduces effective normal stress and can act as a lubricant, lowering the shear strength of the material. This raises the shear stress relative to strength and promotes failure. Heavy rainfall is therefore a common trigger of landslides.

Question 23Earth systems and the geosphere

Which process transports weathered material downslope under the direct influence of gravity, without a flowing transporting medium such as water or wind?

  1. Fluvial transport
  2. Glacial transport
  3. Mass wasting Correct answer.
  4. Aeolian transport

Explanation

Mass wasting is the downslope movement of rock and soil driven primarily by gravity acting on the material itself. It does not require a moving fluid to carry the load. Water may trigger it by reducing strength, but it is not the transporting medium.

Question 24Earth systems and the geosphere

Which statement about the formation of oil and natural gas is most accurate?

  1. They accumulate only in igneous intrusive bodies
  2. They form from the cooling of iron-rich magma
  3. They are produced by weathering of granite at the surface
  4. They form from buried organic matter heated within a limited depth and temperature range Correct answer.

Explanation

Organic-rich sediment buried to suitable depths is heated into a temperature range often called the oil window. Too shallow and the organic matter remains immature; too deep and it is converted largely to gas or destroyed. Migration and trapping then concentrate the hydrocarbons.

Question 25Earth systems and the geosphere

Which observation best supports the interpretation that a region's climate was once much wetter than today?

  1. Steeply dipping sedimentary layers
  2. A high proportion of quartz in local granite
  3. Relict river channels and lake beds preserved in a now-arid landscape Correct answer.
  4. Fresh lava flows on the surface

Explanation

Preserved channels and lake beds indicate that flowing and standing water were once abundant. Such features cannot form in the current dry conditions, so they record a wetter past. This is a standard line of evidence for past climate change.

Question 26Earth systems and the geosphere

Which layer of Earth's interior is composed mainly of solid iron and nickel and lies beneath the liquid outer core?

  1. The inner core Correct answer.
  2. The asthenosphere
  3. The lower mantle
  4. The continental crust

Explanation

Earth's core is divided into a liquid outer core and a solid inner core. The inner core is solid because pressures there are extreme, even though temperatures are very high, and it consists mainly of iron with some nickel.

Question 27Earth systems and the geosphere

A geologist finds a mineral that can be scratched by a copper coin but not by a fingernail. Which property is being tested?

  1. Cleavage
  2. Hardness Correct answer.
  3. Streak
  4. Luster

Explanation

Hardness is a mineral's resistance to being scratched, ranked on the Mohs scale. Comparing whether a fingernail or a copper coin can scratch a specimen places the mineral between those two reference hardness values.

Question 28Earth systems and the geosphere

Which type of volcano is characterised by broad, gently sloping flanks built from low-viscosity basaltic lava flows?

  1. Shield volcano Correct answer.
  2. Stratovolcano
  3. Caldera
  4. Cinder cone

Explanation

Shield volcanoes form when fluid basaltic lava travels long distances before cooling, producing wide, gently inclined profiles. Their low-viscosity magma allows gases to escape readily, so eruptions are usually effusive rather than violently explosive.

Question 29Earth systems and the geosphere

Which evidence first led Alfred Wegener to propose that continents have moved over Earth's surface?

  1. Matching fossil and rock sequences across widely separated continents Correct answer.
  2. Measurements of seafloor magnetic stripe patterns
  3. Satellite measurements of present-day plate velocities
  4. Deep-sea drilling records of sediment thickness

Explanation

Wegener assembled evidence such as matching fossils, rock types and ancient glacial deposits on continents now separated by oceans. These matches implied the landmasses were once joined and later drifted apart.

Question 30Earth systems and the geosphere

A sedimentary basin contains a thick sequence of limestone overlain by shale. What does the change from limestone to shale most likely indicate about the depositional environment?

  1. A change from a warm carbonate-rich sea to a muddy, lower-energy setting Correct answer.
  2. A period of intense metamorphism affecting the older beds
  3. A sudden increase in volcanic ash input to the basin
  4. A shift from quiet deep water to a high-energy shoreline

Explanation

Limestone typically forms in warm, shallow marine water where carbonate-secreting organisms thrive and fine sediment is scarce. Shale forms from fine mud deposited in quieter water, so the upward change records a shift in water clarity, sediment supply and energy.

Question 31Earth systems and the geosphere

Which process is the main way that clastic sediment becomes solid sedimentary rock?

  1. Melting followed by slow cooling
  2. Chemical precipitation from seawater alone
  3. Recrystallisation under directed stress
  4. Compaction and cementation of grains Correct answer.

Explanation

Lithification of clastic sediment involves squeezing out pore water through compaction and binding grains with minerals such as calcite or quartz cement. Together these processes convert loose sand, silt or gravel into solid rock.

Question 32Earth systems and the geosphere

A granite intrusion cuts across horizontal sandstone layers, and the sandstone is baked and hardened along the contact. Which statement about relative ages is best supported?

  1. The intrusion is younger than the sandstone Correct answer.
  2. The intrusion and sandstone formed at the same time
  3. The sandstone is younger than the intrusion
  4. The sandstone was deposited after the intrusion cooled

Explanation

A cross-cutting intrusion must be younger than the rocks it cuts through, following the principle of cross-cutting relationships. The baked contact zone shows the hot magma altered the existing sandstone, confirming the sandstone was already present.

Question 33Earth systems and the geosphere

A radioactive parent isotope has a half-life of 50 million years. Analysis shows that a mineral grain contains three times as many daughter atoms as parent atoms. Approximately how old is the grain?

  1. 50 million years
  2. 75 million years
  3. 100 million years Correct answer.
  4. 150 million years

Explanation

A daughter-to-parent ratio of 3:1 means that one quarter of the original parent remains, because parent plus daughter totals four parts. Remaining parent reaches one quarter after two half-lives, so the age is two multiplied by 50 million years.

Question 34Earth systems and the geosphere

Which type of unconformity is represented by an erosion surface where sedimentary layers rest directly on folded, metamorphosed rocks?

  1. Disconformity
  2. Paraconformity
  3. Angular unconformity
  4. Nonconformity Correct answer.

Explanation

A nonconformity is an erosion surface that separates sedimentary strata from older igneous or metamorphic rocks. The deeply buried and deformed basement was exposed by erosion before the younger sediments were deposited on top.

Question 35Earth systems and the geosphere

Which structural feature forms when rock layers are compressed and bend upward into an arch, with the oldest beds exposed in the centre?

  1. Strike-slip fault
  2. Anticline Correct answer.
  3. Syncline
  4. Normal fault

Explanation

An anticline is an upward fold produced by compressional forces, with limbs dipping away from the crest. Because folding arches the layers, the oldest rocks are exposed along the eroded core of the fold.

Question 36Earth systems and the geosphere

An ore deposit containing copper sulfide minerals is found in a zone where hydrothermal fluids circulated through fractured volcanic rock. Which process most likely concentrated the metals?

  1. Metamorphic recrystallisation of the surrounding shale
  2. Weathering of the host rock at the surface
  3. Sorting of mineral grains by river currents
  4. Precipitation from hot fluids as they cooled and reacted with wall rock Correct answer.

Explanation

Hydrothermal ore deposits form when hot, metal-bearing fluids move through fractures and then cool or react with the host rock. These changes reduce metal solubility, causing sulfide minerals to precipitate in veins and replacement zones.

Question 37Earth systems and the geosphere

Which combination of conditions most favours the preservation of abundant plant material as coal?

  1. Repeated heating above 200 degrees Celsius
  2. Rapid burial in a waterlogged, oxygen-poor setting Correct answer.
  3. Deposition in fast-flowing, oxygen-rich water
  4. Slow burial in a dry, well-aerated setting

Explanation

Coal forms from accumulated plant remains that are protected from complete decay. Waterlogged, oxygen-poor conditions limit microbial oxidation, and rapid burial keeps the organic matter within the sediment.

Question 38Earth systems and the geosphere

A groundwater aquifer is confined between two impermeable clay layers. Which statement about this aquifer is most accurate?

  1. It is recharged only by direct rainfall through the surface
  2. It cannot store or transmit water because it is confined
  3. Its water is under pressure, so a well may flow without pumping Correct answer.
  4. Its water table is always exposed to the atmosphere

Explanation

A confined aquifer is bounded by impermeable layers and its water is under confining pressure. When a well penetrates the aquifer, water may rise above the aquifer top and even flow at the surface as an artesian well.

Question 39Earth systems and the geosphere

A sequence of marine sedimentary rocks contains a bed with abundant shallow-water coral fossils overlain by deep-water pelagic mudstone. Which interpretation is best supported?

  1. The area underwent regional metamorphism
  2. Sea level fell and the seafloor was exposed
  3. The coral bed was deposited after the mudstone
  4. Sea level rose relative to the land at this location Correct answer.

Explanation

Coral indicates warm, shallow, well-lit water, while pelagic mudstone accumulates in deeper, quieter water. The upward change from shallow to deep facies records a relative rise in sea level, known as transgression.

Question 40Earth systems and the geosphere

A large igneous province was emplaced rapidly at about 250 million years ago, coinciding with a mass extinction. Which mechanism best links the eruption to the extinction?

  1. Formation of new continental crust along a subduction zone
  2. Increased release of carbon dioxide and sulfur gases altering climate and ocean chemistry Correct answer.
  3. Rapid cooling of the mantle beneath the province
  4. A decrease in cosmic radiation reaching Earth's surface

Explanation

Flood basalt eruptions release large volumes of carbon dioxide and sulfur dioxide, which can drive warming, acidification and short-term cooling. These environmental stresses, together with associated effects, can destabilise ecosystems and contribute to mass extinction.

Question 41Earth materials, rocks and minerals

Which mineral property is defined as the colour of a mineral's powder when it is rubbed across an unglazed porcelain plate?

  1. Streak Correct answer.
  2. Cleavage
  3. Hardness
  4. Lustre

Explanation

Streak is the colour of the fine powder left when a mineral is scraped on unglazed porcelain, and it is often more reliable than the whole-crystal colour because it is less affected by surface weathering or impurities. Lustre, cleavage and hardness describe surface reflection, breaking patterns and scratch resistance respectively, so none of them refers to powder colour.

Question 42Earth materials, rocks and minerals

A mineral can be scratched by a copper coin but not by a fingernail. Using Mohs scale, which hardness range is most consistent with this observation?

  1. About 1 to 2
  2. About 2.5 to 3.5 Correct answer.
  3. About 6 to 7
  4. About 8 to 9

Explanation

A fingernail has a Mohs hardness of about 2.5 and a copper coin about 3 to 3.5, so a mineral scratched by the coin but not the nail must lie between these values. Hardness values near 6 to 7 correspond to materials such as feldspar or quartz, which a copper coin cannot scratch.

Question 43Earth materials, rocks and minerals

Which type of bonding within silicate minerals gives rise to perfect cleavage in one direction, as seen in micas?

  1. Weak sheets of silicate tetrahedra held by weak bonds between layers Correct answer.
  2. Isolated tetrahedra joined only by ionic bonds to metal cations
  3. Chains of tetrahedra cross-linked by strong covalent bonds
  4. A three-dimensional framework of tetrahedra sharing all four oxygens

Explanation

Mica structures consist of strong sheets of linked silicate tetrahedra stacked and held together by comparatively weak bonds, so the crystal splits readily between sheets to give perfect basal cleavage. Framework, isolated and chain structures lack these weak planar boundaries and therefore break differently.

Question 44Earth materials, rocks and minerals

Which statement best explains why quartz has a conchoidal fracture rather than cleavage?

  1. Its framework of tetrahedra has no planes of weak bonding Correct answer.
  2. It contains no silicon-oxygen bonds
  3. It is softer than most other minerals
  4. Its atoms are arranged in random disorder

Explanation

In quartz every oxygen in the silicate framework is shared between tetrahedra, producing a strong three-dimensional network with no preferred plane of weakness. When it breaks, it therefore produces curved, glass-like conchoidal surfaces instead of flat cleavage planes.

Question 45Earth materials, rocks and minerals

Which of the following minerals is a common dark-coloured ferromagnesian silicate found in mafic rocks such as basalt?

  1. Olivine Correct answer.
  2. Quartz
  3. Calcite
  4. Muscovite

Explanation

Olivine is a magnesium-iron silicate that is dark green and common in mafic and ultramafic rocks such as basalt and peridotite. Quartz and muscovite are light-coloured felsic minerals, and calcite is a carbonate rather than a ferromagnesian silicate.

Question 46Earth materials, rocks and minerals

An igneous rock has large crystals surrounded by a much finer groundmass. Which interpretation of this texture is most reasonable?

  1. Slow crystallisation at depth followed by rapid cooling near the surface Correct answer.
  2. Formation entirely by metamorphic recrystallisation
  3. Complete melting and quenching of a magma in one single event
  4. Rapid cooling at the surface followed by slow reheating at depth

Explanation

A porphyritic texture records two cooling stages: large phenocrysts grew slowly within a magma chamber at depth, then the remaining melt rose and cooled quickly to form the fine groundmass. This two-stage history produces the contrast in crystal size.

Question 47Earth materials, rocks and minerals

Which magma composition is most viscous, and therefore most likely to produce explosive eruptions?

  1. High-silica, low-temperature rhyolitic magma Correct answer.
  2. Low-silica, low-gas komatiitic magma
  3. Low-silica, high-temperature basaltic magma
  4. High-magnesium, high-temperature picritic magma

Explanation

Viscosity rises with silica content and falls with temperature, so cool, silica-rich rhyolitic magma is the most viscous and traps gas until pressure builds up and is released explosively. Hot, low-silica magmas such as basalt are fluid and allow gas to escape more gently.

Question 48Earth materials, rocks and minerals

Which feature is characteristic of intrusive igneous rocks compared with extrusive rocks?

  1. Coarse-grained texture from slow cooling at depth Correct answer.
  2. A glassy texture from rapid quenching
  3. Vesicles formed by escaping gas
  4. Abundant volcanic ash layers

Explanation

Intrusive rocks solidify deep underground where heat loss is slow, allowing large crystals to grow and producing a coarse-grained texture. Extrusive rocks cool quickly at the surface, giving fine grains, vesicles or glass.

Question 49Earth materials, rocks and minerals

Which sedimentary rock is most likely to form from the accumulation and compaction of sand-sized quartz grains?

  1. Shale
  2. Rock salt
  3. Limestone
  4. Sandstone Correct answer.

Explanation

Sandstone is a clastic sedimentary rock composed mainly of sand-sized grains, commonly quartz, cemented after compaction. Limestone is mainly calcium carbonate, shale is made of clay-sized particles, and rock salt forms by evaporation of saline water.

Question 50Earth materials, rocks and minerals

A sedimentary rock contains grains that are well rounded and well sorted. What does this suggest about its transport history?

  1. Very short transport from the source with little abrasion
  2. Chemical precipitation from evaporating seawater
  3. Long transport by water or wind, allowing abrasion and grain-size sorting Correct answer.
  4. Deposition directly from glacial ice without sorting

Explanation

Rounding develops as grains collide and abrade during transport, and good sorting arises where a transporting agent carries particles of similar size over long distances. Water and wind both produce such mature textures, whereas ice or direct chemical precipitation does not.