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NCEA Level 3 Earth and Space Science study materials
NCEA Level 3 Earth and Space Science study resources

NCEA Level 3 Earth and Space Science practice questions

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Question 1Earth and Space Science (Level 3 achievement standards)

In the rock cycle, which process converts loose sediment into solid sedimentary rock?

  1. Rapid cooling of a melt
  2. Compaction and cementation of grains Correct answer.
  3. Partial melting of the sediment
  4. Foliation under directed pressure

Explanation

Sedimentary rock forms when loose grains are buried, squeezed together (compaction) and bound by precipitated minerals (cementation). Melting and cooling produce igneous rocks, while foliation is a metamorphic process, so only lithification turns sediment into sedimentary rock.

Question 2Earth and Space Science (Level 3 achievement standards)

A divergent plate boundary where new oceanic lithosphere is created is best described as:

  1. A subduction zone marked by deep earthquakes
  2. A transform fault with strike-slip motion
  3. A continental collision belt with thrust faulting
  4. A mid-ocean ridge with shallow earthquakes and basaltic volcanism Correct answer.

Explanation

At mid-ocean ridges, mantle upwelling and decompression melting generate basaltic magma that builds new oceanic crust, producing shallow-focus earthquakes and volcanic activity along the ridge axis. Subduction, transform and collision settings involve convergence or lateral sliding rather than crustal creation.

Question 3Earth and Space Science (Level 3 achievement standards)

Which statement correctly describes the relationship between the focus and epicentre of an earthquake?

  1. The focus is the point of rupture on the fault and the epicentre is the point on the surface directly above it Correct answer.
  2. The epicentre is the point of rupture on the fault and the focus is directly above it
  3. The focus lies on the surface and the epicentre lies at depth within the crust
  4. The epicentre and focus are both located at the same depth within the fault plane

Explanation

The focus (hypocentre) is the actual location where rupture begins on the fault plane, at some depth in the crust. The epicentre is the point on the Earth's surface vertically above the focus, which is why it is used to locate earthquakes on maps.

Question 4Earth and Space Science (Level 3 achievement standards)

The greenhouse effect that keeps Earth's surface warmer than its blackbody temperature depends primarily on:

  1. Release of latent heat during condensation of water vapour
  2. Reflection of sunlight by clouds and ice
  3. Absorption and re-emission of longwave infrared radiation by atmospheric gases Correct answer.
  4. Conduction of heat from the mantle into the atmosphere

Explanation

Greenhouse gases such as water vapour and carbon dioxide absorb outgoing longwave infrared radiation and re-emit it in all directions, including back towards the surface. This traps energy and raises surface temperature above the value expected from solar input alone.

Question 5Earth and Space Science (Level 3 achievement standards)

Which observation provided key early evidence supporting the theory of plate tectonics?

  1. Uniform thickness of oceanic crust across all ocean basins
  2. Matching fossil and rock sequences on continents now separated by oceans Correct answer.
  3. Absence of earthquakes along island arcs
  4. Constant age of seafloor regardless of distance from ridges

Explanation

Wegener and later workers noted matching fossils, rock types and glacial deposits on now-separated continents, indicating they were once joined. Seafloor-age patterns and earthquake belts later reinforced the theory, so the other options contradict observed data.

Question 6Earth and Space Science (Level 3 achievement standards)

The main reason the Moon shows phases when viewed from Earth is that:

  1. The Moon's orbit is highly elliptical, changing its distance markedly
  2. Earth's shadow falls on different parts of the Moon each night
  3. The Moon changes its own luminosity cyclically
  4. We see varying fractions of the Moon's sunlit hemisphere as it orbits Earth Correct answer.

Explanation

Half the Moon is always sunlit, but as the Moon orbits Earth we view that sunlit half from changing angles, so the visible illuminated fraction changes through the cycle. The phases are not caused by Earth's shadow, which produces lunar eclipses instead.

Question 7Earth and Space Science (Level 3 achievement standards)

A mineral that breaks along smooth, flat planes reflecting its internal atomic structure is said to have:

  1. Conchoidal fracture
  2. Cleavage Correct answer.
  3. Magnetic susceptibility
  4. Vitreous lustre

Explanation

Cleavage is the tendency of a mineral to break along planes of weaker atomic bonding, producing smooth flat surfaces that reflect its internal structure. Fracture describes irregular breakage, while lustre and magnetism are unrelated physical properties.

Question 8Earth and Space Science (Level 3 achievement standards)

Which gas is the most abundant component of Earth's current atmosphere?

  1. Argon
  2. Nitrogen Correct answer.
  3. Carbon dioxide
  4. Oxygen

Explanation

Nitrogen makes up roughly 78 percent of the dry atmosphere by volume, making it the dominant gas. Oxygen is about 21 percent, while carbon dioxide and argon are present only in trace amounts.

Question 9Earth and Space Science (Level 3 achievement standards)

A geologist finds a sequence of undisturbed sedimentary layers in which a fossil species appears in a lower layer and a different species appears in an upper layer. What can be concluded?

  1. The upper species is older because it lies closer to the surface
  2. Both species lived at exactly the same time
  3. The lower species existed before the upper species Correct answer.
  4. The sequence has been overturned by folding

Explanation

The principle of superposition states that in an undisturbed sequence, lower layers were deposited first and are therefore older. Fossils in the lower layer thus represent an earlier interval of time than those above, allowing relative ages to be assigned.

Question 10Earth and Space Science (Level 3 achievement standards)

An igneous rock contains large crystals of quartz, feldspar and mica set in a fine-grained matrix. This texture most likely indicates that the magma:

  1. Cooled slowly at depth and then rapidly near the surface Correct answer.
  2. Was erupted underwater and quenched instantly
  3. Cooled extremely rapidly at the surface in one event
  4. Was metamorphosed after solidification

Explanation

Large crystals require slow cooling at depth, allowing ions time to organise into coarse grains. A fine-grained matrix indicates a later phase of rapid cooling, consistent with magma that partly crystallised in a chamber and then rose and cooled quickly nearer the surface.

Question 11Earth and Space Science (Level 3 achievement standards)

Oceanic lithosphere is subducted beneath continental lithosphere because oceanic lithosphere:

  1. Has a higher geothermal gradient
  2. Contains more continental crust
  3. Is denser and therefore sinks more readily Correct answer.
  4. Is thicker and therefore heavier

Explanation

Oceanic lithosphere is composed of dense mafic rock and, once cooled and thickened with age, becomes denser than the underlying asthenosphere, allowing it to sink at convergent boundaries. Continental lithosphere is thicker and more buoyant, so it resists subduction.

Question 12Earth and Space Science (Level 3 achievement standards)

A seismograph station records P-waves at 10:00:00 and S-waves at 10:00:40. The S-wave arrival is delayed relative to the P-wave because S-waves:

  1. Are reflected at the surface
  2. Travel more slowly through the same rock Correct answer.
  3. Travel faster but start later
  4. Cannot pass through the crust

Explanation

P-waves are compressional and travel faster than S-waves, which are shear waves, through the same material. The increasing time gap between the two arrivals therefore indicates a greater distance from the source, which is used to locate the epicentre.

Question 13Earth and Space Science (Level 3 achievement standards)

A student compares two locations at the same latitude: one on a west coast and one on an east coast adjacent to a warm ocean current. Which factor best explains a warmer mean annual temperature at the east-coast location?

  1. Advection of heat by the warm ocean current and prevailing winds Correct answer.
  2. Lower atmospheric pressure
  3. Higher elevation above sea level
  4. Greater distance from the equator

Explanation

Warm ocean currents transport heat poleward, and prevailing winds blowing onshore can advect that warmth over adjacent land, raising mean annual temperatures. Latitude, elevation and pressure alone do not explain the coastal contrast described.

Question 14Earth and Space Science (Level 3 achievement standards)

The Coriolis effect causes moving air masses in the Southern Hemisphere to be deflected:

  1. Directly towards the poles
  2. To the right of their direction of motion
  3. To the left of their direction of motion Correct answer.
  4. Directly towards the equator

Explanation

Because of Earth's rotation, freely moving objects appear deflected relative to the surface, to the left in the Southern Hemisphere and to the right in the Northern Hemisphere. This deflection shapes global wind belts and rotating weather systems.

Question 15Earth and Space Science (Level 3 achievement standards)

A star's spectrum shows its absorption lines shifted towards longer wavelengths compared with laboratory values. What does this indicate?

  1. The star is cooler than expected
  2. The star is moving away from the observer Correct answer.
  3. The star is rotating edge-on
  4. The star is moving towards the observer

Explanation

A redshift means the observed wavelengths are longer than emitted wavelengths, which occurs when the source is receding due to the Doppler effect. Blueshift would indicate approach, and temperature or rotation produce line broadening rather than a uniform shift.

Question 16Earth and Space Science (Level 3 achievement standards)

A sedimentary rock containing rounded pebbles cemented together most likely formed in an environment where:

  1. Limestone was metamorphosed by heat
  2. Magma cooled slowly underground
  3. Pebbles were transported by water or wind before burial Correct answer.
  4. Minerals precipitated from evaporating brine

Explanation

Rounded clasts indicate abrasion during transport by water or wind, and the cemented matrix indicates later lithification. Slow magma cooling, metamorphism and evaporation produce different textures and compositions.

Question 17Earth and Space Science (Level 3 achievement standards)

Why does the Hawaiian island chain show progressively older volcanic islands to the northwest?

  1. The islands are eroded more rapidly in the southeast
  2. The hotspot migrates southeast beneath a fixed plate
  3. The Pacific Plate moves northwest over a stationary mantle hotspot Correct answer.
  4. Sea level falls progressively to the northwest

Explanation

A mantle plume (hotspot) remains roughly fixed while the Pacific Plate moves over it, so volcanism builds new islands above the plume and older islands are carried away to the northwest. Their increasing age and erosion with distance support this model.

Question 18Earth and Space Science (Level 3 achievement standards)

Ice cores from Antarctica provide evidence about past climate mainly because they contain:

  1. Magnetic minerals that record plate motion
  2. Trapped air bubbles that preserve past atmospheric composition Correct answer.
  3. Fossils of marine organisms that record ocean depth
  4. Sedimentary layers that record river discharge

Explanation

Snow accumulates and traps air, which is sealed as bubbles in glacial ice, preserving samples of past atmospheric gases such as carbon dioxide and methane. Isotopic composition of the ice also records temperature, giving a detailed climate archive.

Question 19Earth and Space Science (Level 3 achievement standards)

Which statement best explains why the sky appears blue during the day?

  1. Ozone emits blue light when struck by sunlight
  2. Air molecules scatter short blue wavelengths more strongly than long red wavelengths Correct answer.
  3. The atmosphere absorbs all red light and emits blue light
  4. Clouds reflect blue light back to the surface

Explanation

Rayleigh scattering by air molecules is strongly wavelength-dependent, so shorter blue wavelengths are scattered far more than longer red ones, filling the sky with scattered blue light. At sunset the long path length removes much of the blue, leaving reds and oranges.

Question 20Earth and Space Science (Level 3 achievement standards)

A rock sample contains a radioactive parent isotope with a half-life of 100 million years, and 75 percent of the parent has decayed to daughter product. Assuming no loss of parent or daughter, the age of the sample is:

  1. 100 million years
  2. 200 million years Correct answer.
  3. 50 million years
  4. 400 million years

Explanation

After one half-life 50 percent of the parent remains; after two half-lives 25 percent remains, meaning 75 percent has decayed. Two half-lives of 100 million years give an age of 200 million years.

Question 21Earth and Space Science (Level 3 achievement standards)

An earthquake occurs beneath the ocean floor and displaces a large volume of water. Which sequence correctly describes the resulting tsunami as it crosses the deep ocean and approaches the coast?

  1. Short wavelength and low speed in deep water; shoaling increases speed and reduces wave height
  2. Long wavelength and high speed in deep water; shoaling increases speed and reduces height
  3. Constant wavelength and speed throughout; height depends only on wind strength
  4. Long wavelength and high speed in deep water; shoaling reduces speed and increases wave height Correct answer.

Explanation

Tsunami waves have very long wavelengths and travel fast across deep water with small amplitude. As they enter shallow coastal water, shoaling slows them and conserves energy by increasing wave height, producing destructive run-up.

Question 22Earth and Space Science (Level 3 achievement standards)

A region has a high mean annual rainfall but very low stream discharge and high evapotranspiration. The most likely explanation is that the region:

  1. Has highly permeable bedrock and dense vegetation, so water infiltrates and transpires Correct answer.
  2. Receives most rainfall as snow that melts rapidly
  3. Has extensive impermeable clay and sparse vegetation
  4. Has a steep gradient that increases runoff

Explanation

High infiltration into permeable rock reduces surface runoff, and dense vegetation returns much water to the atmosphere through transpiration. Together these processes lower stream discharge despite high rainfall.

Question 23Earth and Space Science (Level 3 achievement standards)

Two stars have the same luminosity, but star A has twice the surface temperature of star B. Using the Stefan-Boltzmann relation, the radius of star A compared with star B is:

  1. Four times
  2. Twice
  3. One quarter
  4. One half Correct answer.

Explanation

Luminosity scales as radius squared times temperature to the fourth power. With equal luminosity, doubling the temperature requires the radius to fall by a factor of four under the fourth-power term, giving a radius half that of star B.

Question 24Earth and Space Science (Level 3 achievement standards)

A mid-latitude weather system intensifies when a surface low-pressure centre is located beneath a region of upper-level divergence. Why does this occur?

  1. Divergence aloft adds mass, raising surface pressure and suppressing uplift
  2. Divergence aloft removes mass, lowering surface pressure and strengthening convergence and uplift Correct answer.
  3. Upper-level divergence has no effect on surface pressure
  4. Upper-level divergence cools the surface air and increases its density

Explanation

When air diverges aloft faster than it converges at the surface, mass is removed from the column, so surface pressure falls and low-level convergence and ascent strengthen. This coupling between upper and lower levels drives cyclogenesis.

Question 25Earth and Space Science (Level 3 achievement standards)

A metamorphic rock is found to contain the mineral assemblage kyanite plus garnet, indicating high pressure and moderate temperature. Which tectonic setting is most consistent with this condition?

  1. A shallow contact aureole around a magma intrusion
  2. A mid-ocean ridge where hot mantle rises
  3. A deep continental collision zone where crust is thickened Correct answer.
  4. A near-surface evaporite basin

Explanation

Kyanite and garnet together record high-pressure, moderate-temperature metamorphism typical of thickened crust in continental collision zones. Contact metamorphism, ridge settings and evaporite basins do not produce such high-pressure assemblages.

Question 26Earth and Space Science (Level 3 achievement standards)

Which layer of Earth's interior is inferred to be liquid because S-waves cannot pass through it?

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

Explanation

S-waves are shear waves and cannot travel through liquids, so their absence beyond about 103 degrees from an earthquake epicentre reveals a liquid layer. This S-wave shadow zone is explained by the liquid outer core, which lies between the solid inner core and the mantle.

Question 27Earth and Space Science (Level 3 achievement standards)

Which process is the main way energy is transferred through the mantle over geological time?

  1. Convection of slowly flowing solid rock Correct answer.
  2. Friction along transform faults
  3. Conduction through stationary crystal lattices
  4. Radiation through magma chambers

Explanation

Although mantle rock is solid, at high temperature and pressure it deforms slowly over millions of years, allowing convection currents to carry heat. This convection drives plate motion and is distinct from conduction, which is far too slow to move heat through such a thick layer.

Question 28Earth and Space Science (Level 3 achievement standards)

A transform plate boundary is best described as a location where two plates:

  1. Slide horizontally past one another without significant crust being created or destroyed Correct answer.
  2. Remain stationary while a hot spot moves beneath them
  3. Collide, with one plate descending beneath the other
  4. Move directly apart, with new oceanic crust forming between them

Explanation

At a transform boundary, plates move laterally past each other and crust is neither created nor destroyed, producing shallow-focus earthquakes along the fault. The San Andreas Fault is a well-known continental example of this boundary type.

Question 29Earth and Space Science (Level 3 achievement standards)

Which natural process currently removes the largest amount of carbon dioxide from the atmosphere on an annual basis?

  1. Photosynthesis by marine and terrestrial plants Correct answer.
  2. Volcanic outgassing
  3. Weathering of limestone by carbonic acid
  4. Combustion of fossil fuels

Explanation

Photosynthesis by ocean phytoplankton and land plants fixes atmospheric carbon dioxide into organic matter each year, forming the largest annual biological carbon sink. This uptake is partly offset by respiration and decay, but it dominates short-term removal.

Question 30Earth and Space Science (Level 3 achievement standards)

Which evidence best supports the theory that Earth's magnetic field has reversed many times in the past?

  1. Seasonal changes in the aurora borealis
  2. The presence of iron-rich minerals in continental granites
  3. The deflection of compass needles near the poles
  4. Symmetrical magnetic striping recorded in oceanic crust on either side of mid-ocean ridges Correct answer.

Explanation

As new oceanic crust forms at a ridge and cools, magnetic minerals record the field direction at that time, producing symmetrical stripes of normal and reversed polarity on both sides. This pattern, matched with radiometric ages, shows repeated reversals and supports seafloor spreading.

Question 31Earth and Space Science (Level 3 achievement standards)

Which factor most strongly determines whether a magma erupts explosively or flows quietly?

  1. The dissolved gas content and viscosity of the magma Correct answer.
  2. The age of the surrounding country rock
  3. The depth of the nearest ocean trench
  4. The latitude of the volcano

Explanation

Explosive eruptions occur when viscous, gas-rich magma traps volatiles until pressure builds and is released violently. Low-viscosity, gas-poor magma allows bubbles to escape easily, producing quiet lava flows.

Question 32Earth and Space Science (Level 3 achievement standards)

Which statement correctly describes the greenhouse effect?

  1. Clouds prevent all outgoing radiation from leaving the atmosphere
  2. Atmospheric gases reflect incoming ultraviolet radiation back into space
  3. Ozone absorbs visible light and converts it into heat at the surface
  4. Certain atmospheric gases absorb and re-emit outgoing infrared radiation, warming the lower atmosphere Correct answer.

Explanation

Greenhouse gases such as carbon dioxide, methane and water vapour absorb infrared radiation emitted by Earth's surface and re-radiate it, some of which returns to the surface and raises temperature. This process warms the lower atmosphere and is distinct from reflection of incoming sunlight.

Question 33Earth and Space Science (Level 3 achievement standards)

Which observation was a key piece of evidence supporting the Big Bang model?

  1. The retrograde motion of Mars against the background stars
  2. The presence of sunspots on the solar surface
  3. The cosmic microwave background radiation filling all of space Correct answer.
  4. The existence of impact craters on the Moon

Explanation

The cosmic microwave background is relic radiation from the early hot, dense universe, now cooled and redshifted into microwaves. Its uniform temperature across the sky strongly supports an expanding universe originating from a hot dense state.

Question 34Earth and Space Science (Level 3 achievement standards)

A geologist observes that a fault cuts through a sedimentary layer but does not displace the overlying lava flow. Which conclusion is best supported?

  1. The lava flow is older than the sedimentary layer
  2. The fault formed after the sedimentary layer but before the lava flow was erupted Correct answer.
  3. The sedimentary layer and lava flow were deposited at exactly the same time
  4. The fault formed after the lava flow was erupted

Explanation

The principle of cross-cutting relationships states that a feature which cuts another is younger than the material it cuts. Because the fault displaces the sediment but not the lava, the fault is younger than the sediment and older than the lava.

Question 35Earth and Space Science (Level 3 achievement standards)

A rock is composed mainly of the mineral calcite and fizzes when dilute hydrochloric acid is applied. Which rock type is it most likely to be?

  1. Quartzite
  2. Obsidian
  3. Basalt
  4. Limestone Correct answer.

Explanation

Calcite is calcium carbonate, which reacts with acid to release carbon dioxide, and it is the dominant mineral in limestone. The fizzing acid test is a standard field identification for carbonate rocks.

Question 36Earth and Space Science (Level 3 achievement standards)

An air mass moves from a warm ocean surface onto a cooler landmass. Which weather change is most likely to result?

  1. An increase in atmospheric pressure at the surface
  2. A rapid decrease in relative humidity
  3. Formation of low cloud and possibly fog as the air cools to its dew point Correct answer.
  4. Clear skies caused by descending warm air

Explanation

When warm, moist air moves over a cooler surface, it is cooled from below, raising relative humidity toward saturation and promoting condensation into low cloud or fog. This is the process of advection fog and stratiform cloud formation.

Question 37Earth and Space Science (Level 3 achievement standards)

A weather map shows tightly packed isobars around a low-pressure centre. What does this indicate about the winds there?

  1. Light winds because the pressure gradient is weak
  2. Strong winds because the pressure gradient is steep Correct answer.
  3. Winds blowing directly outward from the centre in all directions
  4. No wind because the pressure is uniform

Explanation

The spacing of isobars represents the pressure gradient; closely spaced isobars mean a large pressure change over a short distance. A steep pressure gradient produces stronger pressure-gradient force and therefore stronger winds.

Question 38Earth and Space Science (Level 3 achievement standards)

A star has a parallax angle of 0.05 arcseconds as measured from Earth. What is its approximate distance?

  1. 200 parsecs
  2. 5 parsecs
  3. 20 parsecs Correct answer.
  4. 0.05 parsecs

Explanation

Distance in parsecs equals one divided by the parallax angle in arcseconds, so 1 divided by 0.05 gives 20 parsecs. This relationship is the basis of the parallax distance method for nearby stars.

Question 39Earth and Space Science (Level 3 achievement standards)

A region experiences frequent shallow earthquakes and basaltic lava flows with little explosive activity. Which tectonic setting is most consistent with these observations?

  1. A subduction zone beneath a continent
  2. An intraplate region far from any boundary
  3. A divergent boundary such as a mid-ocean ridge Correct answer.
  4. A continental collision zone

Explanation

Divergent boundaries produce shallow-focus earthquakes from normal faulting and low-viscosity basaltic magma that flows quietly. The absence of explosive andesitic volcanism argues against subduction.

Question 40Earth and Space Science (Level 3 achievement standards)

A sediment core from the deep ocean shows a change from coarse-grained sediment to fine-grained clay above a certain depth. What is the most reasonable interpretation?

  1. The depositional energy decreased, allowing only finer particles to settle Correct answer.
  2. The sediment source suddenly became richer in coarse material
  3. The core was contaminated with larger grains
  4. The ocean current speed increased at that time

Explanation

Larger particles require higher energy to transport and settle, so a shift upward from coarse to fine sediment indicates declining current or wave energy at that location. This is an application of the principle that grain size reflects depositional energy.

Question 41Earth and Space Science (Level 3 achievement standards)

A planet orbits a star at a distance where liquid water can exist on its surface. This region is commonly described as:

  1. The Kuiper belt
  2. The habitable zone Correct answer.
  3. The asteroid belt
  4. The corona

Explanation

The habitable zone is the range of orbital distances from a star where a planet with a suitable atmosphere could maintain liquid water on its surface. It is a key criterion in the search for potentially life-bearing exoplanets.

Question 42Earth and Space Science (Level 3 achievement standards)

A student measures the angle of the noon Sun above the horizon at two locations on the same meridian and finds a difference of 7 degrees. What can be concluded?

  1. The two locations are separated by about 7 degrees of latitude Correct answer.
  2. The two locations are separated by about 7 degrees of longitude
  3. The Earth's rotation rate has changed
  4. The Sun's declination has changed by 7 degrees

Explanation

The altitude of the noon Sun depends on latitude, so a difference in solar altitude along the same meridian corresponds to a difference in latitude. Eratosthenes used this principle to estimate Earth's circumference.

Question 43Earth and Space Science (Level 3 achievement standards)

An igneous intrusion cuts across horizontal sedimentary layers and is itself cut by a younger fault. Which sequence of events is correct from oldest to youngest?

  1. Sedimentary layers, then intrusion, then fault Correct answer.
  2. Fault, then intrusion, then sedimentary layers
  3. Sedimentary layers, then fault, then intrusion
  4. Intrusion, then sedimentary layers, then fault

Explanation

Cross-cutting relationships show that the sedimentary layers were deposited first, the intrusion then cut them, and finally the fault displaced the intrusion. Each feature must be younger than the material it cuts.

Question 44Earth and Space Science (Level 3 achievement standards)

Two coastal locations at similar latitude have very different annual temperature ranges: one is small and the other is large. Which factor best explains this difference?

  1. The thermal inertia of nearby ocean water moderating coastal temperatures Correct answer.
  2. The presence of more greenhouse gases at one location
  3. The altitude of the observing station
  4. The distance of each location from the equator

Explanation

Water has a high specific heat capacity and heats and cools more slowly than land, so maritime locations have smaller annual temperature ranges. Continental interiors, lacking this moderating influence, show greater extremes.

Question 45Earth and Space Science (Level 3 achievement standards)

A rock layer contains 12.5 percent of its original radioactive parent isotope. How many half-lives have elapsed?

  1. 3 Correct answer.
  2. 4
  3. 2
  4. 1

Explanation

After each half-life, the fraction of parent remaining halves: 50 percent, 25 percent, 12.5 percent. Reaching 12.5 percent therefore requires three half-lives.

Question 46Earth and Space Science (Level 3 achievement standards)

A star's absorption spectrum shows lines shifted toward the blue compared with laboratory wavelengths. What does this indicate?

  1. The star is rotating rapidly
  2. The star is cooler than expected
  3. The star is moving away from the observer
  4. The star is moving toward the observer Correct answer.

Explanation

A blueshift means the observed wavelengths are shorter than the rest wavelengths, which occurs when the source approaches the observer due to the Doppler effect. A redshift would indicate recession.

Question 47Earth and Space Science (Level 3 achievement standards)

A subducting slab descends beneath a continental margin. Which feature is most likely to form above the descending slab at depth?

  1. A mid-ocean ridge
  2. A transform fault parallel to the coast
  3. A chain of andesitic volcanoes inland from the trench Correct answer.
  4. A broad sedimentary basin with no igneous activity

Explanation

Water released from the descending slab lowers the melting point of the overlying mantle wedge, generating magma that rises to form andesitic volcanoes inland from the trench. This volcanic arc is characteristic of subduction zones.

Question 48Earth and Space Science (Level 3 achievement standards)

An upper-level trough approaches a surface low-pressure centre. What is the most likely effect on the surface system?

  1. It intensifies because upper-level divergence supports rising air and lowers surface pressure Correct answer.
  2. It remains unchanged because upper and lower levels are independent
  3. It moves toward the equator without changing strength
  4. It weakens because upper-level convergence suppresses rising air

Explanation

An upper-level trough provides divergence aloft, which removes mass from the column and encourages ascent, lowering surface pressure and intensifying the low. This coupling between upper and lower levels is central to mid-latitude cyclone development.

Question 49Earth and Space Science (Level 3 achievement standards)

An ice core records a decrease in the ratio of oxygen-18 to oxygen-16 in layers dated to a glacial period. What is the best interpretation?

  1. Global temperatures were lower, so less heavy oxygen-18 was evaporated and transported to the ice Correct answer.
  2. The atmosphere contained more carbon dioxide at that time
  3. The ocean was warmer, increasing the oxygen-18 content of the ice
  4. The ice accumulated more rapidly during that period

Explanation

Lower temperatures reduce the evaporation and transport of the heavier oxygen-18 isotope, so glacial ice is relatively enriched in oxygen-16 and the oxygen-18 to oxygen-16 ratio falls. This isotope ratio is used as a temperature proxy.

Question 50Earth and Space Science (Level 3 achievement standards)

Two stars have the same apparent brightness, but star A is twice as far away as star B. How do their luminosities compare?

  1. Star A is four times more luminous than star B Correct answer.
  2. Star A is twice as luminous as star B
  3. Star A is half as luminous as star B
  4. Star A has the same luminosity as star B

Explanation

Apparent brightness falls with the square of distance, so a star twice as far must be four times more luminous to appear equally bright. This follows from the inverse-square law for radiation.