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NCEA Level 2 Earth and Space Science study materials
NCEA Level 2 Earth and Space Science study resources

NCEA Level 2 Earth and Space Science practice questions

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Question 1Earth and Space Science achievement standards (Level 2)

New Zealand lies on the boundary of the Pacific Plate and the Australian Plate. Which type of plate boundary passes through the South Island, producing the Southern Alps?

  1. A transform (conservative) boundary where plates slide past each other
  2. A convergent boundary where oceanic crust subducts beneath continental crust
  3. A convergent boundary where two continental plates collide and crust thickens Correct answer.
  4. A divergent boundary where new oceanic crust is created

Explanation

The Alpine Fault system is dominated by continental collision and transpression, where two pieces of continental crust are squeezed together. Continental crust is too buoyant to subduct easily, so it crumples and thickens, raising the Southern Alps. The strike-slip component explains the lateral offset, but the mountain building is driven by convergence.

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

A student records that a sample of basalt has a density of about 3.0 g/cm³, while continental granite is about 2.7 g/cm³. Which statement best explains why oceanic plates subduct beneath continental plates?

  1. Oceanic crust is hotter and therefore melts before continental crust
  2. Oceanic crust is denser and therefore sinks more readily into the mantle Correct answer.
  3. Continental crust is denser and therefore pushes oceanic crust downward
  4. Oceanic crust is thinner, so it is forced down by its own weight alone

Explanation

Subduction is driven mainly by density contrasts: the denser plate can sink into the mantle, while the more buoyant plate stays at the surface. Basalt is denser than granite, so oceanic lithosphere is the one that descends. Thickness and temperature influence behaviour but do not by themselves determine which plate goes down.

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

At a subduction zone, earthquakes occur along the descending plate. Which pattern best describes the depth of earthquake foci across a subduction zone?

  1. All earthquakes are shallow and confined to the top 20 km of crust
  2. Earthquakes occur only at a single fixed depth along the plate interface
  3. Earthquakes are deepest directly above the trench and shallowest far inland
  4. Earthquakes become progressively deeper inland, following the dipping slab Correct answer.

Explanation

The Wadati-Benioff zone traces the descending slab, so earthquake foci deepen as you move inland away from the trench. Shallow events cluster near the trench and deep events occur hundreds of kilometres beneath the volcanic arc and beyond. This dipping pattern is strong evidence for subduction.

Question 4Earth and Space Science achievement standards (Level 2)

A seismic station records P-waves and S-waves from the same earthquake. The S-wave arrives 24 seconds after the P-wave. Using the rule that the S–P time difference increases with distance, what does this time difference allow a seismologist to determine?

  1. The depth of the earthquake focus below the surface
  2. The magnitude of the earthquake on the Richter scale
  3. The type of fault that ruptured to produce the earthquake
  4. The distance from the station to the earthquake epicentre Correct answer.

Explanation

The S–P interval grows with distance because S-waves travel more slowly than P-waves, so the gap widens the further the waves travel. Converting that interval with a travel-time graph gives the epicentral distance for that station. Three such distances allow the epicentre to be located by triangulation.

Question 5Earth and Space Science achievement standards (Level 2)

Rhyolitic magma is much more viscous than basaltic magma. Which combination best explains why rhyolitic eruptions tend to be more explosive?

  1. High silica content, low viscosity and high dissolved gas content
  2. Low silica content, low viscosity and low dissolved gas content
  3. Low silica content, high viscosity and low dissolved gas content
  4. High silica content, high viscosity and high dissolved gas content Correct answer.

Explanation

Rhyolitic magma is silica-rich, which makes it polymerised and viscous, and it can hold a large volume of dissolved water and gas. Because the magma is sticky, gas cannot easily escape as it rises, so pressure builds until it fragments explosively. Basaltic magma is runnier and degasses more gently.

Question 6Earth and Space Science achievement standards (Level 2)

The Taupo Volcanic Zone in the North Island is associated with a subduction zone. What is the main reason magma is generated above the descending Pacific Plate?

  1. Friction melts the descending oceanic plate completely as it sinks
  2. The descending plate drags hot mantle rock upward to the surface
  3. Radioactive decay in the overriding plate melts the crust directly
  4. Water released from the slab lowers the melting point of the overlying mantle Correct answer.

Explanation

As the oceanic slab descends, it heats up and releases water and other volatiles. These fluids lower the melting temperature of the overlying mantle wedge, a process called flux melting. The resulting magma rises and feeds the arc volcanoes of the Taupo Volcanic Zone.

Question 7Earth and Space Science achievement standards (Level 2)

A map of the sea floor shows a mid-ocean ridge with matching magnetic stripes on either side. What does this pattern provide evidence for?

  1. A hotspot track, because the stripes record the movement of a mantle plume
  2. Continental collision, because the stripes are folded mountain belts
  3. Sea-floor spreading, with new crust recording reversals of Earth's magnetic field Correct answer.
  4. Subduction, because the stripes mark where old crust is being destroyed

Explanation

New basaltic crust forms at the ridge and cools, locking in the direction of Earth's magnetic field at that time. As the field reverses, symmetrical stripes of normal and reversed polarity form on each side of the ridge. This symmetry is key evidence that the sea floor is spreading outward from the ridge.

Question 8Earth and Space Science achievement standards (Level 2)

Which sequence correctly orders the stages in the formation of a sedimentary rock such as sandstone?

  1. Weathering, deposition, compaction and cementation Correct answer.
  2. Cementation, compaction, deposition, weathering
  3. Deposition, weathering, cementation, compaction
  4. Compaction, weathering, deposition, cementation

Explanation

Sedimentary rock forms after existing rock is broken down by weathering, and the debris is transported and deposited as sediment. Burial then compacts the sediment and cementation by minerals binds the grains into solid rock. The order of weathering, transport and deposition before lithification is essential.

Question 9Earth and Space Science achievement standards (Level 2)

A geologist finds a rock containing large crystals surrounded by much finer crystals. Which interpretation is most consistent with this texture?

  1. The magma cooled slowly at depth, then cooled rapidly after eruption Correct answer.
  2. The magma cooled slowly throughout, allowing all crystals to grow large
  3. The rock was formed by compaction of loose sediment grains
  4. The magma cooled rapidly throughout, producing only fine crystals

Explanation

A porphyritic texture records two cooling histories: large crystals grew slowly while the magma sat at depth, then the remaining melt cooled quickly after the magma moved or erupted, forming a fine groundmass. The size difference in crystals reflects the change in cooling rate.

Question 10Earth and Space Science achievement standards (Level 2)

Which statement correctly describes the difference between a mineral and a rock?

  1. A mineral is a naturally occurring inorganic solid with a definite chemical composition, while a rock is an aggregate of minerals Correct answer.
  2. A mineral is always formed by living organisms, while a rock is always inorganic
  3. A mineral is any substance found in the ground, while a rock is a single crystal of that substance
  4. A rock is a naturally occurring crystalline solid, while a mineral is a mixture of different rocks

Explanation

A mineral is defined as a naturally occurring, inorganic solid with an ordered atomic structure and a definite chemical composition. A rock is a solid aggregate of one or more minerals. This distinction separates a single crystalline substance such as quartz from a mixture such as granite.

Question 11Earth and Space Science achievement standards (Level 2)

A layer of sedimentary rock contains a fossil of a marine shell. The same rock layer is found on both sides of a valley. What does this indicate about the rock layers?

  1. The layers formed after the valley was eroded into the landscape
  2. The layers were deposited vertically and later tilted to horizontal
  3. The layers were originally deposited horizontally and were later cut by erosion Correct answer.
  4. The layers are igneous intrusions that flowed into the valley

Explanation

The principle of original horizontality states that sedimentary layers are laid down horizontally, and the principle of lateral continuity says they extend sideways until something interrupts them. Finding the same fossil-bearing layer on both sides of a valley means the layer once continued across the gap and the valley was later eroded through it. The matching fossil also supports correlation of the layer.

Question 12Earth and Space Science achievement standards (Level 2)

A geologist uses the principle of superposition when studying an undisturbed sequence of sedimentary rocks. What does this principle state?

  1. The oldest rocks are at the bottom and the youngest are at the top Correct answer.
  2. The rocks containing the most fossils are always the oldest
  3. The most intensely folded rocks are always the youngest
  4. The rocks with the largest grains are always the oldest

Explanation

Superposition applies to undisturbed sedimentary sequences, where each new layer is deposited on top of older layers. Therefore the lowest layer is the oldest and the highest is the youngest. Grain size and fossil abundance do not determine relative age in this way.

Question 13Earth and Space Science achievement standards (Level 2)

A rock sample contains a radioactive parent isotope with a half-life of 50 million years. Analysis shows that 25% of the parent isotope remains. How old is the sample, assuming no loss of parent or daughter isotope?

  1. 50 million years
  2. 100 million years Correct answer.
  3. 200 million years
  4. 75 million years

Explanation

After one half-life, 50% of the parent remains; after two half-lives, 25% remains. Two half-lives of 50 million years gives an age of 100 million years. The calculation uses the fraction remaining, not the number of daughter atoms directly.

Question 14Earth and Space Science achievement standards (Level 2)

Which feature of the New Zealand landscape is best explained by past glaciation rather than by river erosion?

  1. A narrow V-shaped valley cut into bedrock
  2. A meandering river with point bars on the inside of bends
  3. A steep-sided U-shaped valley with a hanging tributary valley Correct answer.
  4. A delta where a river enters the sea

Explanation

Glaciers erode broad U-shaped troughs because ice grinds the sides as well as the floor, and tributary glaciers erode less deeply, leaving hanging valleys. Rivers cut narrow V-shaped valleys and form meanders and deltas. The U-shape and hanging valleys are classic glacial signatures.

Question 15Earth and Space Science achievement standards (Level 2)

Which combination of factors most increases the risk of a slope failure on a steep hillside?

  1. Low rainfall, gentle slope and dense vegetation
  2. Dry soil, flat ground and a thick root layer
  3. Heavy rainfall, steep slope and removal of vegetation Correct answer.
  4. Low groundwater, gentle slope and compacted rock

Explanation

Slope failure is more likely when the driving stress exceeds the resisting strength of the material. Heavy rain raises pore-water pressure and adds weight, steep slopes increase the downslope component of gravity, and removing vegetation reduces root reinforcement. Together these factors strongly raise landslide risk.

Question 16Earth and Space Science achievement standards (Level 2)

A river flows from a steep mountain gorge onto a flat plain. Which change in the river's behaviour is expected as it enters the plain?

  1. It stops carrying any sediment and becomes completely clear
  2. It increases its gradient and erodes its banks more strongly
  3. It slows down and deposits sediment, forming an alluvial fan Correct answer.
  4. It speeds up and cuts a deeper V-shaped gorge

Explanation

When a river leaves a steep gorge and enters a flat plain, the gradient drops and the flow slows. The reduced velocity lowers its competence to carry sediment, so material is deposited where the slope changes, building an alluvial fan. The river does not speed up or cut more deeply under these conditions.

Question 17Earth and Space Science achievement standards (Level 2)

The ocean absorbs a large share of the carbon dioxide released by burning fossil fuels. What is a direct consequence of this uptake for the ocean?

  1. Ocean water becomes more alkaline as carbonate increases
  2. Ocean salinity rises sharply because of the added carbon
  3. Ocean water becomes more acidic as carbonic acid forms Correct answer.
  4. Ocean temperature falls rapidly because carbon dioxide cools water

Explanation

Dissolved carbon dioxide reacts with water to form carbonic acid, which releases hydrogen ions and lowers pH. This process, called ocean acidification, reduces the availability of carbonate ions that many marine organisms need to build shells. The change is a shift toward more acidic conditions, not more alkaline ones.

Question 18Earth and Space Science achievement standards (Level 2)

Which statement best describes the role of the ocean in moderating Earth's climate?

  1. The ocean has a high heat capacity and stores and transports large amounts of heat Correct answer.
  2. The ocean has a low heat capacity and changes temperature very quickly
  3. The ocean prevents any heat from moving between the tropics and the poles
  4. The ocean reflects most incoming sunlight because of its high albedo

Explanation

Water has a high specific heat capacity, so the ocean absorbs and stores large amounts of heat with only small temperature changes. Ocean currents then move that heat around the globe, moderating coastal climates and transferring energy from the tropics toward the poles. This makes the ocean a major regulator of climate.

Question 19Earth and Space Science achievement standards (Level 2)

During a strong El Niño event, the trade winds weaken and warm surface water spreads eastward across the equatorial Pacific. What weather effect is typically observed in New Zealand?

  1. No measurable change in wind or rainfall patterns
  2. Cooler sea temperatures and more southerly winds
  3. More frequent droughts in the east and stronger westerly winds Correct answer.
  4. Increased rainfall in the east and weaker westerly winds

Explanation

El Niño alters the position of the atmospheric pressure systems over the Pacific, strengthening westerly winds over New Zealand. These winds bring drier conditions to eastern regions and more rain to the west, so droughts become more likely in the east. The pattern is a well-documented seasonal climate signal.

Question 20Earth and Space Science achievement standards (Level 2)

Which process transfers heat through the movement of a fluid such as magma or air?

  1. Radiation
  2. Reflection
  3. Conduction
  4. Convection Correct answer.

Explanation

Convection transfers heat when a fluid moves, carrying warmer material from one place to another. In Earth science, mantle convection and atmospheric convection are both important heat-transfer mechanisms. Conduction works through direct contact and radiation travels as electromagnetic waves.

Question 21Earth and Space Science achievement standards (Level 2)

Earth's magnetic field is generated by motion in the outer core. Which process is responsible for this magnetic field?

  1. The movement of tectonic plates across the mantle
  2. Convection of liquid iron in the outer core, acting as a geodynamo Correct answer.
  3. The solid inner core rotating as a permanent magnet
  4. The flow of charged particles in the atmosphere

Explanation

The outer core is liquid iron and nickel, and convection driven by heat from the inner core sets up electric currents. These currents generate the magnetic field through a dynamo process. The field is not produced by the solid inner core alone or by plate motion.

Question 22Earth and Space Science achievement standards (Level 2)

Seismic waves change speed and direction as they pass through Earth's interior. What does the existence of an S-wave shadow zone reveal about the outer core?

  1. The outer core is liquid because S-waves cannot pass through it Correct answer.
  2. The outer core is gaseous because S-waves are absorbed there
  3. The outer core is solid because S-waves speed up there
  4. The outer core is crystalline because S-waves are refracted there

Explanation

S-waves are shear waves and cannot travel through liquids. The S-wave shadow zone beyond about 103° from the epicentre shows that S-waves are blocked by a liquid layer, which is the outer core. P-waves are also refracted by the core, but they can pass through it.

Question 23Earth and Space Science achievement standards (Level 2)

Which statement best explains why the Moon shows phases such as crescent and gibbous?

  1. The Moon's distance from Earth changes, altering its apparent shape
  2. The amount of the sunlit half visible from Earth changes as the Moon orbits Correct answer.
  3. The Moon rotates on its axis faster than it orbits Earth
  4. Earth's shadow falls on different parts of the Moon during the month

Explanation

Half of the Moon is always lit by the Sun, but the proportion of that lit half facing Earth changes as the Moon orbits. This changing view produces the phases from new Moon through crescent, quarter, gibbous and full Moon. The phases are not caused by Earth's shadow, which produces lunar eclipses.

Question 24Earth and Space Science achievement standards (Level 2)

The apparent positions of stars change slightly over the year because Earth orbits the Sun. What is the name of this effect?

  1. Precession of the equinoxes
  2. Doppler shift
  3. Stellar parallax Correct answer.
  4. Aberration of starlight

Explanation

As Earth moves from one side of its orbit to the other, nearby stars appear to shift against more distant background stars. This annual shift is called stellar parallax, and the angle measured can be used to determine a star's distance. Precession and aberration are different effects.

Question 25Earth and Space Science achievement standards (Level 2)

A star's spectrum shows its absorption lines shifted toward the red end compared with laboratory wavelengths. What can be concluded about the star?

  1. It is rotating rapidly on its axis
  2. It is much cooler than the Sun
  3. It is moving toward the observer
  4. It is moving away from the observer Correct answer.

Explanation

A redshift means the observed wavelengths are longer than the rest wavelengths, which happens when the source moves away from the observer. This is the Doppler effect applied to light. A blueshift would indicate motion toward the observer.

Question 26Earth and Space Science achievement standards (Level 2)

A geologist finds a dark, fine-grained igneous rock with no visible crystals. Which conclusion about its cooling history is most consistent with this texture?

  1. It cooled slowly deep underground, allowing large crystals to form.
  2. It cooled slowly and then was reheated, which removed the crystals.
  3. It was metamorphosed under high pressure, which destroyed all crystals.
  4. It cooled rapidly at or near Earth's surface, preventing crystal growth. Correct answer.

Explanation

Fine-grained igneous rocks form when magma or lava cools quickly, so crystals do not have time to grow large. Slow cooling deep underground produces coarse-grained rocks. Metamorphism and reheating would not typically erase all crystals in this way.

Question 27Earth and Space Science achievement standards (Level 2)

A sedimentary rock layer contains fossils of identical marine shells on two continents now separated by a wide ocean. Which explanation best accounts for this observation?

  1. The two continents were once joined and have since moved apart. Correct answer.
  2. The fossils were deposited by glaciers that covered both continents.
  3. The shells were carried across the ocean by ocean currents after the continents separated.
  4. The shells evolved independently on each continent at the same time.

Explanation

Matching fossils on now-separated continents are strong evidence that the landmasses were once connected. The organisms lived in the same region before continental drift moved the continents apart. Independent evolution or ocean currents are less likely to produce identical fossils in the same rock layers.

Question 28Earth and Space Science achievement standards (Level 2)

Which statement best describes how the fossil record provides evidence for biological evolution?

  1. Fossils show a sequence of change in organisms over geological time, with many transitional forms. Correct answer.
  2. Fossils show that simpler organisms always replace more complex ones in every rock layer.
  3. Fossils prove that all organisms were created at the same time and have not changed.
  4. Fossils show a random assortment of organisms with no pattern over time.

Explanation

The fossil record reveals a progression of life forms through geological time, including transitional fossils that link ancestral and descendant groups. This pattern supports the idea that species change over time. Fossils do not show random assortment or unchanging species.

Question 29Earth and Space Science achievement standards (Level 2)

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

  1. The epicentre is the point on the opposite side of Earth from the focus.
  2. The epicentre is the underground point where the earthquake starts, and the focus is the surface point above it.
  3. The epicentre is the point on Earth's surface directly above the focus, where the earthquake originates underground. Correct answer.
  4. The epicentre and focus are the same point, located at the surface.

Explanation

The focus (hypocentre) is the underground location where an earthquake rupture begins. The epicentre is the point on the surface directly above the focus. They are not the same point, and the epicentre is not on the opposite side of Earth.

Question 30Earth and Space Science achievement standards (Level 2)

Which statement best explains why the Moon always shows the same face to Earth?

  1. The Moon does not rotate on its axis.
  2. Earth's gravity prevents the Moon from rotating.
  3. The Moon rotates twice for every orbit around Earth.
  4. The Moon rotates once on its axis in the same time it takes to orbit Earth. Correct answer.

Explanation

The Moon is in synchronous rotation: it rotates once on its axis during each orbit around Earth. This means the same side always faces Earth. It does rotate, but the rotation period matches the orbital period.

Question 31Earth and Space Science achievement standards (Level 2)

Which process is primarily responsible for the formation of the ozone layer in the stratosphere?

  1. Ozone is created by the condensation of water vapour at high altitudes.
  2. Volcanic eruptions release ozone directly into the stratosphere.
  3. Oxygen molecules are split by ultraviolet radiation and recombine to form ozone. Correct answer.
  4. Ozone is produced by the burning of fossil fuels at ground level and rises.

Explanation

In the stratosphere, ultraviolet radiation splits oxygen molecules (O2) into single oxygen atoms. These atoms combine with other O2 molecules to form ozone (O3). This photochemical process creates the ozone layer.

Question 32Earth and Space Science achievement standards (Level 2)

Which statement best explains why the greenhouse effect is essential for life on Earth?

  1. It completely blocks incoming solar radiation, preventing overheating.
  2. It reflects all outgoing radiation back to space, cooling the planet.
  3. It increases the amount of solar radiation reaching Earth's surface.
  4. It traps some outgoing infrared radiation, keeping Earth's surface warmer than it would otherwise be. Correct answer.

Explanation

Greenhouse gases absorb and re-emit infrared radiation emitted by Earth's surface, trapping heat in the atmosphere. This natural greenhouse effect raises the average surface temperature to a level suitable for life. It does not block incoming solar radiation or increase it.

Question 33Earth and Space Science achievement standards (Level 2)

Which statement correctly describes the relationship between the rotation of Earth and the apparent movement of stars across the night sky?

  1. Stars move from west to east because Earth rotates from east to west.
  2. Earth's rotation on its axis once per day causes stars to appear to move from east to west. Correct answer.
  3. The apparent motion of stars is caused by the Moon's gravitational pull.
  4. Stars orbit Earth once per year, causing their apparent nightly motion.

Explanation

Earth rotates from west to east on its axis once every 24 hours. This makes stars appear to move across the sky from east to west. The stars are not orbiting Earth; their apparent motion is due to Earth's rotation.

Question 34Earth and Space Science achievement standards (Level 2)

A geologist observes a sequence of sedimentary rocks where a layer of conglomerate is overlain by sandstone, which is in turn overlain by mudstone. Using the principle of superposition, what can be concluded about the relative ages of these layers?

  1. The conglomerate is the oldest, and the mudstone is the youngest. Correct answer.
  2. The mudstone is the oldest because it is at the top.
  3. The conglomerate is the youngest because it is at the bottom.
  4. All layers are the same age because they are in the same sequence.

Explanation

The principle of superposition states that in an undisturbed sequence of sedimentary rocks, the oldest layers are at the bottom and the youngest at the top. Therefore, the conglomerate at the base is oldest, and the mudstone at the top is youngest.

Question 35Earth and Space Science achievement standards (Level 2)

A radioactive isotope has a half-life of 200 million years. A mineral sample contains 12.5% of the original parent isotope. How many half-lives have elapsed, and what is the approximate age of the sample?

  1. 3 half-lives; 600 million years Correct answer.
  2. 4 half-lives; 800 million years
  3. 2 half-lives; 400 million years
  4. 1 half-life; 200 million years

Explanation

After one half-life, 50% parent remains; after two, 25%; after three, 12.5%. Thus three half-lives have passed. With a half-life of 200 million years, the age is 3 × 200 = 600 million years.

Question 36Earth and Space Science achievement standards (Level 2)

Which feature of a landscape provides the best evidence that a glacier has flowed over the area in the past?

  1. A delta at the mouth of a river where it enters a lake
  2. A U-shaped valley with a broad, flat floor and steep walls Correct answer.
  3. A V-shaped valley with a narrow floor and steep sides
  4. A meandering river with point bars and cut banks

Explanation

Glaciers erode U-shaped valleys with wide, flat floors and steep sides. Rivers typically erode V-shaped valleys. Meanders and deltas are features of river deposition, not glacial erosion.

Question 37Earth and Space Science achievement standards (Level 2)

A steep hillside composed of loose, unconsolidated volcanic ash receives heavy rainfall over several days. Which factor most directly increases the risk of a slope failure?

  1. The ash layer becomes saturated with water, reducing friction between particles. Correct answer.
  2. The rainfall washes away the vegetation, which increases root strength.
  3. The ash absorbs water and expands, increasing friction.
  4. The rainfall cools the ash, making it contract and crack.

Explanation

Water saturates the loose ash, increasing pore water pressure and reducing the effective friction between particles. This decreases slope stability and can trigger a landslide. Vegetation removal reduces root strength, but the direct cause here is saturation and loss of friction.

Question 38Earth and Space Science achievement standards (Level 2)

A river emerges from a steep mountain gorge onto a flat plain. Which change in river behaviour is most likely to occur?

  1. The river will deposit sediment, forming an alluvial fan. Correct answer.
  2. The river will increase its velocity and cut a V-shaped valley.
  3. The river will become a braided stream with no deposition.
  4. The river will erode more deeply, forming a narrow canyon.

Explanation

When a river flows from a steep gradient onto a flat plain, its velocity decreases, reducing its carrying capacity. Sediment is deposited, often forming an alluvial fan. The river does not erode more deeply or increase velocity in this situation.

Question 39Earth and Space Science achievement standards (Level 2)

The ocean absorbs a large amount of carbon dioxide from the atmosphere. What is a direct consequence of this absorption for ocean chemistry?

  1. The ocean becomes more acidic, lowering its pH. Correct answer.
  2. The ocean's temperature increases uniformly.
  3. The ocean becomes more alkaline, raising its pH.
  4. The ocean's salinity decreases significantly.

Explanation

Carbon dioxide dissolves in seawater to form carbonic acid, which releases hydrogen ions and lowers pH. This process, known as ocean acidification, makes the ocean more acidic. It does not significantly change salinity or uniformly raise temperature.

Question 40Earth and Space Science achievement standards (Level 2)

Which statement best explains how the ocean moderates Earth's climate?

  1. The ocean has a high heat capacity and transports heat through currents, reducing temperature extremes. Correct answer.
  2. The ocean releases large amounts of heat into the atmosphere during winter, causing global cooling.
  3. The ocean reflects most incoming solar radiation back to space.
  4. The ocean absorbs all incoming solar radiation, preventing any heat from reaching the atmosphere.

Explanation

Water has a high specific heat capacity, so the ocean absorbs and stores large amounts of heat with little temperature change. Ocean currents redistribute this heat around the globe, moderating temperature extremes between seasons and latitudes. The ocean does not reflect most solar radiation or absorb all of it.

Question 41Earth and Space Science achievement standards (Level 2)

During a strong El Niño event, the trade winds weaken and warm surface water spreads eastward across the equatorial Pacific. Which effect is most likely to occur?

  1. Increased upwelling of cold, nutrient-rich water off the coast of South America
  2. Decreased rainfall in the central Pacific and increased rainfall in Australia
  3. Cooler sea surface temperatures in the eastern Pacific
  4. Drought conditions in Australia and flooding in Peru Correct answer.

Explanation

El Niño weakens the trade winds, reducing upwelling of cold water in the eastern Pacific and allowing warm water to spread eastward. This shift in atmospheric circulation often brings drought to Australia and heavy rainfall and flooding to Peru. Upwelling decreases, not increases.

Question 42Earth and Space Science achievement standards (Level 2)

Seismic waves change speed and direction as they pass through Earth's interior. What does the existence of an S-wave shadow zone indicate about Earth's outer core?

  1. The outer core has the same composition as the mantle.
  2. The outer core is solid because S-waves cannot pass through solids.
  3. The outer core is gaseous because S-waves are absorbed by gases.
  4. The outer core is liquid because S-waves cannot pass through liquids. Correct answer.

Explanation

S-waves (shear waves) cannot travel through liquids. The S-wave shadow zone is evidence that the outer core is liquid, as S-waves are not detected in certain regions beyond the core. This helps define the liquid outer core.

Question 43Earth and Space Science achievement standards (Level 2)

A star's spectrum shows its absorption lines shifted toward the red end compared with laboratory wavelengths. What can be inferred about the star's motion?

  1. The star is rotating rapidly.
  2. The star is stationary relative to Earth.
  3. The star is moving away from Earth. Correct answer.
  4. The star is moving toward Earth.

Explanation

A redshift in a star's spectrum indicates that the star is moving away from the observer, due to the Doppler effect. A blueshift would indicate motion toward Earth. The shift is not caused by rotation alone.

Question 44Earth and Space Science achievement standards (Level 2)

A sedimentary rock layer contains a fossil of a marine shell. The same rock layer is found on both sides of a valley. What does this most likely indicate about the geological history of the area?

  1. The shell was carried into the valley by wind after the valley formed.
  2. The two sides of the valley have different ages and origins.
  3. The rock layer was once continuous across the area and was later cut by the valley. Correct answer.
  4. The valley was formed by a glacier that deposited the shell.

Explanation

Finding the same fossil-bearing rock layer on both sides of a valley suggests that the layer was originally continuous. The valley was later eroded through the layer, separating it into two parts. This is an application of the principle of lateral continuity.

Question 45Earth and Space Science achievement standards (Level 2)

A layer of sedimentary rock contains a fossil of a marine shell. The same rock layer is found on both sides of a valley. Which principle best explains this observation?

  1. The principle of cross-cutting relationships
  2. The principle of lateral continuity Correct answer.
  3. The principle of original horizontality
  4. The principle of superposition

Explanation

The principle of lateral continuity states that sedimentary layers originally extend laterally in all directions until they thin or encounter a barrier. Finding the same layer on both sides of a valley supports this principle, as the valley eroded through a once-continuous layer.

Question 46Earth and Space Science achievement standards (Level 2)

Which layer of Earth's interior is composed mainly of solid iron and nickel and is under the greatest pressure?

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

Explanation

The inner core is solid iron-nickel despite extremely high temperatures because the pressure from overlying layers keeps it solid. The outer core is liquid iron-nickel, the mantle is silicate rock, and the crust is thin and rocky.

Question 47Earth and Space Science achievement standards (Level 2)

Which type of plate boundary is marked by two plates moving apart, with new oceanic crust forming between them?

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

Explanation

At a divergent boundary, plates move apart and magma rises to fill the gap, creating new crust such as along the Mid-Atlantic Ridge. Convergent boundaries involve plates colliding, transform boundaries involve lateral sliding, and subduction is a form of convergence.

Question 48Earth and Space Science achievement standards (Level 2)

Which gas makes up the largest proportion of Earth's current atmosphere?

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

Explanation

Nitrogen makes up roughly 78% of the atmosphere by volume, making it the most abundant gas. Oxygen is about 21%, argon under 1%, and carbon dioxide only about 0.04%.

Question 49Earth and Space Science achievement standards (Level 2)

Which term describes the boundary where a stream flows into a larger body of water such as a lake or ocean?

  1. The watershed
  2. The tributary
  3. The source
  4. The mouth Correct answer.

Explanation

A river's mouth is the point where it discharges into a larger water body, often forming a delta or estuary. The source is where it begins, a tributary is a feeder stream, and a watershed is the whole drainage area.

Question 50Earth and Space Science achievement standards (Level 2)

Which process transfers heat through the bulk movement of a fluid such as magma or air?

  1. Radiation
  2. Reflection
  3. Convection Correct answer.
  4. Conduction

Explanation

Convection moves heat by the physical circulation of a fluid: warmer, less dense material rises while cooler material sinks. Conduction passes heat through direct contact without bulk flow, radiation travels as electromagnetic waves, and reflection is the bouncing of waves rather than heat transfer.