Earth & Space Science — Final exam worked answers

Question 1 · 1 point

Three readings are 8, 10, and 12 mm. Find their mean.

Worked answer

10 mm

(8 + 10 + 12) ÷ 3 = 10.

1 point for the correct objective answer; no written-method marks for this item.

Question 2 · 1 point

Repeated measurements that agree closely with each other but differ from a known standard are

1. accurate but imprecise
2. precise but inaccurate
3. both accurate and precise
4. neither

Worked answer

precise but inaccurate

Agreement among repeats is precision; agreement with the standard is accuracy.

1 point for the correct objective answer; no written-method marks for this item.

Question 3 · 1 point

Contour lines drawn close together indicate

1. a gentle slope
2. a steep slope
3. flat ground
4. a lake

Worked answer

a steep slope

The same elevation change over a shorter horizontal distance is a steeper gradient.

1 point for the correct objective answer; no written-method marks for this item.

Question 4 · 3 points

A contour map rises from 240 m to 540 m over 6 km horizontally. Find gradient and state why a winding trail can have a different length.

Worked answer

50 m/km; trail length follows bends and need not equal horizontal map separation.

Rise=300 m; gradient=300/6.

Horizontal straight-line separation differs from the route along a trail.

Marking criteria

• 1 point: elevation difference.
• 1 point: gradient with units.
• 1 point: distinguish route length from horizontal separation.

Question 5 · 3 points

A gauge gives rainfall values 28, 30 and 32 mm. Find mean and range; explain why these readings do not rule out a calibration error.

Worked answer

Mean 30 mm, range 28–32 mm; compare with a calibrated reference to check accuracy.

Mean=90/3=30 mm; range 28–32 mm.

Repeated readings can share the same systematic offset.

Marking criteria

• 1 point: correct mean.
• 1 point: correct range.
• 1 point: systematic-error explanation and valid check.

Question 6 · 1 point

Which is the thin, solid, outermost layer of the Earth, where we live?

1. The crust
2. The mantle
3. The outer core
4. The inner core

Worked answer

The crust

The crust is Earth's thin, rocky, solid outer layer. Below it lie the thick mantle and the metallic core.

1 point for the correct objective answer; no written-method marks for this item.

Question 7 · 1 point

The outer core is inferred to be liquid because

1. it is the hottest layer
2. S-waves do not pass through it
3. it is closest to the surface
4. it contains water

Worked answer

S-waves do not pass through it

S-waves cannot travel through liquid, producing a shadow zone.

1 point for the correct objective answer; no written-method marks for this item.

Question 8 · 1 point

New ocean floor is created at

1. subduction zones
2. mid-ocean ridges
3. transform faults
4. continental interiors

Worked answer

mid-ocean ridges

Magma rises at the ridge and solidifies as the plates separate.

1 point for the correct objective answer; no written-method marks for this item.

Question 9 · 1 point

Symmetrical magnetic stripes either side of a mid-ocean ridge are evidence of

1. a static sea floor
2. sea-floor spreading
3. meteorite impacts
4. ocean currents

Worked answer

sea-floor spreading

Each stripe records the field direction when that crust formed, mirrored as it spread both ways.

1 point for the correct objective answer; no written-method marks for this item.

Question 10 · 3 points

Ocean-floor rocks become older away from a ridge on both sides and have mirrored magnetic patterns. Explain the plate process and why combining evidence helps.

Worked answer

Seafloor spreading explains both patterns; agreement across independent observations strengthens the model.

New crust forms at the ridge and moves outward.

Symmetric age and magnetic records independently fit spreading.

Marking criteria

• 1 point: new crust at a divergent ridge.
• 1 point: outward movement explaining age pattern.
• 1 point: magnetic evidence and independent-evidence reasoning.

Question 11 · 3 points

Two towns have comparable earthquake shaking hazard but different building strength and population density. Explain risk differences and propose a mitigation with a limit.

Worked answer

The crowded town with weak buildings may have higher risk; reinforcing structures can reduce damage, while shaking hazard remains.

Risk includes exposure and vulnerability as well as hazard.

Reinforcement reduces vulnerability but does not prevent plate movement.

Marking criteria

• 1 point: distinguish hazard, exposure and vulnerability.
• 1 point: supported risk comparison.
• 1 point: mitigation linked to vulnerability and a valid limit.

Question 12 · 1 point

Which of these is NOT one of the five traits required for a substance to be classified as a mineral?

1. Naturally occurring
2. Made of living tissue
3. A solid
4. Definite chemical composition

Worked answer

Made of living tissue

Minerals must be inorganic — not created by living organisms; the other three are indeed required traits.

1 point for the correct objective answer; no written-method marks for this item.

Question 13 · 1 point

Streak is a more reliable identifier than colour because streak

1. is easier to see
2. is unaffected by most impurities
3. changes with light
4. measures hardness

Worked answer

is unaffected by most impurities

The powdered colour stays consistent while surface colour varies.

1 point for the correct objective answer; no written-method marks for this item.

Question 14 · 1 point

Large interlocking crystals in an igneous rock indicate the magma cooled

1. rapidly at the surface
2. slowly underground
3. in water
4. without minerals

Worked answer

slowly underground

Slow cooling gives crystals time to grow.

1 point for the correct objective answer; no written-method marks for this item.

Question 15 · 1 point

Breaking rock into smaller fragments speeds chemical weathering because it increases

1. the mass
2. the total surface area exposed
3. the density
4. the hardness

Worked answer

the total surface area exposed

More surface is in contact with water and air.

1 point for the correct objective answer; no written-method marks for this item.

Question 16 · 3 points

A basin receives 200 water units, loses 130 naturally and has 50 withdrawn. Calculate storage change; explain why high porosity alone does not prove rapid groundwater flow.

Worked answer

Storage rises by 20 units in the defined model; porous material can still have low permeability.

Output=130+50=180; change=200−180.

Flow depends on connected pores and fractures, or permeability.

Marking criteria

• 1 point: complete budget calculation.
• 1 point: storage increase with supplied units.
• 1 point: porosity/permeability distinction.

Question 17 · 3 points

A stream slows entering a lake and deposits coarse grains before fine grains. Explain the process and why color alone cannot identify a sampled rock.

Worked answer

Sorting and deposition fit the pattern; a unique rock name requires more than color.

Reduced flow lowers sediment transport capacity.

Deposition depends on particle size, density and shape; rock identification needs texture and mineral evidence.

Marking criteria

• 1 point: erosion/transport versus deposition distinction.
• 1 point: flow and grain explanation with a relevant condition.
• 1 point: multiple-property identification reasoning.

Question 18 · 1 point

Which lists the units of the geologic time scale from LARGEST to smallest?

1. Eon, era, period
2. Period, era, eon
3. Era, eon, period
4. Period, eon, era

Worked answer

Eon, era, period

Eons are the biggest divisions, then eras, then periods — like books, chapters, and pages.

1 point for the correct objective answer; no written-method marks for this item.

Question 19 · 1 point

A fault that cuts through several rock layers must be

1. older than all of them
2. younger than the layers it cuts
3. the same age
4. undatable

Worked answer

younger than the layers it cuts

A feature must exist before it can be cut.

1 point for the correct objective answer; no written-method marks for this item.

Question 20 · 1 point

After three half-lives, the percentage of original parent isotope remaining is

1. 33
2. 25
3. 12.5
4. 6.25

Worked answer

12.5

100 → 50 → 25 → 12.5 percent.

1 point for the correct objective answer; no written-method marks for this item.

Question 21 · 1 point

The most useful index fossil comes from a species that was

1. long-lived and local
2. short-lived and widespread
3. still alive today
4. rare everywhere

Worked answer

short-lived and widespread

A narrow time range gives precision and wide distribution allows correlation.

1 point for the correct objective answer; no written-method marks for this item.

Question 22 · 3 points

Beds A, B and C lie bottom to top, an intrusion cuts all three and a fault cuts the intrusion. Order events and explain what an unconformity would indicate.

Worked answer

The fault is youngest; an unconformity represents missing time from erosion or nondeposition, not a known duration from order alone.

Use superposition and cross-cutting relationships.

A→B→C→intrusion→fault under undeformed-bed assumptions.

Marking criteria

• 1 point: bed order.
• 1 point: intrusion then fault.
• 1 point: unconformity and relative/numerical-age distinction.

Question 23 · 3 points

A closed mineral retains 12.5% of its original parent isotope. Half-life is 5 million years. Calculate age and state two dating assumptions.

Worked answer

15 million years; mineral crystallization age need not equal the deposition age of a later sediment containing it.

100→50→25→12.5 is three half-lives.

3×5=15 million years; require known initial conditions and retained relevant isotopes.

Marking criteria

• 1 point: three half-lives.
• 1 point: 15 million-year age.
• 1 point: two valid assumptions or dating-event limitations.

Question 24 · 1 point

Which process changes liquid water into water vapor, mostly from the surface of the ocean?

1. Evaporation
2. Condensation
3. Precipitation
4. Infiltration

Worked answer

Evaporation

The sun's energy heats liquid water until it evaporates into invisible water vapor.

1 point for the correct objective answer; no written-method marks for this item.

Question 25 · 1 point

Paving over a field most directly increases

1. infiltration
2. surface runoff
3. transpiration
4. groundwater recharge

Worked answer

surface runoff

Water cannot soak in, so more flows across the surface.

1 point for the correct objective answer; no written-method marks for this item.

Question 26 · 1 point

Closely spaced isobars on a weather map indicate

1. light winds
2. strong winds
3. no wind
4. high temperature

Worked answer

strong winds

A steep pressure gradient drives faster wind.

1 point for the correct objective answer; no written-method marks for this item.

Question 27 · 1 point

When air temperature equals the dew point, the relative humidity is

1. 0 percent
2. 50 percent
3. 100 percent
4. undefined

Worked answer

100 percent

The air is saturated, so condensation begins.

1 point for the correct objective answer; no written-method marks for this item.

Question 28 · 3 points

A front moves 240 km between maps 8 h apart. Find mean speed and explain why that alone does not give an exact later arrival time.

Worked answer

30 km/h over the observed interval; further observations are needed for a reliable arrival estimate.

Speed=240/8=30 km/h.

Later speed and direction can change; local weather and position also matter.

Marking criteria

• 1 point: speed method.
• 1 point: value with units.
• 1 point: valid extrapolation limitation.

Question 29 · 3 points

A dark and light surface warm differently in sunlight. Design a controlled comparison and explain why this small test does not fully explain global winds.

Worked answer

A repeated controlled surface test can isolate an albedo-related mechanism, while global circulation needs a larger model.

Match material, size, starting temperature, sunlight and measurement method.

Different absorption can change warming; global circulation also depends on rotation, geography and pressure gradients.

Marking criteria

• 1 point: fair controlled design.
• 1 point: absorption/energy mechanism.
• 1 point: global-model limitation naming another factor.

Question 30 · 1 point

Which statement correctly describes the difference between weather and climate?

1. Weather is day-to-day conditions; climate is the long-term average pattern.
2. Weather and climate mean the same thing.
3. Climate changes every hour; weather stays the same for decades.
4. Weather only applies to storms; climate applies to sunny days.

Worked answer

Weather is day-to-day conditions; climate is the long-term average pattern.

Weather is short-term (today's conditions); climate is the long-term average over decades.

1 point for the correct objective answer; no written-method marks for this item.

Question 31 · 1 point

Greenhouse gases warm the surface because they

1. block incoming sunlight
2. absorb and re-emit outgoing infrared radiation
3. cool the upper atmosphere only
4. reflect sunlight

Worked answer

absorb and re-emit outgoing infrared radiation

They are largely transparent to sunlight but absorb the infrared Earth radiates.

1 point for the correct objective answer; no written-method marks for this item.

Question 32 · 1 point

Deep ocean circulation is driven mainly by differences in

1. wave height
2. temperature and salinity, and so density
3. tides
4. wind alone

Worked answer

temperature and salinity, and so density

Cold salty water is dense and sinks, driving the overturning.

1 point for the correct objective answer; no written-method marks for this item.

Question 33 · 1 point

Melting sea ice exposing darker ocean is an example of

1. negative feedback
2. positive feedback
3. no feedback
4. a carbon sink

Worked answer

positive feedback

Darker water absorbs more energy, causing further melting.

1 point for the correct objective answer; no written-method marks for this item.

Question 34 · 3 points

An annual mean is 15°C. Two graph baselines are 13°C and 14°C. Calculate both anomalies and explain why a baseline change does not change the measured temperature.

Worked answer

+2°C and +1°C respectively; the actual annual mean remains 15°C.

Subtract the stated baseline: 15−13 and 15−14.

A reference shift changes plotted differences, not underlying measurements.

Marking criteria

• 1 point: anomaly definition.
• 1 point: both values with units.
• 1 point: baseline versus underlying-measurement distinction.

Question 35 · 3 points

Warming reduces reflective ice cover and increases absorbed sunlight. Identify the feedback; explain why one cold local day does not test the whole climate trend.

Worked answer

A positive feedback; a cold day can coexist with a long-term warming pattern.

Ice loss lowers albedo and reinforces warming.

Long-term climate trends use many times and locations, not one weather event.

Marking criteria

• 1 point: correctly trace the albedo mechanism.
• 1 point: positive feedback means amplification.
• 1 point: weather/climate scale distinction.

Question 36 · 1 point

What actually causes the Moon's phases?

1. Earth's shadow falls on the Moon
2. Different amounts of the Moon's sunlit half face Earth as it orbits
3. The Moon changes how much light it produces
4. Clouds on Earth block our view of the Moon

Worked answer

Different amounts of the Moon's sunlit half face Earth as it orbits

Half the Moon is always lit by the Sun; phases come from how much of that lit half faces Earth as the Moon orbits us.

1 point for the correct objective answer; no written-method marks for this item.

Question 37 · 1 point

Moon phases are caused by

1. Earth's shadow
2. the changing angle from which we see the Moon's sunlit half
3. clouds
4. the Moon's own light

Worked answer

the changing angle from which we see the Moon's sunlit half

Half the Moon is always lit; the phase is how much of that half faces Earth.

1 point for the correct objective answer; no written-method marks for this item.

Question 38 · 1 point

Earth is closest to the Sun in early January. This shows that seasons are not caused mainly by

1. axial tilt
2. distance from the Sun
3. day length
4. sunlight angle

Worked answer

distance from the Sun

The northern hemisphere has winter then, so distance cannot be the cause.

1 point for the correct objective answer; no written-method marks for this item.

Question 39 · 1 point

Astronauts float on a space station because they and the station are

1. beyond Earth's gravity
2. falling freely around Earth together
3. weightless objects
4. shielded from gravity

Worked answer

falling freely around Earth together

Gravity is still strong in low orbit; continuous free fall produces the floating.

1 point for the correct objective answer; no written-method marks for this item.

Question 40 · 3 points

Explain why full moons are usually not eclipsed and why opposite hemispheres have opposite seasons.

Worked answer

Orbital tilt limits eclipses; Earth's tilt, rather than changing Sun distance, explains opposite seasons.

The lunar orbit's tilt usually prevents passage through Earth's shadow.

Earth's axial tilt changes day length and Sun angle in opposite hemispheres.

Marking criteria

• 1 point: phase/eclipse distinction.
• 1 point: lunar-orbit tilt.
• 1 point: season mechanism involving axial tilt and illumination.

Question 41 · 3 points

For one star, planet B has semimajor axis 9 times planet A's. Find the period ratio using T²∝a³ and explain why gravity does not cancel in a circular orbit.

Worked answer

27 times the period; net inward force is needed, not canceled by a real outward force in an inertial model.

Period ratio=√(9³)=27.

Gravity supplies inward acceleration that changes velocity direction.

Marking criteria

• 1 point: Kepler ratio setup.
• 1 point: ratio 27 and same-star condition.
• 1 point: inward acceleration/velocity-direction explanation.

Question 42 · 1 point

The Sun’s main energy source is…

1. coal combustion
2. nuclear fusion
3. reflected moonlight
4. friction with air

Worked answer

nuclear fusion

Hydrogen fusion supplies energy in its core.

1 point for the correct objective answer; no written-method marks for this item.

Question 43 · 1 point

Elements heavier than iron are formed mainly

1. in ordinary main-sequence fusion
2. in supernovae and similar extreme events
3. in planets
4. in comets

Worked answer

in supernovae and similar extreme events

Fusion beyond iron absorbs energy, so extreme conditions are required.

1 point for the correct objective answer; no written-method marks for this item.

Question 44 · 1 point

That more distant galaxies show greater redshift is evidence for

1. Earth at the centre
2. an expanding universe
3. a static universe
4. measurement error

Worked answer

an expanding universe

Every observer in a uniformly expanding space sees the same pattern.

1 point for the correct objective answer; no written-method marks for this item.

Question 45 · 3 points

A known spectral line at 600 nm appears at 612 nm. Calculate z and explain why several matching lines are useful.

Worked answer

z=0.02; multiple lines reduce ambiguous identification. This alone is not a complete cosmological history.

z=(612−600)/600=0.02.

A matched line pattern tests identification and shift consistency.

Marking criteria

• 1 point: redshift formula.
• 1 point: correct dimensionless value.
• 1 point: line-pattern evidence and stated limitation.

Question 46 · 3 points

A star is cooler than another but much more luminous. Explain what this suggests about size and why apparent brightness alone cannot settle the comparison.

Worked answer

The cool luminous star likely has a larger radiating surface; luminosity requires distance-aware evidence.

Lower surface temperature means lower emission per area in the model.

High total output needs greater emitting area; apparent brightness also depends on distance.

Marking criteria

• 1 point: luminosity versus apparent brightness.
• 1 point: surface-temperature/emitting-area reasoning.
• 1 point: role of distance or H–R diagram evidence.

Question 47 · 1 point

Which of these is a renewable resource?

1. Coal
2. Wind
3. Natural gas
4. Copper ore

Worked answer

Wind

Wind is continuously produced by uneven heating of Earth's atmosphere, so it's renewable on a human timescale.

1 point for the correct objective answer; no written-method marks for this item.

Question 48 · 1 point

A renewable resource can still be depleted if it is

1. used at all
2. used faster than it is replenished
3. stored
4. labelled renewable

Worked answer

used faster than it is replenished

Fish stocks and aquifers renew but can be exhausted by overuse.

1 point for the correct objective answer; no written-method marks for this item.

Question 49 · 1 point

The strongest evidence that a conservation measure worked is a recovery measured against

1. public opinion
2. a baseline and an untreated comparison site
3. the project's cost
4. the number of volunteers

Worked answer

a baseline and an untreated comparison site

Only a baseline and a control separate the measure's effect from background change.

1 point for the correct objective answer; no written-method marks for this item.

Question 50 · 3 points

A renewable forest gains 15 wood units yearly and loses 22 to harvest. Find stock change and explain why renewable does not mean unlimited.

Worked answer

The stock falls by 7 units/year despite ongoing regrowth.

Change=15−22=−7 units/year.

Replacement is slower than use in the supplied model.

Marking criteria

• 1 point: budget method.
• 1 point: −7 units/year.
• 1 point: timescale-based renewable/depletion explanation.

Question 51 · 3 points

Runoff design A reduces modeled flow from 200 to 150 mL; B reduces it to 120 mL. Compare percentages and recommend additional evidence before adopting B.

Worked answer

B reduces more runoff in this model, but adoption requires broader evidence and monitoring.

A reduction=50/200=25%; B=80/200=40%.

Compare costs, habitat, maintenance and scaling to real storms under equivalent conditions.

Marking criteria

• 1 point: both percentage reductions.
• 1 point: equivalent-condition model comparison.
• 1 point: at least two relevant additional criteria or limits.