Eduqas A-level Geology · G3

Past life and past climates

Exam-style questions with answers for G3 Past life and past climates in Eduqas A-level Geology (spec A480QS). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

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Question 1 · Spec G3, Key Idea 1 · Early life
Explain why evidence for very early life is difficult to interpret. [2 marks]
Answer:
Very old rocks are rare and usually altered or metamorphosed (1); and possible fossils or chemical signals may have non-biological origins or be contaminated (1).
Question 2 · Spec G3, Key Idea 1 · Ediacaran fauna
State the significance of the Ediacaran fauna. [2 marks]
Answer:
It is the earliest diverse assemblage of multicellular animals (1); made of soft-bodied organisms, before the Cambrian explosion (1).
Question 3 · Spec G3, Key Idea 1 · Cambrian explosion
Describe the changes associated with the Cambrian explosion. [2 marks]
Answer:
A rapid increase in the diversity and complexity of marine animals (1); and the evolution of hard, mineralised skeletons, so the fossil record became much richer (1).
Question 4 · Spec G3, Key Idea 1 · Diversity
Explain why a sudden rise in fossil diversity may not be a sudden evolutionary event. [2 marks]
Answer:
The evolution of hard parts improves preservation (1); and differences in sampling and exposure can make diversity appear to rise suddenly (1).
Question 5 · Spec G3, Key Idea 1 · Diversity curves
State what Sepkoski's diversity curves show. [2 marks]
Answer:
Changes in the diversity of marine families through time (1); showing radiations and mass extinctions of the Cambrian, Palaeozoic and modern faunas (1).
Question 6 · Spec G3, Key Idea 1 · Diversity curves
A diversity curve falls sharply then recovers slowly. Suggest what this shows. [2 marks]
Answer:
A mass extinction (1); followed by slow recovery and adaptive radiation (1).
Question 7 · Spec G3, Key Idea 1 · Colonisation of land
State three problems organisms had to overcome to live on land. [3 marks]
Answer:
Any three from: water loss (desiccation) (1); support against gravity (1); gas exchange in air (1); reproduction away from water (1).
Question 8 · Spec G3, Key Idea 1 · Colonisation of land
Explain how plant fossils show the spread of life onto land. [2 marks]
Answer:
Their first appearance and spread through the rock record shows when land was colonised (1); roots in growth position show plants grew in that place (1).
Question 9 · Spec G3, Key Idea 1 · Vertebrates on land
State fossil evidence that a vertebrate could move on land. [2 marks]
Answer:
Strong limbs with digits rather than fins (1); and strong limb girdles to support the body (1).
Question 10 · Spec G3, Key Idea 1 · Functional morphology
Explain why one feature alone can give an uncertain interpretation of a fossil animal's lifestyle. [2 marks]
Answer:
One feature may have several possible functions (1); so the whole anatomy and the sediment it was found in should be considered (1).
Question 11 · Spec G3, Key Idea 1 · Evolutionary trees
State what a branching point on an evolutionary tree represents. [1 mark]
Answer:
A common ancestor, where lineages diverged.
Question 12 · Spec G3, Key Idea 1 · Evolution
Describe gradualism. [1 mark]
Answer:
Evolution happens through slow, continuous small changes over long periods of time.
Question 13 · Spec G3, Key Idea 1 · Evolution
Describe punctuated equilibrium. [2 marks]
Answer:
Long periods with little evolutionary change (stasis) (1); interrupted by short periods of rapid change, often when new species form (1).
Question 14 · Spec G3, Key Idea 1 · Evolution
Explain why an incomplete fossil record makes it hard to tell gradualism from punctuated equilibrium. [2 marks]
Answer:
Gaps in the record may hide gradual transitions (1); making change appear sudden when it was not (1).
Question 15 · Spec G3, Key Idea 1 · Extinction
Distinguish between mass extinction and background extinction. [2 marks]
Answer:
Background extinction is the normal, continuous low rate of species loss (1); a mass extinction is the loss of a large proportion of species across many groups in a geologically short time (1).
Question 16 · Spec G3, Key Idea 1 · End-Permian extinction
Explain why the end-Permian extinction may have had several causes. [2 marks]
Answer:
Siberian Traps volcanism released gases that changed the climate (1); this led to ocean acidification and anoxia, which together stressed life (1).
Question 17 · Spec G3, Key Idea 1 · Flood basalts
State three ways large-scale basaltic volcanism affects the global environment. [3 marks]
Answer:
Any three from: CO₂ release causes global warming (1); SO₂ causes cooling and acid rain (1); ocean acidification (1); ocean anoxia (1).
Question 18 · Spec G3, Key Idea 1 · K-Pg extinction
State two pieces of evidence for an asteroid impact at the K-Pg boundary. [2 marks]
Answer:
Any two from: an iridium anomaly in the boundary clay (1); shocked quartz (1); tektites (glass spherules) (1); the Chicxulub crater (1).
Question 19 · Spec G3, Key Idea 1 · K-Pg extinction
Explain how an asteroid impact could cause extinctions worldwide. [2 marks]
Answer:
Dust and aerosols blocked sunlight (1); stopping photosynthesis and causing food chains to collapse (1).
Question 20 · Spec G3, Key Idea 1 · Extinction
Explain why the timing of an environmental event must match an extinction. [2 marks]
Answer:
A cause must happen just before or at the time of the extinction (1); accurate dating helps show a link rather than a coincidence (1).
Question 21 · Spec G3, Key Idea 1 · Extinction
Explain how a rapid fall in sea level could cause extinctions of shallow marine organisms. [2 marks]
Answer:
Continental shelves are exposed (1); so shallow marine habitats are lost (1).
Question 22 · Spec G3, Key Idea 1 · Calculations
Diversity falls from 240 taxa to 60. Calculate the percentage decline. [2 marks]
Answer:
Loss = 180 taxa (1); 180 ÷ 240 × 100 = 75% (1).
Question 23 · Spec G3, Key Idea 1 · Recovery
Explain why diversity may stay low for millions of years after an extinction. [2 marks]
Answer:
Ecosystems and food webs take time to rebuild (1); and new species take time to evolve from the few survivors (1).
Question 24 · Spec G3, Key Idea 2 · Wilson cycle
Explain how the Wilson cycle affects global climate and sea level. [2 marks]
Answer:
Opening and closing of oceans changes the arrangement of continents and ocean currents (1); and changes in mid-ocean ridge volume alter sea level (1).
Question 25 · Spec G3, Key Idea 2 · Continental position
Explain how the position of continents affects global climate. [2 marks]
Answer:
Continents redirect ocean currents (1); which changes how heat is transferred from the equator to the poles (1).
Question 26 · Spec G3, Key Idea 2 · Uplift
Explain how mountain uplift can cool the climate over long timescales. [2 marks]
Answer:
Uplift exposes fresh rock to chemical weathering (1); which removes CO₂ from the atmosphere (1).
Question 27 · Spec G3, Key Idea 2 · Volcanism
Explain how volcanoes can cause greenhouse warming. [1 mark]
Answer:
They release CO₂ from the Earth's interior into the atmosphere.
Question 28 · Spec G3, Key Idea 2 · Carbon cycle
Explain how silicate weathering acts as a long-term carbon sink. [2 marks]
Answer:
CO₂ dissolved in rainwater reacts with silicate minerals during weathering (1); the dissolved products are carried to the oceans and locked away in carbonate sediments (1).
Question 29 · Spec G3, Key Idea 2 · Feedbacks
Explain how methane hydrates can cause a positive feedback. [2 marks]
Answer:
Warming destabilises methane hydrates in sediments, releasing methane (1); methane is a greenhouse gas, so it causes more warming and more release (1).
Question 30 · Spec G3, Key Idea 2 · Feedbacks
Distinguish between a climate forcing and a positive feedback. [2 marks]
Answer:
A forcing starts a climate change, e.g. an increase in CO₂ (1); a positive feedback is a response that amplifies the change (1).
Question 31 · Spec G3, Key Idea 2 · Calculations
Temperature rises by 4 °C over 20 000 years. Calculate the mean rate per thousand years. [1 mark]
Answer:
4 ÷ 20 = 0.2 °C per thousand years.
Question 32 · Spec G3, Key Idea 2 · Data comparison
Explain why climate records should be compared at similar time resolution. [2 marks]
Answer:
Records averaged over long periods smooth out short, rapid changes (1); so comparing them with high-resolution modern data can be misleading (1).
Question 33 · Spec G3, Key Idea 3 · Proxies
Define the term 'palaeoclimate proxy'. [1 mark]
Answer:
A measurable feature that indirectly records past climate, such as fossils, sediments or isotope ratios.
Question 34 · Spec G3, Key Idea 3 · Proxies
Explain how reef-building coral fossils indicate past climate. [2 marks]
Answer:
Modern reef corals live in warm (above 18 °C), clear, shallow seas (1); so fossil reefs suggest similar conditions in the past (1).
Question 35 · Spec G3, Key Idea 3 · Proxies
Explain how fossil leaves can be used to estimate past climate. [2 marks]
Answer:
Leaf size and shape are related to climate in modern plants (1); e.g. smooth-edged leaves are more common in warm climates (1).
Question 36 · Spec G3, Key Idea 3 · Glacial evidence
State three pieces of sedimentary evidence for a glacial climate. [3 marks]
Answer:
Any three from: tillites (diamictites) (1); striated pavements (1); dropstones in marine sediments (1); varves (1).
Question 37 · Spec G3, Key Idea 3 · Climate zones
Explain why coal and tropical carbonates can form during an icehouse period. [2 marks]
Answer:
Climate varies with latitude (1); so warm equatorial areas can exist at the same time as polar ice sheets (1).
Question 38 · Spec G3, Key Idea 3 · Greenhouse periods
Explain how Cretaceous chalk supports a greenhouse climate. [2 marks]
Answer:
Chalk was deposited across very large areas of flooded continents (1); showing high sea levels with no large ice sheets (1).
Question 39 · Spec G3, Key Idea 3 · Anthropocene
State three pieces of evidence proposed for human influence on the geological record. [3 marks]
Answer:
Any three from: plastics and concrete (1); radionuclides from nuclear tests (1); fly ash from combustion (1); rapid changes in species distributions (1).
Question 40 · Spec G3, Key Idea 3 · Anthropocene
State the current status of the Anthropocene in the geological timescale. [1 mark]
Answer:
It is not a formal epoch; the proposal was rejected in 2024, but the term is still used informally.
Question 41 · Spec G3, Key Idea 3 · Time boundaries
Explain why a global, near-synchronous marker is needed to define a time boundary. [2 marks]
Answer:
It can be recognised and correlated in rocks around the world (1); local or diachronous signals cannot define a single global boundary (1).
Question 42 · Spec G3, Key Idea 3 · Oxygen isotopes
Name the ratio used in oxygen isotope studies. [1 mark]
Answer:
¹⁸O to ¹⁶O (expressed as δ¹⁸O).
Question 43 · Spec G3, Key Idea 3 · Oxygen isotopes
State how colder water affects the oxygen isotope ratio of carbonate shells. [1 mark]
Answer:
Shells formed in colder water have higher δ¹⁸O (more ¹⁸O).
Question 44 · Spec G3, Key Idea 3 · Oxygen isotopes
Explain why large ice sheets increase δ¹⁸O in seawater. [2 marks]
Answer:
Water containing light ¹⁶O evaporates more easily and is stored in ice sheets (1); leaving the oceans relatively enriched in ¹⁸O (1).
Question 45 · Spec G3, Key Idea 3 · Oxygen isotopes
Explain why a δ¹⁸O curve is not a pure temperature record. [2 marks]
Answer:
δ¹⁸O is affected by water temperature (1); and also by the volume of ice stored on land (1).
Question 46 · Spec G3, Key Idea 3 · Snowball Earth
Describe the Snowball Earth hypothesis. [1 mark]
Answer:
That the Earth was completely or almost completely covered in ice during the Neoproterozoic.
Question 47 · Spec G3, Key Idea 3 · Snowball Earth
Explain why low-latitude glacial deposits support Snowball Earth. [2 marks]
Answer:
Palaeomagnetism shows the deposits formed near the equator (1); so ice must have extended to the tropics (1).
Question 48 · Spec G3, Key Idea 3 · Snowball Earth
Explain why a diamictite alone does not prove glaciation. [2 marks]
Answer:
Poorly sorted deposits can also form by debris flows or landslides (1); so other evidence, such as striations and dropstones, is needed (1).
Question 49 · Spec G3, Key Idea 3 · Evidence
Explain why agreement between fossils, sediments and isotopes strengthens a climate interpretation. [2 marks]
Answer:
They are independent lines of evidence based on different assumptions (1); so agreement makes it unlikely that a local or preservation effect explains the result (1).
Question 50 · Spec G3, Key Idea 3 · Evaluation
State three things a good evaluation of an extinction hypothesis should consider. [3 marks]
Answer:
Any three from: timing (1); mechanism (1); alternative explanations (1); uncertainties and conflicting evidence (1).

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