What does G3 of WJEC A-Level Geology cover?

G3, Past Life and Past Climates, is the third topic of the A2 section Interpreting the Geological Record. It covers the fossil evidence for organic evolution and the broad history of life, the causes and consequences of mass extinctions (especially the end-Permian and end-Cretaceous), the use of functional morphology and trace fossils to deduce the mode of life and environment of fossil organisms, and the lithological, palaeontological and isotopic proxies used to reconstruct past climates and to support continental drift.

What fossil evidence supports evolution?

Three main lines. Morphological change through time, where lineages traced up the column change form gradually, as in the horse lineage increasing in size and reducing its toes. Transitional forms with mixed features, such as Archaeopteryx, which has feathers and wings but also teeth, claws and a bony tail, bridging reptiles and birds. And a consistent worldwide order of appearance, with simpler groups appearing before more complex ones in the same sequence everywhere.

What caused the end-Permian and end-Cretaceous extinctions?

The end-Permian extinction (about 252 million years ago), the largest, removing about 90 percent of marine species, is linked to vast Siberian Traps volcanism causing global warming, ocean anoxia and acidification. The end-Cretaceous extinction (about 66 million years ago), which removed the non-avian dinosaurs and the ammonites, is linked to the Chicxulub meteorite impact, evidenced by a global iridium-rich clay, shocked quartz and tektites, with Deccan volcanism as a contributing stress.

How is functional morphology used?

Functional morphology interprets the function of an organism's structures from their form to deduce how it fed, moved and lived. For example, a thin, streamlined bivalve shell with a deep pallial sinus (marking long siphons) indicates a burrowing life, while a thick, ornamented shell without a deep sinus, often attached or cemented, indicates a fixed or surface life. Each feature is read as an adaptation to a particular way of life.

How is past climate reconstructed?

From proxies. Lithological proxies include evaporites (hot, arid), coal (warm, wet), tillite (cold, glacial), reef limestone (warm tropical seas) and desert sandstone (hot, dry). Fossil assemblages indicate climate through adaptation, and oxygen isotopes in shells and ice record temperature and ice volume. Because these rocks form in latitude-controlled belts, finding them at the wrong latitude, such as Gondwanan glacial tillites now in warm regions, is evidence that continents have drifted.

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WJEC A-Level Geology G3 Past Life and Past Climates: a deep dive on evolution, palaeoecology and palaeoclimate

A deep-dive WJEC and Eduqas A-Level Geology guide to G3, Past Life and Past Climates. Covers the fossil evidence for evolution and the major mass extinctions, the use of functional morphology and trace fossils to read mode of life and environment, and the lithological, palaeontological and isotopic proxies used to reconstruct past climate and confirm drift, with exam-style worked questions.

Generated by Claude Opus 4.814 min readWJECUpdated 2026-06-16

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What G3 actually demands
Evolution and extinction
Palaeoecology
Palaeoclimate
Check your knowledge

What G3 actually demands

G3 turns fossils and climate-sensitive rocks into evidence. Examiners want interpretation, not lists: the fossil record as testable evidence for evolution, the causes and biological consequences of extinctions, the deduction of mode of life and environment from morphology and traces, and the reconstruction of climate from proxies. The recurring higher-order skill is reading a sequence or an assemblage and explaining what it records.

Each part of the topic has a dot-point page with worked questions; this overview connects them.

Evolution and extinction

The fossil record supports evolution through morphological change traced up the column, transitional forms such as Archaeopteryx, and a consistent order of appearance. Mass extinctions reset the system: the end-Permian (Siberian Traps, about 90 percent of marine species) was the largest, and the end-Cretaceous (Chicxulub impact, with iridium and shocked quartz) removed the dinosaurs and ammonites and let mammals radiate.

Palaeoecology

Functional morphology reads structures as adaptations, so a thin shell with a deep pallial sinus marks a burrower and a thick ornamented shell marks a protected or fixed life. Trace fossils are valued because they are preserved in place and so record the true environment. Assemblages combined with sedimentary structures reconstruct settings such as warm, shallow reef seas.

Palaeoclimate

Evaporites, coal, tillite, reef limestone and desert sandstone act as climate proxies, fossils add climatic adaptation, and oxygen isotopes record temperature and ice volume. Climate proxies at the wrong latitude are strong evidence for continental drift, tying G3 back to plate tectonics.

Check your knowledge

Attempt these under timed conditions, then check against the solutions.

Name a transitional fossil and the groups it links. (2 marks)
State the cause of the end-Permian extinction and one effect. (2 marks)
State two pieces of evidence for the end-Cretaceous impact. (2 marks)
Explain what a deep pallial sinus indicates about a bivalve. (2 marks)
Give two reasons trace fossils are good environmental indicators. (2 marks)
State the climate indicated by evaporites, coal and tillite. (3 marks)

Sources & how we know this

WJEC Eduqas A-level Geology specification — WJEC Eduqas (2017)