How is past climate reconstructed from the rock and fossil record?
The use of lithological and palaeontological proxies (evaporites, coals, tillites, coral reefs, fossil assemblages) and isotopic and geochemical methods to reconstruct past climates, and the role of palaeoclimate evidence in confirming continental movement.
A focused WJEC and Eduqas A-Level Geology G3 answer on how past climates are reconstructed from lithological proxies (evaporites, coals, tillites, reef limestones), fossil assemblages and oxygen-isotope and geochemical methods, and how palaeoclimate indicators found in unexpected latitudes provide evidence for continental drift.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
The climate half of G3 asks how the rock and fossil record is read for past climate. WJEC wants the standard lithological and palaeontological proxies, an awareness of isotopic and geochemical methods, and the powerful argument that palaeoclimate indicators in the wrong latitude are evidence for continental drift. It links back to plate tectonics (F4) and forward to Quaternary climate change (T3).
The answer
Lithological proxies
Certain rocks form only under particular climates, so they act as climate proxies:
Palaeontological and geochemical proxies
Fossil assemblages indicate climate because organisms are adapted to particular conditions (a tropical flora means warm and wet). Oxygen isotopes in fossil shells and ice are a key geochemical proxy: the ratio of oxygen-18 to oxygen-16 varies with temperature and with the volume of ice locked up on land, so isotope curves track past temperature and ice volume. Other geochemical signals (such as carbon isotopes) record changes in the carbon cycle.
Palaeoclimate as evidence for drift
Examples in context
The Permo-Carboniferous coals of Britain formed in tropical swamps when the region lay near the equator, while Permian and Triassic desert sandstones and evaporites above them record Britain drifting into the arid subtropics. Gondwanan tillites matched across India, Africa, South America, Antarctica and Australia were central to Wegener's case for continental drift. Deep-sea oxygen-isotope records from foraminifera underpin the modern timescale of Quaternary glacial and interglacial cycles.
Try this
Q1. State the climate indicated by evaporites, coal and tillite. [3 marks]
- Cue. Evaporites hot and arid; coal warm and wet (humid); tillite cold and glacial.
Q2. Explain how oxygen isotopes are used as a palaeoclimate proxy. [2 marks]
- Cue. The ratio of oxygen-18 to oxygen-16 in shells and ice varies with temperature and land-ice volume, so it tracks past temperature and ice.
Q3. Explain why glacial tillites now in warm latitudes are evidence for continental drift. [2 marks]
- Cue. Glacial deposits form in polar latitudes, so finding them in warm regions means the continent has drifted from a former polar position.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC Eduqas 20206 marksDescribe how different sedimentary rocks and fossils can be used as proxies to reconstruct the climate at the time of deposition.Show worked answer →
Take each proxy and say what climate it indicates, because the marks reward distinct, justified proxies.
Evaporites (rock salt, gypsum) form where evaporation exceeds water supply, so they indicate a hot, arid climate, typically in the subtropical desert belts.
Coal forms from abundant plant matter in waterlogged swamps, so it indicates a warm, wet, humid climate with high productivity.
Tillites (lithified glacial till) and striated, faceted clasts indicate cold, glacial conditions and the former presence of ice.
Coral reef limestones indicate warm, shallow, clear tropical seas, and desert sandstones with large-scale dune cross-bedding indicate hot, dry conditions.
Fossils add to this: particular plants and animals are adapted to particular climates, so a tropical fossil flora indicates a warm, wet climate.
So each rock or fossil acts as a climate proxy, and together they reconstruct the conditions at the time of deposition.
Markers reward evaporites for hot and arid, coal for warm and wet, tillites for cold and glacial, and reef limestone for warm tropical seas, each correctly justified.
WJEC Eduqas 20215 marksExplain how palaeoclimate indicators found at unexpected latitudes provide evidence for continental drift.Show worked answer →
Link the climate proxy to the latitude it implies, then to plate movement, because that is the chain of reasoning.
Climate-sensitive rocks form only in particular climate belts, which are tied to latitude: evaporites and desert sandstones form in the hot, dry subtropics, coals in the warm, wet tropics and temperate zones, and tillites in cold polar regions.
When such rocks are found far from the latitude their climate implies, for example glacial tillites of similar age in India, Africa, South America and Australia (now in warm latitudes), the simplest explanation is that those landmasses lay in polar latitudes when the rocks formed and have since drifted.
The matching of these deposits across now-separated continents (and their fit when reassembled as Gondwana) is strong evidence that the continents were once joined and have moved, supporting continental drift and plate tectonics.
Markers reward climate proxies indicating a former latitude, the mismatch with present latitude implying movement, and the cross-continental match of glacial deposits as evidence for drift.
Related dot points
- The evidence for organic evolution from the fossil record (morphological change through time, transitional forms), the major patterns of the history of life, and the causes and consequences of mass extinctions, including the end-Permian and end-Cretaceous events.
A focused WJEC and Eduqas A-Level Geology G3 answer on the fossil evidence for organic evolution (morphological change through time and transitional forms), the broad history of life from the first cells to mammals, and the causes and effects of mass extinctions, focusing on the end-Permian and the end-Cretaceous events.
- The use of functional morphology to interpret the mode of life of fossil organisms (feeding, locomotion, environment), the concept of trace fossils and their value, and the use of fossil assemblages and adaptations to reconstruct past environments.
A focused WJEC and Eduqas A-Level Geology G3 answer on functional morphology, how the shape and structure of a fossil reveal its feeding, locomotion and environment, the value of trace fossils, and how fossil assemblages and adaptations are used to reconstruct ancient environments and ecological relationships.
- The development of plate tectonic theory from continental drift, and the evidence for it (continental fit, matching geology and fossils, palaeoclimate, sea-floor spreading and palaeomagnetic stripes).
A focused answer to WJEC and Eduqas A-Level Geology F4 on plate tectonic theory, covering the development from continental drift, and the evidence (continental fit, matching geology and fossils, palaeoclimate, sea-floor spreading and the symmetry of palaeomagnetic stripes) that confirmed it.
- Quaternary geology (option T3): the evidence for glacial and interglacial cycles, glacial and periglacial processes and deposits, the dating of Quaternary events, and the causes of Quaternary climate change including Milankovitch cycles.
A focused WJEC and Eduqas A-Level Geology answer on the optional theme T3 Quaternary geology, covering the evidence for glacial and interglacial cycles, glacial and periglacial processes and deposits, the dating of Quaternary events, and the causes of Quaternary climate change including Milankovitch orbital cycles.
- Deposition in different environments, the formation of sedimentary structures (bedding, cross-bedding, graded bedding, ripple marks) and how these are used as way-up indicators and palaeoenvironment evidence.
A focused answer to WJEC and Eduqas A-Level Geology F2 on deposition, covering depositional environments and the sedimentary structures (bedding, cross-bedding, graded bedding, ripple marks, desiccation cracks) used as way-up indicators and to reconstruct ancient palaeoenvironments.
Sources & how we know this
- WJEC Eduqas A-level Geology specification — WJEC Eduqas (2017)