What does the Quaternary record reveal about ice ages and rapid climate change?
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.
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What this dot point is asking
T3 is one of the three optional Geological Themes; learners study one of T3, T4 and T5. This overview covers the Quaternary option: the evidence for glacial and interglacial cycles, glacial and periglacial processes and deposits, the dating methods, and the causes of Quaternary climate change, especially Milankovitch cycles. It applies palaeoclimate ideas (G3) to the most recent geological period.
The answer
The Quaternary and its cycles
The Quaternary (the last roughly 2.6 million years) is marked by repeated glacial (cold, ice advance) and interglacial (warm, ice retreat) cycles. We currently live in an interglacial.
Evidence for the cycles
Glacial and periglacial processes
Glaciers erode by abrasion (rock-armoured ice grinding the bed) and plucking (freezing onto and tearing out rock), and deposit unsorted till and sorted outwash. Periglacial processes include frost shattering and solifluction (downslope flow of saturated, thawed soil over frozen ground).
Dating the Quaternary
Quaternary events are dated by radiocarbon (carbon-14, useful to about 50,000 years), other methods such as luminescence and uranium-series, the correlation of oxygen-isotope stages, and varve (annual layer) counting.
Causes: Milankovitch cycles
Examples in context
British glacial deposits across the Midlands, East Anglia and the north record successive Quaternary glaciations, with erratics traced to distant source rocks. Deep-sea oxygen-isotope records define the marine isotope stages used to correlate Quaternary events worldwide. Ice cores from Greenland and Antarctica show the tight link between temperature and carbon dioxide through the recent glacial cycles, central to understanding climate change.
Try this
Q1. Distinguish till from outwash. [2 marks]
- Cue. Till is unsorted material deposited directly by ice; outwash is sorted material deposited by meltwater.
Q2. Name the three Milankovitch cycles and their approximate periods. [3 marks]
- Cue. Eccentricity (about 100,000 years), obliquity (about 41,000 years), precession (about 21,000 years).
Q3. Explain how cool northern summers lead to the growth of ice sheets. [2 marks]
- Cue. When summers are cool, winter snow does not fully melt, so it accumulates year on year and ice sheets grow.
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 the evidence used to reconstruct the glacial and interglacial cycles of the Quaternary.Show worked answer →
Set out the lines of evidence and what each shows, because the marks reward distinct, justified evidence.
Glacial deposits and landforms: tills (boulder clay), moraines, erratics, striated and faceted clasts and U-shaped valleys record former ice cover and its extent, while periglacial features such as ice-wedge casts record cold, non-glaciated ground.
Ocean-sediment oxygen isotopes: the oxygen-18 to oxygen-16 ratio in foraminifera shells in deep-sea cores varies with ice volume, giving a continuous record of many glacial and interglacial cycles.
Ice cores: layers of polar ice preserve trapped air bubbles and isotopes that record past temperature and atmospheric carbon dioxide.
Pollen and fossils: changing pollen assemblages and cold or warm-adapted fauna in lake and bog sediments record the swings between cold (glacial) and warm (interglacial) conditions.
Together these terrestrial, marine and ice records reconstruct the repeated glacial-interglacial cycles of the Quaternary.
Markers reward glacial deposits and landforms, oxygen-isotope records from ocean cores or ice, and pollen or faunal evidence, each linked to reconstructing the cycles.
WJEC Eduqas 20225 marksExplain the role of Milankovitch cycles in causing the glacial and interglacial cycles of the Quaternary.Show worked answer →
Explain the orbital variations and how they change the climate, because that is the mechanism asked for.
Milankovitch cycles are regular changes in the Earth's orbit and axis that alter the amount and distribution of solar radiation reaching the Earth. There are three: eccentricity (the shape of the orbit, on a roughly 100,000 year cycle), obliquity (the tilt of the axis, about 41,000 years) and precession (the wobble of the axis, about 21,000 years).
These variations change how much sunlight high northern latitudes receive in summer. When summers are cool, winter snow does not fully melt and ice sheets grow (a glacial); when summers are warmer, ice melts back (an interglacial).
The orbital pacing matches the timing of the glacial-interglacial cycles seen in the oxygen-isotope record, and the effect is amplified by feedbacks such as changing ice albedo and carbon dioxide, so Milankovitch cycles are regarded as the pacemaker of the ice ages.
Markers reward the three orbital cycles (eccentricity, obliquity, precession) changing solar input, the link of cool summers to ice growth, and the match with the isotope record amplified by feedbacks.
Related dot points
- Geological evolution of Britain (option T4): the main tectonic events and orogenies (Caledonian, Variscan, Alpine), the changing palaeogeography and palaeolatitude of Britain through the Phanerozoic, and the rocks and structures these events produced.
A focused WJEC and Eduqas A-Level Geology answer on the optional theme T4 geological evolution of Britain, covering the main orogenies (Caledonian, Variscan, Alpine), the changing palaeogeography and palaeolatitude of Britain through the Phanerozoic, and the characteristic rocks and structures each event produced.
- Geology of the lithosphere (option T5): the lithosphere and asthenosphere, the structure and formation of oceanic and continental crust, the geophysical evidence for the Earth's interior (seismic, gravity, magnetic, heat flow), and the processes of isostasy and crustal recycling.
A focused WJEC and Eduqas A-Level Geology answer on the optional theme T5 geology of the lithosphere, covering the lithosphere and asthenosphere, the structure and formation of oceanic and continental crust, the geophysical evidence for the Earth's interior, and isostasy and crustal recycling.
- 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.
- The principle of radiometric dating using radioactive decay and half-life, the parent-to-daughter ratio, the choice of isotope system, and the assumptions and limitations of the method.
A focused answer to WJEC and Eduqas A-Level Geology F3 on absolute dating, covering radioactive decay and half-life, calculating an age from the parent-to-daughter ratio, the choice of isotope system (uranium-lead, potassium-argon, carbon-14), and the assumptions and limitations of radiometric dating.
- The mechanisms of physical and chemical weathering, the distinction between weathering, erosion and transport, and how transport agents round and sort sediment to record transport history.
A focused answer to WJEC and Eduqas A-Level Geology F2 on surface processes, covering physical and chemical weathering mechanisms, the difference between weathering, erosion and transport, and how rounding and sorting of sediment by water, wind and ice record transport distance and energy.
Sources & how we know this
- WJEC Eduqas A-level Geology specification — WJEC Eduqas (2017)