← Geology syllabus

EnglandGeology

Module 2 and 4: Fossils and time; Interpreting the past

5 dot points across 5 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

What does the fossil record tell us about evolution and mass extinctions?

Evolution and the fossil record: evidence for evolution from the fossil record (morphological change through time, transitional forms, adaptive radiation); the models of evolutionary change (gradualism versus punctuated equilibrium); mass extinctions and their causes and effects (for example the end-Permian and end-Cretaceous events); the incompleteness and biases of the fossil record.
A focused answer to the OCR H414 dot point on evolution. Covers the fossil evidence for evolution (morphological change, transitional forms, adaptive radiation), the gradualism and punctuated equilibrium models, mass extinctions (the end-Permian and end-Cretaceous events) and their causes and effects, and the incompleteness and biases of the fossil record.
12 min answer →

How are fossils preserved, and what makes a fossil useful for dating rocks?

Fossils: the conditions that favour preservation (rapid burial, anoxia, hard parts, fine sediment); the modes of preservation (moulds and casts, permineralisation, carbonisation, and preservation in amber or ice); the properties of a good index (zone) fossil (abundant, widespread, easily recognised, short stratigraphic range); the distinction between body and trace fossils.
A focused answer to the OCR H414 dot point on fossils. Covers the conditions favouring preservation, the modes of preservation (moulds and casts, permineralisation, carbonisation, amber and ice), the properties of a good index or zone fossil, and the distinction between body and trace fossils.
12 min answer →

How do we measure the absolute age of a rock using radioactive decay?

Radiometric dating: radioactive decay of unstable parent isotopes to stable daughter isotopes; the concept of half-life as a constant; the use of parent-to-daughter ratios to calculate absolute ages; the main isotopic systems (uranium-lead, potassium-argon and carbon-14) and their suitable age ranges; the assumptions and limitations of radiometric dating; the combination of absolute and relative dating.
A focused answer to the OCR H414 dot point on radiometric dating. Covers radioactive decay of parent to daughter isotopes, half-life as a constant, calculating absolute ages from parent-to-daughter ratios, the uranium-lead, potassium-argon and carbon-14 systems and their ranges, the assumptions and limitations, and combining absolute with relative dating.
14 min answer →

How do we work out the order of geological events without knowing absolute ages?

Relative dating: the principles used to order geological events (superposition, original horizontality, cross-cutting relationships, included fragments and faunal succession); the recognition of way-up evidence; the application of these principles to construct the geological history of a cross-section, including faults, intrusions and unconformities.
A focused answer to the OCR H414 dot point on relative dating. Covers superposition, original horizontality, cross-cutting relationships, included fragments and faunal succession, way-up evidence, and how to apply these principles to reconstruct the geological history of a cross-section with faults, intrusions and unconformities.
13 min answer →

How is geological time divided, and how do we correlate rocks between distant areas?

The geological record: the hierarchy of the geological time scale (eon, era, period, epoch) and the major divisions (Precambrian and the Phanerozoic eras); correlation of strata by lithostratigraphy (matching rock units) and biostratigraphy (matching fossils and biozones); the use of marker horizons such as volcanic ash bands; the distinction between rock units (systems) and time units (periods).
A focused answer to the OCR H414 dot point on the geological time scale and correlation. Covers the eon, era, period and epoch hierarchy and the major divisions, correlation by lithostratigraphy and biostratigraphy, the use of marker horizons such as ash bands, and the distinction between rock units and time units.
12 min answer →