Active learning ideas
Stratigraphy is the science of reading Earth's history through its layers. This topic introduces the fundamental 'laws' of geology established by Nicolas Steno and others, including superposition, original horizontality, and cross-cutting relationships. For Year 12 students, this is the first step in moving from a static view of rocks to a chronological narrative of geological events. It aligns with the Eduqas AS/A-level focus on relative dating and stratigraphic principles.
Activity 01
Groups are given complex geological cross-sections featuring folds, faults, intrusions, and unconformities. They must work together to list the events in chronological order, citing the specific stratigraphic law that justifies each step.
How is the principle of superposition used to date rocks?
Activity 02
Using layers of coloured sand or play-dough, students model the four stages of an angular unconformity: deposition, tilting, erosion, and renewed deposition. They then 'slice' their model to see how it appears in a cross-section.
What does an unconformity represent in geological time?
Activity 03
Students look at a photo of a dyke cutting through a series of sedimentary layers. They must decide which is older and why, then compare their reasoning with a partner before presenting the 'Law of Cross-Cutting Relationships' to the class.
How do cross-cutting relationships help establish relative age?
A few notes on teaching this unit
Watch Out for These Misconceptions
The oldest rock is always at the bottom.
While generally true (superposition), tectonic activity can overturn sequences. Students must look for 'way-up' indicators like graded bedding or fossils. A 'detective' activity where students find evidence of overturning helps correct this oversimplification.
An unconformity is just a line on a map.
An unconformity represents a vast span of time and a significant geological event (like uplift and erosion). Using a 'missing pages in a book' analogy helps students appreciate the temporal scale involved.
Methods used in this brief
The Fossil Record and Evolution
Study the modes of fossil preservation and the morphological features of major fossil groups such as trilobites, ammonites, and graptolites. Evaluate how fossils provide evidence for evolutionary change and mass extinctions.
8 methodologies
Dating Methods in Geology
Examine absolute dating techniques, focusing on radiometric dating using isotopes like Potassium-Argon and Rubidium-Strontium. Calculate the ages of rocks using half-life principles.
8 methodologies