This is a working draft for Leslie's review. The dependency edges below are a first pass — the diagram and the prerequisite table are the parts to check hardest, since they drive hold-vs-advance decisions.
The course map shows the eight units as a spine — minerals first, deep time last. But the real prerequisite structure isn't a straight line: it's a directed graph. Geology is more strictly cumulative than most subjects — igneous rock needs minerals, metamorphic rock closes the loop only after both igneous and sedimentary, and deep time can be read only once the layered record is in hand. A weak concept early doesn't just lower one grade, it cascades into everything downstream that needs it. This page is the map a guide uses to find the concept that's actually blocking a stuck student.
An arrow means “must be mastered first.” Units 04 and 07 each pull from two upstream units — those are the cascade points where one soft prerequisite quietly breaks several later units.
Prerequisite gating
A unit unlocks when its prerequisites are mastered — demonstrated, not merely seen. "Covered in class" is not the gate; a cleared rubric is. The difference matters most at the cascade points, where a soft prerequisite quietly breaks two or three later units.
| Unit | Must have mastered first |
|---|---|
| 01 Minerals | — (entry point) |
| 02 Igneous Rocks & Volcanism | 01 (igneous crystals grow from the same minerals) |
| 03 Sedimentary Rocks & Stratigraphy | 01 (sediment is broken-down mineral grains) |
| 04 Metamorphic Rocks & the Rock Cycle | 02 + 03 (recrystallizes igneous & sedimentary rock; closes the cycle) |
| 05 Plate Tectonics & Mountain Building | 04 (metamorphism is driven at plate boundaries) |
| 06 Earthquakes & Earth’s Interior | 05 (quakes release the stress built by plate motion) |
| 07 Weathering, Erosion & Landforms | 01 + 03 (minerals set weathering rate; feeds the sedimentary record) |
| 08 Geologic Time & Earth History | 03 (superposition — relative dating) + radiometric half-life math |
Gap-cascade diagnosis
When a student stalls late, the visible symptom is rarely the real problem — the broken concept is usually upstream. Trace the arrows backward. Common cascades:
| Late symptom | Upstream concept to check first |
|---|---|
| Metamorphic grade and the rock cycle won’t close (Unit 04) | Igneous and sedimentary rock from Units 02 and 03 — metamorphism reworks both. |
| Relative dating of a section comes out scrambled (Unit 08) | Superposition and stratigraphy from Unit 03 — not the dating method itself. |
| Mountain-building sequences don't add up (Unit 05) | The rock cycle from Unit 04 — metamorphism is what plate collisions drive. |
| Weathering and landform reasoning goes wrong (Unit 07) | Mineral properties from Unit 01 — hardness and solubility set the weathering rate. |
Using the graph to plan a re-attempt
The graph turns a "not yet" into a targeted re-attempt instead of a whole-unit re-teach. When a student fails a downstream demonstration:
- Trace backward to the upstream node the symptom points to.
- Re-attempt the upstream concept first — close the gap at its source, not where it surfaced.
- Then re-run the downstream demonstration. Often it passes without any re-teaching of the downstream unit at all, because the cascade is resolved.
This is also where the integration guide matters: some geology concepts depend on an applied-math idea — half-life arithmetic for radiometric dating, proportional reasoning for deposition and plate-motion rates — from another spoke. When the upstream geology node looks solid but the student still stalls, check the cross-disciplinary dependency before re-teaching the geology.