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 — the solid Earth first, astronomy last. But the real prerequisite structure isn't a straight line: it's a directed graph. Earth science is more cumulative than it looks — minerals & rocks need plate tectonics, weathering needs the rock cycle, climate needs both the atmosphere and the weathering-driven carbon cycle. 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 05, 06, and 08 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 Earth's Structure & Plate Tectonics | — (entry point) |
| 02 Minerals & Rocks | 01 (rocks & minerals form in tectonic and rock-cycle settings) |
| 03 Weathering, Erosion & Soil | 02 (weathering acts on rock & minerals; soil is weathered rock) |
| 04 Earth's History & Geologic Time | 02 (rock strata & fossils are the record of time) |
| 05 The Atmosphere & Weather | 03 (surface & carbon exchange) + 04 (the atmosphere evolved over geologic time) |
| 06 Climate & Climate Change | 03 (weathering & the carbon cycle) + 05 (climate is long-term weather) |
| 07 The Hydrosphere | 05 (the water cycle couples air & ocean) |
| 08 Astronomy & Earth in Space | 06 (the Sun's control of climate) + 07 (the Moon's control of the tides) |
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 |
|---|---|
| Seasons and tides won't connect to Earth–Moon–Sun (Unit 08) | Climate and the hydrosphere from Units 06 & 07 — you can't tie the Sun to climate or the Moon to tides the student doesn't yet own. |
| The water cycle won't close (Unit 07) | The atmosphere & weather from Unit 05 — evaporation and precipitation are atmospheric before they reach the ocean. |
| Climate feedbacks don't hold together (Unit 06) | The atmosphere from Unit 05 — climate is long-term weather, so shaky weather makes climate collapse. |
| The atmosphere and weather don't cohere (Unit 05) | Weathering and Earth's history from Units 03 & 04 — the atmosphere sits on the weathered surface and is a product of geologic time. |
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 earth science concepts depend on an applied-math idea — logarithms for the Richter magnitude scale, ratio and scale for reading a map — from another spoke. When the upstream earth science node looks solid but the student still stalls, check the cross-disciplinary dependency before re-teaching the earth science.