# Session 7 — Inside the Planet: What We Know, What We Don't

<span class="ess-badge ess-b-amber">Format C — Relevance Map</span>
<span class="ess-badge ess-b-blue">Week 7</span>
<span class="ess-badge ess-b-coral">Relevance: Cascades volcanism · Sea level · Geothermal</span>

*PREM and its limits · Cascades volcanism · Glacial isostatic adjustment*

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```{dropdown} Hook (0 – 7 min)
Show the PREM velocity profile alongside a seismic tomography image of mantle plumes under Yellowstone. Ask:

**"PREM is a 1D model. This tomography image is 3D. What does the difference tell you — and what could you never learn from PREM alone?"**

Let students argue the contrast for 3 minutes before moving on.
```

```{dropdown} Discussion (7 – 42 min)
Three groups, three problems. 12 minutes of group work, then 3-minute reasoning presentations.

**Group A — Cascade volcanoes:**
Why do the Cascades have volcanoes? What does earth interior structure tell you about where the magma comes from, and what method would you use to image the subducting slab?

**Group B — Glacial isostatic adjustment and sea level:**
Sea level projections depend on how Earth's mantle responds to ice sheet melting (glacial isostatic adjustment). How does seismology connect to sea level science? What Earth interior properties matter?

**Group C — Geothermal prospecting:**
A geothermal company wants to know if there is a heat source at depth in a new area. How does PREM constrain where they should look?

After each presentation: *"What assumption in your reasoning would most change your answer if it were wrong?"*
```

```{dropdown} Relevance
**Basic science:** Everything we know about the Earth's liquid outer core, solid inner core, and 660-km phase transition came from seismology alone — no drill reaches any of it.

**Climate:** Glacial isostatic adjustment (GIA) — how the solid Earth rebounds after ice melts — is embedded in every IPCC sea level projection. The earth interior physics from this week affects where coastlines will be in 2100.

**Energy:** Geothermal energy development in the western US depends on seismic imaging of magmatic systems and heat flow models grounded in earth interior knowledge.
```

```{dropdown} Go Deeper
IRIS "EarthScope and the Dynamic Planet" resources · Milne & Mitrovica (2008) on GIA and sea level

**One name:** Dr. Eric Ivins, JPL — solid Earth / ice sheet coupling. His group works at exactly the intersection of seismology and climate science.
```