Teacher answer key · Grades 6–10 · about 15 minutes

Answer key: Rock Cycle Journey Activity

For teachers. This page is hidden from search engines and not linked from student pages, but it is not password-protected, so please don’t share the link with students. Student worksheet: Rock Cycle Journey Activity.

Goal: Follow one rock through the rock cycle in a model: record what each process makes, where in Earth it happens and how hot it gets, and name the energy that drives each change.

Connects to NGSS MS-ESS2-1 (Develop a model to describe how Earth’s materials cycle and the flow of energy that drives this cycling.)

Completed results table

Values come from the builder’s Conditions panel and are rough ranges; accept answers close to them. Sediment and magma are not rocks yet, so they belong to no rock family.

Process	You get	Family	Where it happens	About how hot?
1. Uplift and exposure	Granite	Igneous, intrusive	At the surface, on land	Surface temperature
2. Weathering and erosion	Sediment	Sediment (not rock yet)	At the surface	Surface temperature
3. Deposition: mud in quiet water	Mud layers	Sediment (not rock yet)	Quiet water: a lake, lagoon or the deep sea floor	Surface temperature
4. Compaction and cementation	Shale	Sedimentary	Buried under younger layers, 1–5 km down	25–125 °C
5. Heat and pressure: medium grade	Schist	Metamorphic	Deep under a mountain range, 16–24 km down	400–600 °C
6. Melting	Rhyolitic magma	Magma (molten rock)	Deep in the crust, 26–32 km down	650–800 °C

Answers vary. Slowly underground: Granite. Quickly as lava: Rhyolite. Very quickly, into glass: Obsidian. Full of gas bubbles: Pumice.

Answers

Which step turned loose material into solid rock? What two things happened to make it solid?
Compaction and cementation (step 4) made shale. The weight of the layers above squeezed the mud grains together (compaction), and minerals left by water glued them (cementation).
Which steps happened at the surface, and which deep underground? What energy drives each group?
At the surface: weathering and erosion, and deposition. Energy from the Sun drives the weather and moving water, and gravity moves the grains downhill. Underground: compaction and cementation, heat and pressure, and melting, driven by Earth’s internal heat and the weight of the rock above. Uplift links the two: Earth’s heat drives the plate motions that lift mountains, and erosion uncovers the rock.
The crust gets about 25 °C hotter per km down. Your shale became schist at about 500 °C. How deep was it?
500 ÷ 25 = 20 km down. That fits the builder’s range for medium grade, 16–24 km.
At 1 mm per year of uplift (1 km per million years), how long would the schist take to reach the surface?
20 km at 1 km per million years takes 20 ÷ 1 = 20 million years.
Your journey ended as magma. Name two different rocks it could become, and say how each would cool.
Cooling slowly underground makes granite, with big crystals. Cooling quickly as lava makes rhyolite, with tiny crystals. Cooling very quickly makes obsidian (glass), and lava full of gas makes pumice.
A classmate says rocks always go igneous → sedimentary → metamorphic. Find a shortcut in the builder and describe it.
There is no fixed order. For example, granite can go straight to gneiss with high-grade heat and pressure (igneous to metamorphic), sandstone can be uplifted and weathered into new sediment (sedimentary back to sediment), and basalt can melt again without ever becoming sedimentary.

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