Unit 4 · Earth's Restless Surface · Week 4
How does solid rock become sand — and become rock again?
A canyon wall shows hundreds of distinct layers of different-coloured rock. A nearby river carries tiny grains of sand. A beach is made of sand that used to be cliffs. Where did all that solid rock go — and can it ever come back?
Start here
How we work this lesson (our expectations)
- Rock seems permanent — today we challenge that assumption with evidence
- We follow the matter: rock doesn't disappear, it transforms and moves
- Cycles are everywhere in science — this is a big one
- All supports are always available — open any panel you need
30-second check-in self-management
Before we start: hold a piece of sand (or imagine you are). That tiny grain was once part of a mountain. How does that feel to think about? Geologists find that image deeply satisfying — the idea that nothing in the Earth system is ever truly lost, just rearranged. Take a breath. Let's follow where the mountain went.
Do-Now Spiral retrieval
Three questions spiraling Weeks 1–3 and Unit 1. Pull from memory first.
- Unit 1 spiral From Unit 1: matter is never created or destroyed — it is rearranged. A log burns, and the solid wood seems to disappear. Where does the matter go? (Use what you know about conservation of matter.)
- Week 3 spiral At a convergent plate boundary, two continental plates collide and crumple into each other. What landform is created? (Use the seashell fossil mountain from Week 1 as a hint.)
- New: Look at your hand. In your best guess, what is your skin made of? Have any of those atoms ever been part of a rock? (Best guess — there is no wrong answer here.)
The phenomenon
Stand at the rim of the Grand Canyon and look down: you can see nearly two billion years of Earth history in the rock layers below you. Each layer is sediment — sand, silt, or mud — that was once loose material carried by water or wind and then compressed into solid stone. The limestone at the canyon's rim contains seashell fossils (the ocean again!). Below it are layers of sandstone that were once desert dunes. Below that, old metamorphic and igneous rock from when Arizona was near a plate boundary long ago. Every single layer you see was once something else — a beach, a river delta, an ancient seafloor, a volcanic eruption. The material did not appear from nowhere, and it did not vanish when it became something new. It was rearranged. Water, ice, wind, and gravity continuously break rock apart and carry it somewhere else. Heat and pressure deep underground transform loose sediment back into solid rock. The mountain you are standing on is the same matter that was once a seafloor, and will someday be sand again. Our question: what processes break rock down and carry it away — and can the matter ever come back as new rock?
The Grand Canyon has layers of rock that were once beaches, riverbeds, and ocean floors — then got buried and turned to stone. Water, ice, and wind break down solid rock into tiny pieces (weathering). Those pieces are carried away (erosion) and pile up somewhere else (deposition). Over millions of years, the piled-up layers get compressed into new rock. The rock is never destroyed — it just keeps changing form. What breaks rock down — and can it become rock again?
Notice & Wonder. Write one thing you notice about the diagram — where does the matter end up? Write one thing you wonder about whether the matter is ever truly "gone."
Build it Weathering, erosion, deposition, and the rock cycle
Four linked processes that together show how matter is rearranged — never destroyed — at Earth's surface.
Step 1 — Weathering: breaking rock without moving it
Weathering is the breakdown of rock at or near Earth's surface. Mechanical weathering breaks rock into smaller pieces without changing its chemical composition — for example, water seeps into a crack, freezes, expands, and pries the rock apart (ice wedging). Chemical weathering changes the rock's minerals into new substances — for example, rainwater (slightly acidic) dissolves limestone, or oxygen reacts with iron in rock to form rust. Both types leave the matter right where it is — they just break it into smaller pieces or change what it is made of at the chemical level.
Weathering breaks rock apart without moving it. Mechanical: water freezes in cracks and splits the rock. Chemical: rain dissolves some rocks or rusts iron-rich rocks. The matter stays nearby — it just becomes smaller pieces or changes chemically.
Step 2 — Erosion, deposition, and the rock cycle
Erosion is the movement of weathered material by water, wind, ice (glaciers), or gravity. Deposition is when that material settles and accumulates somewhere else — in a river delta, at the bottom of a lake, on the ocean floor. As more sediment piles up, the layers below are squeezed under immense pressure. Over millions of years, that pressure (and sometimes heat) transforms loose sediment into solid sedimentary rock — a process called lithification. If that rock is buried deeper and subjected to even more heat and pressure, it can become metamorphic rock. If it melts completely, it becomes magma that can cool into igneous rock. If tectonic forces push it back to the surface, the whole cycle starts again. This is the rock cycle — and it is an example of matter being conserved: no rock is ever truly created or destroyed, only rearranged into a different form.
Erosion moves the pieces (water, wind, ice). Deposition drops them somewhere else. Piled-up layers get squeezed into sedimentary rock. More heat and pressure = metamorphic rock. Melt it = magma = igneous rock when it cools. Push it back up by plate tectonics = starts over. This loop is the rock cycle. Matter is never destroyed — just changed and moved.
Worked example — tracing a grain of sand through the rock cycle
Start: A granite boulder sits on the side of a mountain.
Weathering: Rain seeps into cracks each winter. Ice forms, expands, widens the cracks. Over 10,000 years, the boulder breaks into pieces. Rainwater reacts with feldspar in the granite, forming clay minerals.
Erosion: Spring snowmelt carries sand-sized quartz grains (resistant to chemical weathering) down the slope into a river.
Deposition: The river loses energy as it reaches flat land. The grains settle on the riverbed, then at a delta. More material piles on top.
Lithification: Over millions of years, the grains are cemented by minerals in the water and compressed — sandstone forms.
Burial & uplift: Plate tectonics buries the sandstone deeper; it becomes metamorphic rock (quartzite). Eventually, uplift (same process as the Himalayas, Weeks 1–3) brings it back to the surface. Rain begins to weather it again.
The quartz atoms that started in that granite boulder are still in the quartzite — rearranged, moved, transformed, never destroyed.
Show me the rock cycle as a diagram Tier 2 · visual
Draw three boxes in a triangle: top = "Sedimentary rock," bottom-left = "Metamorphic rock," bottom-right = "Igneous rock." Draw arrows between them and label each arrow with the process that causes the change: weathering+erosion+deposition+lithification (from igneous/metamorphic → sedimentary); heat+pressure (from sedimentary → metamorphic); melting+cooling (from metamorphic → igneous); uplift (from igneous → surface). In the center, write "Matter conserved: only the form changes." This triangle summarizes the whole rock cycle.
Your turn Where did the mountain's matter go?
Use a Claim–Evidence–Reasoning format or the systems model. Choose your response mode — all are equally valid.
The task: The Himalayas (formed by two plates colliding, Week 3) are slowly being eroded. A student says "the mountain will eventually be destroyed — the matter will be gone." Use the rock cycle to correct this misconception and explain where the matter actually goes, and whether it can ever become a mountain again.
I want sentence starters Tier 2 · frames
Claim: The mountain's matter is not destroyed — it ________.
Evidence: When rock weathers, it breaks into ________. Erosion moves those pieces by ________. They are deposited at ________.
Reasoning: The matter can become rock again because ________. Over deep time, plate tectonics could ________ that new rock back to the surface, where ________ could happen again. This shows that matter is ________, not destroyed.
Word bank: weathering · erosion · deposition · lithification · sedimentary · metamorphic · igneous · cycle · conserved · uplift · pressure · compacted · fragments · sand · river · ocean · matter
Let's make it concrete first Tier 3 · re-teach
Analogy: Imagine a pile of building blocks (the mountain). Wind and rain slowly knock blocks off (weathering). Kids carry the blocks down the hall (erosion) and dump them in a pile in the corner (deposition). A teacher then stacks the blocks tightly and puts a heavy book on top (lithification — new rock). Later, someone moves the stack back into the original room (uplift by tectonics). The blocks didn't disappear — they just moved and got rearranged. Matter in the rock cycle is exactly like this: the same atoms just keep moving and changing form.
Fill in: When the mountain weathers, rock breaks into ____. Water carries those pieces ____ (erosion). They pile up and are pressed into ____ (deposition + lithification). Over time, tectonics can push them back up (____), and the cycle ____. Matter is ____, not gone.
Push my thinking Extension
The rock cycle operates on timescales from thousands to hundreds of millions of years. Design a mathematical estimate: if a mountain is being eroded at 4 mm per year (a reasonable geological rate), how many years would it take to erode 4,000 metres of rock (roughly the height of the Alps)? Now research: the Alps are also still rising at about 1 mm per year due to ongoing plate collision. What is the net change per year? How does this change your prediction? What does this tell you about how the rock cycle and the plate tectonic cycle interact — and why mountains can persist for tens of millions of years?
Check yourself Did it click?
- describe weathering, erosion, deposition, and lithification and put them in order;
- name the three types of rock and explain one process that converts one type to another;
- explain that matter is conserved in the rock cycle — no rock matter is ever truly created or destroyed, only rearranged.
A student says: "Sand is just destroyed rock — once a mountain erodes to sand, that matter is gone for good." What is wrong with this reasoning?
Re-teach: rock matter is conserved — the cycle never stops Tier 3
Conservation of matter in the rock cycle: From Unit 1, you know that matter (atoms) is never created or destroyed — only rearranged. The rock cycle is this principle applied to Earth's surface materials.
The path from mountain to sand to rock again: (1) Mountain rock is weathered (broken into pieces). (2) Erosion carries those pieces to a new location. (3) Deposition piles them up. (4) Lithification squeezes them into sedimentary rock. (5) Deeper burial adds heat and pressure → metamorphic rock. (6) Melting → magma → igneous rock. (7) Tectonic uplift brings it back to the surface. The atoms that were in the original mountain are still in that igneous rock — same matter, different form and location.
The key word to replace "destroyed" with: rearranged. Rock matter is rearranged and relocated, not destroyed.
Reflect, then show what you know
Reflection metacognition + self-awareness
Think of something that looks permanent to you right now — a building, a road, a cliff you have seen. Using the rock cycle, describe what will happen to it over deep time. There is no wrong answer — this kind of thinking across time scales is what geologists, climate scientists, and engineers all practice.
Exit ticket — answer on paper or in your notebook.
- New Put these four processes in order and describe what each one does: weathering, erosion, deposition, lithification.
- New A geologist finds a layer of sandstone on a mountainside. Trace the journey that sand took before it became the rock this geologist is now looking at. Include at least three steps from the rock cycle.
- Spiral — Unit 1 In Unit 1 we said matter is never created or destroyed, only rearranged. Give one specific example from today's lesson that proves matter is conserved in the rock cycle.
- Spiral — Weeks 1–3 The mountain in this week's phenomenon was created by plate tectonics (Weeks 1–3). How does understanding the rock cycle complete the explanation of why the same mountain holds seashell fossils at its peak? (Connect the fossil story all the way through: seafloor → uplifted → weathered → the seashell is now in a rock layer.)
- Transfer Next week you will assess whether a location is safe to build on using everything from this unit. Think about a location near a river delta where thick layers of sediment have built up over time. What natural hazards would you look for there — and how does the rock cycle affect the stability of the ground? (Best guess — we will use this thinking next week.)
Educator panel — facilitation, accommodations, answer key
At a glance
Standards: NGSS MS-ESS2-1 (develop a model to describe the cycling of Earth's materials and the flow of energy that drives this process) and MS-ESS2-2 (construct an explanation based on evidence for how geoscience processes have changed Earth's surface at varying time and spatial scales). 3D: SEP Developing & Using Models + Constructing Explanations · DCI ESS2.A Earth Materials & Systems + ESS2.C Roles of Water · CCC Energy & Matter (conservation) + Stability & Change + Systems & System Models. Throughline: Conservation of matter (Unit 1) applied to geological cycles; the rock cycle completes the seashell fossil story (Weeks 1–3) and provides the matter-tracking foundation for the Week 5 performance task.
Facilitation arc (Rosenshine)
- Open with student predictions from Week 3 exit ticket about rock erosion (3 min).
- Do-Now retrieval — item 1 specifically recalls Unit 1 conservation of matter to prime the throughline (3 min).
- Build Steps 1–2 with the worked example (granite grain journey); cold-call on each process (12 min).
- Differentiated CER/model — circulate; prompt "can you show where the matter ends up at each step?" (15 min).
- Self-check + re-teach branch (5 min).
- Brain break (grain-of-quartz roleplay), reflection, exit ticket (10 min).
IEP / 504 accommodation cards
Common accommodations mapped to this lesson
| Accommodation | How it's already built in / what to do |
|---|---|
| Text read aloud | Every passage has a Listen button (TTS); simplified toggle shortens it. |
| Reduced reading load | "Reading: Simplified" swaps in plain-language text. |
| Chunking / extended time | Small steps with checks; progress saves automatically. |
| Sentence frames / word bank | Tier-2 panel provides both for the CER/model task. |
| Concrete manipulatives / models | Tier-3 "building blocks" analogy; physical sand and rock samples if available. |
| Alternative response mode | Students may draw the rock cycle diagram, speak/record, or write the CER — all accepted. |
| Behavior / focus (504, ADHD) | Named expectations (PBIS), 30-sec check-in, built-in grain-of-quartz movement activity. |
| Multilingual / EL | Simplified text, SVG visual diagram, word bank, home-language reflection allowed. |
Exit ticket answer key
- Order and descriptions: (1) Weathering — rock is broken into smaller pieces or chemically altered at or near the surface; (2) Erosion — those pieces are moved by water, wind, ice, or gravity; (3) Deposition — the pieces settle and accumulate somewhere else; (4) Lithification — accumulated sediment is compacted and cemented under pressure into sedimentary rock.
- A strong answer traces: loose sand or sediment was weathered from an earlier rock (e.g., granite), eroded by a river or wind, deposited at the bottom of a body of water (river delta, lake, or ocean floor), accumulated in layers, and compacted and cemented over millions of years into sandstone. Tectonics then uplifted that sandstone to the mountainside where it is found today.
- Accept any example that shows the atoms remain: the quartz atoms in granite are still in the sandstone after weathering and lithification; the feldspar minerals in granite are chemically altered but the atoms are still in the clay minerals produced; the mass of sand at the bottom of the ocean equals the mass that eroded from the mountain (if we could track it in a closed system).
- Strong answers connect: the seashell was on an ancient seafloor (ocean sediment) → the seafloor was uplifted by converging plates (Weeks 1–3) → as the mountain formed and rose, rain and ice weathered the surface rock → the weathering exposed the sedimentary layer that contained the fossil → the fossil shell is still in the rock layer because it was cemented in during lithification. The seashell's matter was carried upward with the rock — it didn't fly there, the whole rock layer moved.
- Predictions will vary — accept any that include: river deltas have loose sediment that has not been lithified (soft, compressible ground); liquefaction risk during earthquakes; flooding from river overflow; potential for land subsidence if water is extracted. The rock cycle connection: unconsolidated sediment (not yet lithified) is unstable for building compared to solid bedrock.
Why it's designed this way
The rock cycle is one of the clearest illustrations of the year-long CCC Energy & Matter throughline: matter is never created or destroyed, only rearranged. The self-check targets the "rock is destroyed" misconception, which is among the most persistent in Earth science (Keeley, 2005). The Do-Now explicitly retrieves Unit 1's conservation principle (spacing effect, P6) so students apply it to the new geological context — this is the interleaving design prescribed by Rohrer (2012). The worked example (grain-of-quartz journey) demonstrates a complete rock cycle path before students attempt to build one, managing cognitive load (Sweller, 1988). Exit ticket item 4 requires students to synthesize all four weeks' learning in a single explanation — this is the readiness check for the Week 5 performance task.