Skill: course-build → write-mcqs → write-explanation, design-check-sequence @ b0fa825; v2 (2 Oct 2026, evening) after the guidance, blind-read and figure reviews @ efd8fba
Topic 21 — How rock layers tell the time — the PP100's twelve question types, with their exemplars
What this page is. James reads a bank as its question TYPES first (vault: A bank is reviewed as its question types first, one exemplar each). Under the Grade 4 standing brief the bank is built straight away (50 items in content/G4T21_pp100_bank.py; v2 cut the typed "layer" item — it tested Topic 18's word and its stem printed two of its own accepted answers); this sheet is the way in. Each type line says what the stem asks, what the four options (or the accept list) are, and prints one exemplar in full.
Rulings already applied. Four options on every MCQ; no option bundles a verdict with its reason (claims are 'which sentence is true' with the claim in the stem, or bare yes / no in the quizzes); every stem is a positive question, at most two sentences below hard; a drawn cliff on an item names its layers by letters outside A–D and its blind text lists the bands TOP TO BOTTOM with their colours and contents — never "oldest", "youngest", "older", "younger", "first", "last" or "order" (grep of the bundle's [Drawing: lines → 0); the hard tier is typed where typing produces (a position number counted from a drawing; the count of layers above a lettered layer) and a chained MCQ elsewhere; every drawn item's stem, options, key, fb and why are built from the SAME list as its figure (figures.ITEM_CLIFFS, top → bottom, through words()), so a letter cannot point at two things; every claim-maker (Jordan, Karl, Julia) appears once in the bank; US spelling; no term is coined in this topic, so there is no term-recall type.
The bar list (real things a generated item must never name, because the taught class claim would break): tilted, folded or broken layers, or a cliff drawn with slanting bands (the rule is for layers that still lie flat); a layer "turned upside down"; any number of years for a whole cliff or a fossil (deep time is "a very, very long time"; one layer is "hundreds or even thousands of years"); a fossil that "sank" as a TRUE statement; the Grand Canyon, a road cut, a jar, a notebook, a river-cut hillside near a school (the lessons' own scenes); a cave stalactite or an icicle as "a layer"; volcanic ash or lava as a layer (igneous rock is Topic 18's and never "settles"); a fossil described as the living animal; "pulled back" of the sea; a dinosaur name as the fossil (Grade 3 Topic 27's footprint is "a footprint", not a named dinosaur); "strata", "superposition", "index fossil", "geologic time" (grades 6-8).
The twelve types
| Type | Items | Atom | Tags | Form | The stem asks… | The options / the accept | Exemplar scene |
|---|---|---|---|---|---|---|---|
| 1 | 6 | EAR4-035 | easy | MCQ; three drawn | which layer formed first / last, or is the oldest / youngest, in a drawn or described cliff | layers by letter (J K L M N P), or the fixed position set SAME4 (top / second from top / second from bottom / bottom), with "formed at the same time" as the fourth where letters run short | a quarry wall in Indiana; a sea cliff in California; a swimming-pool hole in Florida; a lakeside cliff in Michigan; a mine wall in Colorado |
| 2 | 3 | EAR4-035 | easy, medium | MCQ | where a new layer lands; how long one layer takes; why the bottom layer is the oldest (four reasons) | four places / four spans of time / four single-statement reasons | a lake floor with three mud layers and a flood |
| 3 | 4 | EAR4-035 | medium, hard | MCQ | which sentence is true when two layers lie one on the other, when a thick layer lies under a thin one, when a claim of one afternoon is made; the oldest of three layers given two relations | four single statements, or letters | Jordan's one-afternoon claim; K under J and on top of L |
| 4 | 8 | EAR4-036 | easy, medium, hard | MCQ; two drawn | which layer gets number 1 / number 3; which is the youngest / oldest by number; which number the top layer gets; which layers a numbered layer formed after; what a top-down count means | letters, or numbers 1–6 ascending, or four single statements | a cut behind a new store in Georgia; a railroad cut in Missouri; two cliffs side by side |
| 5 | 2 | EAR4-036 | medium | reorder, drawn | tap the layers from first formed to last (both items; the key is stored first → last, bottom → top) | the layers' letters in the authored order | a ditch in Kansas; a mountainside in Utah |
| 6 | 2 | EAR4-036 | medium, hard | typed numeric, drawn | the number a lettered layer gets counting from the bottom; how many layers formed after a lettered layer | the bare number and its word (4 / four; 2 / two) | six-layer and five-layer cliffs lettered out of order |
| 7 | 6 | EAR4-037 | easy, medium, hard | MCQ; four drawn (v2: PP-32's cliff is fresh — a bone above a footprint) | which fossil is older / younger given its layers; about how old a fossil is; two positions counted from opposite ends | the two fossils + "both the same age" + a fourth, or four single statements | a cave wall in Kentucky; an island cliff in Maine; the second layer from the top against the second from the bottom |
| 8 | 2 | EAR4-037 | medium | MCQ | why a fossil is deep; which pieces buried a fossil (v2) | four single-statement reasons / four sets of pieces | a fish fossil under six layers |
| 9 | 3 | EAR4-037 | medium, hard | MCQ | which sentence is true of a claim about fossil age (top = oldest; same layer, far apart; how a bottom fossil got there) | four single statements | Karl's top-layer claim; a quarry wall one hundred meters long |
| 10 | 5 | EAR4-038 | easy, medium | MCQ; one drawn | what the place was like when a described layer formed; which layer tells the first part; which layer tells the last part (v2) | four places (under the sea / a forest / a sandy shore / a desert or frozen place), or letters | a layer full of sea shells; a layer of fern prints |
| 11 | 5 | EAR4-038 | medium, hard | MCQ; three drawn | how the place changed (two layers); which sentence tells the story (three to five layers, one reading repeated, one return to the sea) | four whole-sentence stories | footprint under shells; three fish layers under tree roots; shells, shells, ferns, shells |
| 12 | 3 | EAR4-038 | hard | MCQ | judge a story read in the wrong direction; the middle of a sea–sand–sea story; two cliffs' stories compared | four single statements | Julia's trees-first claim; sand with footprints between two shell layers; Alabama against Nevada |
Difficulty by atom (easy / medium / hard): EAR4-035 8 / 4 / 1 · EAR4-036 6 / 5 / 2 · EAR4-037 3 / 6 / 2 · EAR4-038 2 / 5 / 6 (50 items). Keys on the 46 four-option MCQs: A 9 · B 14 · C 12 · D 11.
One exemplar per type
Type 1 — which layer formed first (drawn)
Stem. A quarry wall in Indiana shows layers J, K and L. Which layer formed first?
Figure. pp_cliff_1 — blind: cliff with 3 flat layers, top to bottom: K cream shell rock; J gray mud; L tan sand (v2: the lettering is shuffled, so "bottom = last letter" is not a shortcut). (Nearest lesson-side instance: L01 q3, cliff J K L at the road cut lesson — a different cliff, different colours, letters in a different order.)
Options. J / K / L / K and L formed at the same time
Why. In rock layers that still lie flat, the bottom layer formed first. L is the bottom layer. So L formed first.
Tag. easy · EAR4-035
Type 2 — why the bottom layer is the oldest
Stem. A cliff shows flat layers of rock. Why is the bottom layer the oldest?
Options. Heavy rock always sinks to the bottom. / Every other layer landed on top of it after it formed. / The bottom layer is darker than the others. / The bottom layer is pressed the hardest.
Why. Each new layer of pieces landed on top of the layers already there. The bottom layer was there before every other layer landed. So the bottom layer is the oldest.
Tag. medium · EAR4-035 (nearest lesson-side instance: L01 q6 "which layer is older" — that item asks the verdict; this one asks the reason)
Type 3 — which sentence is true (two relations, no drawing)
Stem. In a cliff of flat layers, layer K lies under layer J and on top of layer L. Which layer is the oldest?
Options. J / K / L / all three are the same age
Why. K is under J, so K formed before J. K is on top of L, so L formed before K. So L is the lowest layer, and L is the oldest.
Tag. hard · EAR4-035 — hard because two relations must be combined to find the bottom layer with no picture.
Type 4 — which layer gets number 1 (drawn)
Stem. A hill behind a new store in Georgia was cut away, and the cut shows layers J, K, L and N. Which layer gets number 1 in time order?
Figure. pp_cliff_3 — blind: cliff with 4 flat layers, top to bottom: K tan sand; L gray mud; N red-brown sand; J cream shell rock.
Options. J / K / L / N
Why. To put rock layers in time order, start at the bottom layer and count up. J is the bottom layer. So J gets number 1.
Tag. easy · EAR4-036 (nearest lesson-side instance: L02 q2 on cliff J K L M — a different cliff, the bottom letter different)
Type 5 — reorder, first formed to last
Stem. A deep ditch dug in Kansas shows layers J, K, N and P. Tap the layers in time order, from the layer that formed first to the layer that formed last.
Figure. pp_cliff_12 — blind: cliff with 4 flat layers, top to bottom: K cream shell rock; P red-brown sand; J gray mud; N tan sand.
Answer. N, J, P, K
Why. To put rock layers in time order, start at the bottom layer and count up. N is the bottom layer, then J, then P, and K is on top. So the order is N, J, P, K.
Tag. medium · EAR4-036 (nearest lesson-side instance: L02 q5 reorder on cliff K L M N P — a different cliff; the sister item PP-25 asks the same direction on a three-layer cliff; v2 — v1's last-to-first ask fought the widget's "Tap the first one first.")
Type 6 — type the number (drawn)
Stem. A cliff shows layers J, K, L, M and P. Number the layers in time order from the bottom. How many layers formed after layer P? Type the number.
Figure. pp_cliff_15 — blind: cliff with 5 flat layers, top to bottom: K gray mud; L tan sand; P red-brown sand; J cream shell rock; M gray mud.
Accept. 2 / two / 2 layers / two layers
Why. Start at the bottom and count up: M is 1, J is 2, P is 3, L is 4, K is 5. Layers 4 and 5 formed after layer P. So 2 layers formed after layer P.
Tag. hard · EAR4-036 — hard because the student counts up to P and then counts the layers above it; the number is produced from the drawing, not picked.
Type 7 — which fossil is older (drawn)
Stem. A cave wall in Kentucky shows layers J, K, L and M, with a fish fossil in layer J and a footprint in layer L. Which sentence is true?
Figure. pp_cliff_4 — blind: cliff with 4 flat layers, top to bottom: M gray mud; L tan sand with a footprint; K cream shell rock; J gray mud with a fish fossil.
Options. The fish fossil is older than the footprint. / The footprint is older than the fish fossil. / The two fossils are the same age. / The fish fossil formed after layer M.
Why. A fossil is about as old as the rock layer it sits in. Layer J is deeper than layer L, so J is older. So the fish fossil is older than the footprint.
Tag. easy · EAR4-037 (nearest lesson-side instance: L03 q3 fish in L against shells in J — a different cliff, the fish now at the bottom)
Type 8 — why a fossil is deep
Stem. A fish fossil sits deep in a cliff, under six layers of rock. Why is the fish fossil so deep?
Options. The fish sank down through the rock after it died. / The fish was buried first, and six layers landed on top later. / Fish always swim to the bottom of the rock. / The six layers pushed the fish down.
Why. Rock is solid, so nothing sinks down through it. The fish was buried as its own layer formed, and six layers landed on top later. So the fish fossil is deep.
Tag. medium · EAR4-037 (nearest lesson-side instance: L03 q6 Julia's sinking claim, bare yes / no — here the reason is the target)
Type 9 — which sentence is true of a fossil-age claim
Stem. Karl says a fossil in the top layer of a cliff is the oldest fossil in the cliff. Which sentence is true?
Options. The fossil in the top layer is the oldest fossil in the cliff. / Every fossil in the cliff is the same age. / The fossil in the top layer is the youngest fossil in the cliff. / A fossil's age has nothing to do with its layer.
Why. A fossil is about as old as the rock layer it sits in. The top layer formed last, so it is the youngest layer. So the fossil in the top layer is the youngest fossil in the cliff.
Tag. medium · EAR4-037
Type 10 — what the place was like when a layer formed
Stem. A layer of rock is full of sea shells. What was the place like when that layer formed?
Options. under the sea / a forest / a desert / a frozen lake
Why. A fossil shows what lived in a place long ago. Sea shells come from animals that live under the sea. So the place was under the sea when that layer formed.
Tag. easy · EAR4-038 (nearest lesson-side instance: L04 q2 "what was the place like when layer J formed" on a drawn cliff — this one is a described single layer)
Type 11 — which sentence tells the story (drawn)
Stem. A cliff shows layers L, M, N and P. Fish fossils sit in layers M, N and P, and tree roots sit in layer L. Which sentence tells the story?
Figure. pp_cliff_8 — blind: cliff with 4 flat layers, top to bottom: L dark brown soil with tree roots; M gray mud with a fish fossil; N gray mud with a fish fossil; P gray mud with a fish fossil.
Options. The place was under water for a short time, and then a forest grew. / The place was under water for a long time, and then it became a forest. / The place was a forest, and then it was under water for a long time. / The place was a forest the whole time.
Why. Read each layer from the bottom up. P, N and M all hold fish, so the place was under water while three layers formed, a long time. L holds tree roots, so the place became a forest.
Tag. hard · EAR4-038 — hard because three layers with the same reading mean a long time, and the order must be read as well.
Type 12 — two cliffs' stories compared
Stem. A cliff in Alabama holds sea shells at the bottom and tree roots on top. A cliff in Nevada holds tree roots at the bottom and sea shells on top. Which sentence is true?
Options. Both places changed in the same way. / Neither place changed. / In Alabama the forest came first; in Nevada the sea came first. / In Alabama the sea came first; in Nevada the forest came first.
Why. Read each cliff from the bottom up. In Alabama the bottom layer holds sea shells, so the sea came first there. In Nevada the bottom layer holds tree roots, so the forest came first there.
Tag. hard · EAR4-038 — hard because two stories are read and then compared.
Draw constraints (⟂ — never in one PP100 draw)
- PP-9 (J gets number 1 on
pp_cliff_3) ⟂ PP-14 (L gets number 3 on the samepp_cliff_3): one drawing, two counts; the first count hands over the second's start. - PP-5 (the oldest of seven layers, SAME4) ⟂ PP-4 (the youngest of four layers, SAME4): the same fixed position set keyed at its two ends.
- PP-21 (two layers one on the other: which sentence is true) ⟂ PP-6 (red sand on gray mud: which formed first): the first states the rule the second applies.
- PP-20 (why the bottom layer is the oldest) ⟂ PP-3 / PP-5 / PP-13 (which layer is the oldest / formed first): the reason item prints the verdict every verdict item asks.
- PP-24 (reorder first → last, four layers) ⟂ PP-25 (reorder first → last, three layers): the same move twice; draw one.
- PP-26 (type N's number on
pp_cliff_14) ⟂ PP-41 (type the count after P onpp_cliff_15): one move, two drawings; draw one. - PP-29 (why a fish fossil is deep) ⟂ PP-44 (how a bottom shell got there) ⟂ PP-30 (which pieces buried a leaf): the burial mechanism asked three ways; two per draw at most.
- PP-18 (sea shells → under the sea) ⟂ PP-50 (Alabama against Nevada) ⟂ PP-48 (Julia's trees-first claim): the first prints the reading the other two chain.
- PP-46 (shells, shells, ferns, shells) ⟂ PP-49 (sand with footprints between two shell layers): both carry a return to the sea.
- PP-43 (second from the top against second from the bottom) ⟂ PP-11 (which layer formed third): the first's why counts the positions the second asks.
The design-move inventory (one line per bank item: MOVE · SCENE KIND · nearest earlier item)
| PP | Move | Scene kind | Nearest earlier item |
|---|---|---|---|
| 1 | read the bottom letter as first formed | a quarry wall, three layers | L01 q3 (road-cut lesson, J K L) — different cliff |
| 2 | read the top letter as last formed | a sea cliff, five layers | L01 q4 (J M N P) |
| 3 | pick the bottom colour as first formed, described | a swimming-pool hole | L01 article (cream at the bottom) — different colours, no road cut |
| 4 | youngest = top, position set | a lakeside cliff | summary Q1 (youngest, three positions) — four positions here |
| 5 | oldest = bottom, position set | a mine wall, seven layers | L01 q10 (canyon wall, three positions) |
| 6 | two described layers, which first | red sand on gray mud | L01 q6 (a lower layer is older) |
| 7 | where new pieces land | a lake floor, four layers, pebbles after a storm (v2) | L01 q5 (sea floor, two mud layers, sand) — the count, the pieces and the water differ |
| 8 | how long one layer takes | none (a fact) | L01 q9 (Karl's thousands of years, yes / no) |
| 9 | number 1 on a drawn cliff | a cut behind a store | L02 q2 |
| 10 | youngest on a drawn cliff | a rock wall above a parking lot (v2) | L02 q6 (J L N) |
| 11 | which layer formed third, described | five layers | L02 q10 (layer 4 before layer 5) |
| 12 | the number of the layer right under the top, nine layers (v2) | described | L02 q7 (the top layer's number) — one step further |
| 13 | youngest by number (v2) | numbered layers 1–5 | L02 q8 (oldest of six, positions) — the other end, by number |
| 14 | number 3 on a drawn cliff | the same store cut, self-contained (v2) | PP-9 (⟂) |
| 15 | which fossil is older, drawn, as sentences | a cave wall | L03 q3 |
| 16 | which fossil is younger, drawn | an island cliff | L03 q4 |
| 17 | about how old a fossil is | a fact | L03 q2 (when buried) |
| 18 | read one layer: shells → sea | a described layer | L04 q2 |
| 19 | read one layer: ferns → damp forest | a described layer (v2: the stem no longer says damp, shady) | L04 article (second cliff) — the reading alone |
| 20 | the reason the bottom is oldest | none | L01 q6 (verdict) |
| 21 | which sentence is true: two layers | none | L01 q6 |
| 22 | thickness is not age | a thick layer under a thin one | NEW |
| 23 | one-afternoon claim as sentences | Jordan | L01 q7 (same-time claim, yes / no) |
| 24 | reorder first → last, drawn | a ditch | L02 q5 |
| 25 | reorder first → last, drawn, three layers (v2) | a mountainside | PP-24 (⟂) |
| 26 | type the number a letter gets | six layers | PR-7 (type the top layer's number, described) |
| 27 | what a top-down count means | a geologist counting down | L02 q9 (Karl numbers from the top, yes / no) |
| 28 | first formed in two cliffs of different sizes | two cliffs side by side | NEW |
| 29 | why a fossil is deep | a fish under six layers | L03 q6 (sinking claim) |
| 30 | which pieces buried a fossil (v2) | a leaf print in a five-layer cliff | L03 q2 (when it was buried) — the pieces, not the moment |
| 31 | which fossil is older, drawn, as sentences | a three-layer cliff | L03 q3 |
| 32 | which fossil is younger, drawn | a bone above a footprint, letters J K P (v2: fresh; v1 was L04's cliff inverted) | L03 q4 |
| 33 | top fossil = oldest claim as sentences | Karl | L01 q8 (Julia's top-is-oldest, for layers) |
| 34 | same layer, far apart | a quarry wall one hundred meters long | L03 q5 (left and right ends) |
| 35 | two-layer change, drawn | footprint under shells | L04 q6 (roots under shells) |
| 36 | which layer tells the first part, drawn | a four-layer cliff | L04 q4 |
| 37 | two-layer change, described | ferns under shells | PR-12 FRQ (ferns under shells) — the MCQ form |
| 38 | the middle of a three-layer story | shells, sand, roots | L04 article (worked case) — the middle alone |
| 39 | which layer tells the last part (v2) | a class reading a four-layer cliff | L04 q4 (first part) — the other end |
| 40 | oldest from two relations, no drawing | K under J on L | NEW |
| 41 | type the count of layers above a letter | five layers | PP-26 (⟂) |
| 42 | which layers a numbered layer formed after | numbers 1–6 | L02 q10 |
| 43 | positions from opposite ends | five layers | NEW |
| 44 | how a bottom shell got there, as sentences | a shell under four layers | L03 q6 |
| 45 | three repeated readings then a change, drawn | three fish layers under roots | L04 q7 (two shell layers under a footprint) |
| 46 | four readings with a return, described | shells, shells, ferns, shells | NEW |
| 47 | five layers, two repeated readings, drawn | roots, sand, shells, shells, fish | L04 q5 |
| 48 | judge a story read top-down | Julia | L04 q10 |
| 49 | the middle of a sea–land–sea story | sand with footprints between shells | NEW |
| 50 | two cliffs' stories compared | Alabama and Nevada | NEW |