RockLicker · Grade 7 · Lesson 3 of 5

A Missing Chapter in the Rocks

Build a relative sequence that includes erosion and explain the uncertainty of a missing interval.

  • Grade 7
  • 55 minutes
  • Worksheet + teacher guidance
Back to Grade 7

What you will learn

An unconformity can mark erosion or non-deposition in the geological record. Cross-cutting and cover relationships order events but do not tell how much time is missing without additional evidence.

Words to use

  • unconformity: a gap in the rock record
  • fault: fracture with displacement
  • truncate: cut off

Evidence for this lesson

Imaginary relationships: A lies below B; fault F offsets both. Surface E truncates B and the top of F. Layer C covers E and is not faulted. No numerical ages are provided.

Use the supplied record as written; do not invent missing results.

Work through the activity

  1. 10 min · Draw relationshipsDraw A below B. Add fault F offsetting A and B. Draw erosion surface E cutting across the tops of B and F, then layer C covering E.
  2. 20 min · Order eventsUse superposition for A and B, fault cross-cutting for F, truncation for E and cover for C. Write a reason for every step.
  3. 15 min · Read the gapExplain that erosion may remove previously formed material. Distinguish evidence of a gap from evidence of its duration.
  4. 10 min · Revise a scenarioImagine F also offsets C. Explain how that new observation would require later fault movement and could record more than one fault event.
RockLicker
GRADE 7 · LESSON 3

A Missing Chapter in the Rocks

Draw on the printed sheet or write, type or dictate your response.
Draw on the printed sheet or write, type or dictate your response.
Draw on the printed sheet or write, type or dictate your response.
Draw on the printed sheet or write, type or dictate your response.

Responses stay in this open page only. Print before closing or changing pages; no student record is stored online.

Check your understanding

An erosion surface below C tells the exact length of the missing time.

Teacher & family guide · answers and assessment

Grade 7 · A Missing Chapter in the Rocks

Learning goal: Build a relative sequence that includes erosion and explain the uncertainty of a missing interval.

Expected responses

  1. Check lower layers, F offset, E truncation and C cover.
  2. A, B, F, E, C for the stated simple sequence.
  3. An erosion gap; no duration or numerical age is supplied.
  4. Fault movement occurred after C as well; an older fault could have been reactivated.

Understanding check: False; numerical constraints are missing. A gap can be recognized without knowing how long it lasted.

Watch for this misconception

A fault can move more than once. A single neat event order is a model, not every outcrop’s full history.

Assess the evidence

Look for the observations, calculation or explanation named in the learning goal. Accept accurate drawings and dictated responses. Use the expected responses to discuss reasoning; a correct guess without explanation is a starting point for another conversation.

Adapt and extend

Read prompts aloud, enlarge print or let a partner record the learner’s explanation. List additional observations needed to distinguish one fault event from repeated motion.