Reading Earth's History: Geologic Time Scale and Fossil Evidence

Shared by A STEM Educator

6th GradeClaim-Evidence-ReasoningMS-ESS1-4, MS-ESS2-345 min

Learning Objective

Students will construct evidence-based arguments using the law of superposition, index fossil sequences, and radiometric decay data to make and defend claims about the timing and sequence of events in Earth's geologic history.

Lesson Overview

Students investigate how scientists use rock strata, index fossils, and radiometric data to construct claims about Earth's 4.6-billion-year history. Using a paleontological excavation site context, students practice the full CER cycle from simple relative dating claims to complex mass extinction arguments.

Materials

Rock strata image cards (warm-up sort — see Card Set A)
Index fossil sequencing cards (see Card Set B)
Excavation Site Map handout (printed or projected)
Radiometric decay curve graph (printed — Task 6)
CER writing frame handout
Colored pencils (for annotating strata diagrams)
Sticky notes (for gallery walk annotations)
Four-Quadrant consolidation note sheet (printed)

Scaffolded Task Progression

1Task 1

**Warm-Up Claim Task — Rock Layer Ranking** The diagram below shows four rock layers at Excavation Site 7. Use the law of superposition to rank the layers from oldest (1) to youngest (4), then write a one-sentence claim identifying which layer is oldest. ```coordgraph {"title":"Excavation Site 7 — Rock Strata Cross-Section","xLabel":"Width (meters)","yLabel":"Depth (meters)","xRange":[0,10],"yRange":[0,8],"xStep":1,"yStep":1,"rects":[{"x":0,"y":6,"w":10,"h":2,"fill":"#d4e8c2","stroke":"#4a7c2f"},{"x":0,"y":4,"w":10,"h":2,"fill":"#c8d8f0","stroke":"#2a5fa0"},{"x":0,"y":2,"w":10,"h":2,"fill":"#f0dca0","stroke":"#a07820"},{"x":0,"y":0,"w":10,"h":2,"fill":"#d0b8a0","stroke":"#7a4a20"}],"points":[{"x":5,"y":7,"label":"Layer A"},{"x":5,"y":5,"label":"Layer B"},{"x":5,"y":3,"label":"Layer C"},{"x":5,"y":1,"label":"Layer D"}]} ``` Write your claim: 'I claim that Layer ___ is the oldest because...'

2Task 2

Excavation Site Claim — Which Fossil Is Older?

Your field notes show:
- Layer A (top, green): flowering plant pollen, small mammal teeth
- Layer B (middle, blue): ammonite shells, mosasaur bones
- Layer C (bottom, tan): trilobite fragments

Make a claim: which organism lived on Earth FIRST — the mosasaur or the trilobite? Write your claim using the sentence frame provided.

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