Learning target: I can use observations and lab data from two rock samples to argue whether a rock was changed by heat and pressure while solid, or melted and re-formed, and explain the energy behind the change.
Read the scenario, then study the evidence table carefully; every row matters. Answer the warm-up questions first, because they organize the evidence for you. Then write your Claim, Evidence and Reasoning in the boxes. A strong response uses specific numbers and observations from the table, says what each piece of evidence rules out, and explains where the energy for the change came from.
You will need: This worksheet, Pencil, Scrap paper for the two-column test
Kettle Ridge is a long hill of dark gray, thinly layered rock. At its west end, a mass of pink crystalline rock (an old intrusion, now exposed by erosion) pushes into the gray rock. A geology student, Priya, collects two samples of the gray rock: Sample F, from 3 kilometers east of the pink rock, and Sample N, from 20 meters from the contact with it. Sample N looks different: harder, shinier, with a faint wavy banding. Priya's question is simple to ask and harder to answer: did Sample N melt and then re-harden, or was it changed while it stayed solid? Her field notes and lab results are below. The site and numbers are a teaching case built from patterns geologists see at real contacts.
| Feature | Sample F (3 km from the pink rock) | Sample N (20 m from the pink rock) |
|---|---|---|
| Layering | Thin, flat layers 2 to 5 mm thick | Layers still present, but bent into gentle waves and thinned to 1 to 3 mm |
| Fossils | Small shell outlines, common | Faint, stretched shell outlines, rare |
| Crystal size and arrangement | Too small to see (under 0.05 mm), no preferred direction | 0.5 to 1 mm, flattened, nearly all lined up in the same direction |
| Silica content (lab) | 61 percent | 60 percent |
| Glass or gas bubbles | None | None |
| Boundary with the pink rock | Not in contact | Sharp line; no mixing of gray and pink rock across it |
| Highest temperature the sample ever reached (lab estimate) | About 100 °C | About 500 °C |
| Temperature at which this rock begins to melt (lab) | About 700 °C | About 700 °C |
On scrap paper, make two columns headed 'If it melted, I would expect...' and 'If it changed while solid, I would expect...'. Under the first, write: no layers, no fossils, brand-new crystals growing in all directions, maybe glass or bubbles, temperature above the melting point. Under the second, write: layers and fossils kept but squashed, crystals regrown and lined up by pressure, temperature below the melting point, sharp boundary with the heat source. Then go down the table row by row and put a check in the column each row matches. Your evidence section is the list of checks.
The pink rock has interlocking crystals 6 to 10 mm across and no layers. Write a second, shorter CER for the pink rock: what it is, how you know, and what its crystal size tells you about where and how slowly it cooled. Then explain how the pink rock and Sample N together show two different routes of the rock cycle driven by the same energy source, and describe what must have happened to the land for both to be at the surface today.