Learning target: I can construct a scientific explanation, based on rock-core evidence, for why petroleum is found at one site and not at another 200 kilometers away.
Read the scenario and the two core logs. A core log is a record of the rock a drill passes through, from the surface down. Answer the warm-up questions first; they organize the evidence. Then write your Claim, Evidence and Reasoning. A strong response names specific rock layers and depths from the logs and explains, step by step, the past processes that made oil at one site and made it impossible at the other.
You will need: This worksheet, Pencil, Scrap paper for the step list
An energy company drilled two exploration wells in the same state, about 200 kilometers apart. Site A is in the Harlow Basin, a region of low rolling hills. Site B is in the Kessler Highlands, a region of worn, rounded mountains. Both wells reached 3,000 meters, and the rock temperature at 2,500 meters was almost identical. Site A found oil; Site B found nothing. The company's board has asked for an explanation that a non-geologist can follow, and for a prediction about whether drilling deeper at Site B could ever succeed. The core logs below are simulated for this case, but every rock type and every clue in them is the kind geologists really use.
| Depth (m) | Rock | What the geologist noted |
|---|---|---|
| 0 - 300 | Loose river sand and gravel | Recent; fresh groundwater |
| 300 - 1,500 | Limestone | Fossil shells of sea creatures throughout; layers tilt gently, forming a broad arch under the drill site |
| 1,500 - 1,800 | Dense gray shale | No pores a liquid could pass through; same arch shape |
| 1,800 - 2,300 | Sandstone, porous | Pores filled with oil in the upper 120 m; below that, pores filled with salty water |
| 2,300 - 2,900 | Black shale | Microscopic fossils of ocean plankton; about 5 percent of the rock's mass is organic carbon; smells faintly of oil |
| 2,900 - 3,000 | Older sandstone | Water-filled; no oil |
| Depth (m) | Rock | What the geologist noted |
|---|---|---|
| 0 - 40 | Thin soil over weathered rock | Rocky, well drained |
| 40 - 2,100 | Granite | Crystallized from magma; no layers, no fossils, no pores a liquid could pass through except a few cracks |
| 2,100 - 3,000 | Gneiss (banded metamorphic rock) | Formed deep in the crust under great heat and pressure long before the granite; no fossils; organic carbon near zero |
Before writing, copy this list on scrap paper and fill in the depth from Site A's log next to each step: (1) ancient sea with plankton, buried in low-oxygen mud, becomes source rock: ______ m; (2) buried deep and heated so the organic matter turns to oil: temperature ______ °C at 2,500 m; (3) oil rises into porous reservoir rock: ______ m; (4) cap rock stops it and the arch traps it: ______ m. Now do the same for Site B and write 'none' wherever a step has no matching layer. Every blank you fill for Site A and every 'none' you write for Site B is a piece of evidence.
Oil companies use the four-step chain not only to explain but to search. Write three questions the company's board should ask before drilling a fourth well anywhere in the Harlow Basin, each tied to one step of the chain, and say what evidence (a rock type, a fossil, a temperature, a shape of the layers) would answer it. Then explain, in two sentences, why no amount of money could turn the Kessler Highlands into an oil field, and what that tells you about the difference between where a resource is wanted and where it is.