Distinguish dating evidence types

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or a browser document for a labeled drawing, table or explanation.
• Worked problem inputs: Layer A is below B, and a dated sample gives an interval for A. Distinguish the two conclusions.
• Assessment case 1: Layer A underlies B in an undisturbed stack, with no isotope date. What follows? Which inference or prediction is best supported?
• Assessment case 2: Which scientific label fits the specifically described step or feature? Supplied case: Measurement reports an age range in years.
• Assessment case 3: Which scientific label fits the specifically described step or feature? Supplied case: Two sites share an identified marker layer.
• Assessment case 4: Which scientific label fits the specifically described step or feature? Supplied case: Convergence builds mountains in model.
• Assessment case 5: Which scientific label fits the specifically described step or feature? Supplied case: Intrusion is younger than rock it cuts.
• Assessment case 6: A sample’s reported age is 50±3 million years under its dating model. What should the report preserve? Which inference or prediction is best supported?

Learn the idea

Relative dating orders events. Numerical dating estimates ages using suitable measurements and assumptions. Fossils can help correlate layers, while plate models explain movement and setting.

Relative order means which event came earlier. Numerical age means estimated age with a measured value. Correlation means matching units across locations. Tectonic explanation means mechanism involving plate movement.

For the supplied mechanism problem, Layer A is below B, and a dated sample gives an interval for A. Distinguish the two conclusions. Undisturbed order makes A relatively older than B. The dated sample provides a numerical age estimate for A with its stated uncertainty. Relative order alone does not provide an exact date.

1. Read the supplied problem and mark the structures, processes or quantities named: Layer A is below B, and a dated sample gives an interval for A. Distinguish the two conclusions.
2. Draw the relevant boundary, pathway or comparison and label it using the scientific ideas above.
3. Write a causal explanation or calculation, showing how each observation supports the result.
4. Compare your reasoning with the worked solution; name a condition that would change or limit the inference.

Check your reasoning

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Take it further

New case: a sample has numerical age 20±2 model million years while a layer below it is only relatively older. Expected: preserve the sample interval of 18–22 million years and distinguish it from the lower layer’s unspecified numerical age.

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