SCIENCE · INVESTIGATE AND EXPLAIN

Bound missing time without assigning it all to erosion

An unconformity records a break in the preserved sedimentary sequence. Nondeposition, erosion and removal of previously deposited material can contribute to the gap. An angular unconformity also records tilting before younger deposition; a disconformity separates sedimentary packages without necessarily changing their orientation, while a nonconformity overlies older crystalline rock.

Learning outcome: Reconstruct minimum and maximum gaps from the four displayed endpoints at two uncertainty settings. Draw a history that splits the missing time between nondeposition and erosion. Explain which additional marker would tighten the bound without proving a unique process duration.

Starting recap

Distinguish present position, relative event order, numerical age and duration. Preserve calibrated ranges, clock assumptions and missing observations instead of forcing one history.

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Try

For a=2 and b=3 Myr, older ages span 78–82 Ma and younger 57–63 Ma. The elapsed marker gap is 78−63=15 Myr at minimum and 82−57=25 Myr at maximum. Retaining all four endpoints prevents a mistaken subtraction of uncertainty widths.

Open the experiment

Predict

Will wider marker-age intervals always imply a longer minimum gap?

Your prediction and reason

Experiment

Reconstruct minimum and maximum gaps from the four displayed endpoints at two uncertainty settings. Draw a history that splits the missing time between nondeposition and erosion. Explain which additional marker would tighten the bound without proving a unique process duration.

Propagate age bounds without equating all missing time with erosion

Worked teaching model · synthetic values · Invented dated lower/upper marker bounds80±a and60±b Ma bracketing a missing interval. Independent stated hard bounds, not Gaussian uncertainties. Subtract youngest possible older bound and oldest possible younger bound for minimum gap; these markers need not coincide exactly with erosion start/end.

Older bound half-width: 2 Myr Younger bound half-width: 3 Myr

Reset keeps your prediction, captures and practice history.

A dated gap constrains elapsed time but does not assign all of it to active erosion.

Nondeposition, erosion and unrecorded deposition can share the interval. Marker ages that bracket an unconformity need not date its exact start and end; uncertain event interpretation is separate from numerical age uncertainty.

Complete conditional quantities
Quantity	Value	Unit
Older marker youngest bound	78	Ma
Older marker oldest bound	82	Ma
Younger marker youngest bound	57	Ma
Younger marker oldest bound	63	Ma
Minimum marker-to-marker elapsed gap	15	Myr
Maximum marker-to-marker elapsed gap	25	Myr

These are invented observation packets and calculations, not mapped field records or laboratory isotope measurements. Retain the source assumptions and first reasoning separately from public feedback.

A dated gap constrains elapsed time but does not assign all of it to active erosion.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

1. Define the time interpretation

2. Connect observations, mechanism and assumptions

The invented packet brackets a missing interval with an older marker at 80±a Ma and a younger marker at 60±b Ma. Here ± denotes a supplied hard interval, not a standard deviation. Ma is an age before present; Myr is an elapsed duration. Larger numerical ages are older.

The smallest marker-to-marker duration subtracts the oldest possible younger marker from the youngest possible older marker: (80−a)−(60+b). The largest duration is (80+a)−(60−b). These are conservative endpoint bounds with no probability model.

The markers need not coincide with the start and end of erosion. Therefore even an exact marker-to-marker duration does not prove that erosion lasted continuously for that whole time. Interpret the physical surface and depositional contacts separately from the numerical age uncertainties.

3. Reconstruct the worked packet

4. Predict and investigate

Predict first: Will wider marker-age intervals always imply a longer minimum gap?

5. Test a changed case

Apply the evidence to a changed case

If the older marker is 80±1 Ma and younger 60±4 Ma, give the possible elapsed interval and its interpretation.

Retain the chronology, calculations and assumptions before opening public feedback.

Compare a worked response

The interval is(79−64) to(81−56), or 15–25 Myr. It bounds marker separation, not necessarily the duration of continuous erosion.

6. Retain a defensible observation notebook

Preserve the original prediction, complete observations/relationships, calculations, uncertainty convention and rejected alternative. All sections and isotope packets here are invented instructional cases, not actual mapped outcrops or measured isotope analyses. Public practice is not independent reasoning review or supervised field competence.

Method and mechanism reference, checked 30 October 2026. Original prose, diagrams, numerical packets and exercises.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

If the older marker is 80±1 Ma and younger 60±4 Ma, give the possible elapsed interval and its interpretation.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Reconstruct all histories consistent with a cross-cutting packet Next: Combine calibrated fossil ranges without ignoring conflicting evidence

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