Archaeology Stratigraphy Lab
Archaeologists read a site by its layers. Dig down through the strata of a composite site, uncover the artifacts in each layer, estimate their ages from depth and a sedimentation rate, and build the chronology. Along the way, sort the clues into what was observed and what was inferred.
Guided Experiment: Which artifact is oldest and how do you know?
Before you dig, predict which artifact at the site will be the oldest. Explain how the position of a find in the layers tells you its relative age.
Write your hypothesis in the Lab Report panel, then click Next.
Rivermeadow Field cross section
Younger on top, older belowEach circle marks an artifact at its find depth. Deeper finds were buried earlier, so they are older by the law of superposition.
Controls
A composite riverside field where a town grew over an older farmstead and a much older campsite. Four layers from topsoil down to a buried hearth.
The depths are measured evidence. The estimated ages depend on this assumed rate, which is an interpretation. Change it and the ages shift, but the oldest first order does not.
Site chronology, oldest first
Ages use the assumed rate of 0.1 cm per year.
- 1Glass bottleTopsoil · 10 cm · Glass100 yr BPModern
The order here, the relative dating, is reliable because deeper layers were laid down first. The absolute ages are an interpretation that depends on the assumed sedimentation rate.
Evidence or interpretation?
Evidence is something the team directly observed or found. Interpretation is an idea inferred from that evidence. Tag each statement, then check your work.
A clay pot shard was found at 50 cm depth.
These people stored grain in large clay jars.
A layer of ash sits below the iron nails.
A cooking fire burned here before the town was built.
A bronze coin lay deeper than the glass bottle.
The coin shows this was a wealthy trading settlement.
Data Table
(0 rows)| # | Artifact | Layer | Depth (cm) | Estimated age (years BP) | Period |
|---|
Reference Guide
The Law of Superposition
In an undisturbed site, sediment piles up over time, so each new layer sits on top of the older ones. The deeper a layer, the earlier it was laid down.
That gives archaeologists a powerful rule. An artifact found in a deeper layer is older than one above it. You can order finds in time just from where they sit in the section, before you ever try to attach a calendar date.
The lab draws the section youngest on top and oldest below, with each artifact marked at its find depth, so the chronology reads straight off the wall of the dig.
Relative and Absolute Dating
Relative dating puts events in order. Superposition tells you which artifact is older without giving a year. That ordering is reliable as long as the layers are undisturbed.
Absolute dating tries to attach an actual age. In this lab a simple estimate divides the depth by an assumed sedimentation rate. Change the rate and every age shifts, but the order of the artifacts stays the same.
Real archaeology uses methods like radiocarbon dating for absolute ages. The lesson here is the same. The order is firm, while any single number depends on an assumption.
Evidence and Interpretation
Evidence is what the team directly observed. A clay pot shard at 50 cm depth is evidence, because someone found it and measured where it was.
Interpretation is the story we infer from that evidence. Saying the people stored grain in clay jars goes beyond the find. It may be a good idea, but it is a conclusion, not a raw observation.
Keeping the two apart is a core historical thinking skill. Strong conclusions name their evidence, admit where they interpret, and change when new finds come in.
