Skip to content

Lecture 6 — Archaeological Dating: Relative vs Absolute Chronologies

Big idea: Dating builds chronological sequences so archaeologists can explain change (cause/sequence). Methods are relative (older/younger) or absolute (calendar years, with uncertainty).

Why dating matters

  • Dating is difficult and frequently revised.
  • Accurate chronologies establish temporal sequences → enable causal explanations (“who was where when, and why?”).

Relative dating (older/younger than…)

1) Stratigraphy

What to examine:

  • position in profile,
  • relationships between layers,
  • internal composition (deposition speed; anthropogenic vs natural),
  • scale matters.

Special case:

  • Tephrochronology: volcanic ash layers as time markers.
  • “Basket loading” (dumping baskets of soil in construction) can create visible micro‑strata.

2) Seriation (stylistic / attribute‑based)

  • Style: recognizable manner of doing/making something; diagnostic of time/place (not only elites).
  • Seriation principle: order artifacts so adjacent items share more attributes than items far apart (“like with like”).

Assumptions:

  • culture changes in patterned ways,
  • material culture reflects those changes.

Pros: cheap, field‑usable, works when absolute methods don’t. Cons: no calendar years; depends on continuity and good sampling.

Absolute dating (calendar years, with error ranges)

Time scales / references

  • AD/BC and “neutralized” CE/BCE.
  • BP (Before Present) where “present” ≈ 1950 (standard in radiocarbon work).

1) Dendrochronology (tree‑ring dating)

  • Provides precise calendar dates.
  • Builds long sequences via cross‑dating (“matching barcodes”); now extends ~10,000 years in some regions.

Limitations:

  • species must have clear annual rings,
  • reuse/recycling can date wood growth, not construction (“old wood”),
  • preservation required.

2) Radiocarbon (¹⁴C) dating

Applies to:

  • organic (carbon‑based) materials.

Key limitations:

  • context/sample integrity,
  • “old wood” and reservoir effects,
  • effective to ~60,000 years (approximate upper bound),
  • results include uncertainty ranges.

Calibration (the big upgrade): Atmospheric ¹⁴C varies with solar activity, location, bomb carbon, fossil burning. Calibration uses known‑age materials (often tree rings) to convert radiocarbon years to calendar years.

Bayesian modeling: Combines stratigraphy/context constraints with ¹⁴C measurements to narrow ranges and improve chronological estimates.

3) Archaeomagnetic dating

  • Earth’s magnetic north moves.
  • Heating aligns iron particles; alignment “freezes” on cooling.
  • Date directly (artifact/feature) or indirectly (associated contexts).

4) Other radiometric methods (long half‑lives)

  • For rocks/sediments (not organics): uranium‑series, potassium‑argon, fission track, etc.

Direct vs indirect dating

  • Direct: date the object/feature itself.
  • Indirect: date by association with something directly dated (requires strong contextual linkage).