Overview
This lecture introduces archaeological dating methods, focusing on dating conventions, types of dating (relative and absolute), and specific examples crucial for establishing the age of archaeological finds.
Dating Conventions in Archaeology
- Archaeologists use three main dating conventions: BC/AD, BCE/CE, and BP (Before Present, calculated from 1950).
- BC means "Before Christ" and AD means "Anno Domini" ("in the year of the Lord").
- BCE/CE stands for "Before Common Era" and "Common Era," intended to be less ethnocentric.
- BP is "Before Present," with "Present" set at 1950, used for radiocarbon and similar dating.
- Common abbreviations: "c." (century), "kya" (thousand years ago), "mya" (million years ago).
Types of Dating Methods
- Direct dating: dates the actual object, feature, or stratum.
- Indirect dating: dates something based on its association with another datable item.
Relative Dating Methods
- Relative dating determines whether something is older or younger than something else but does not provide calendar dates.
- Stratigraphic sequencing uses stratigraphy and the Law of Superposition—deeper layers are generally older.
- Sequence comparison (cross dating) uses diagnostic artifacts, such as coins, to provide a "terminus post quem" (date after which).
- Seriation orders artifacts by style or frequency to show change over time.
- Stylistic seriation: arranges artifacts by similarities in style or form.
- Frequency seriation: uses popularity trends (battleship curve) to sequence artifacts or deposits.
- Limitations include mixed strata and curated or reused artifacts.
Absolute Dating Methods
- Assigns calendar age ranges, often using scientific techniques.
- Dendrochronology (tree-ring dating): counts growth rings in wood to date when the tree was cut; requires species-specific master chronologies and preserved wood.
- Obsidian hydration: measures water absorption on obsidian artifacts to estimate time since breakage; limited to about 8,000 years and dependent on material/environment.
- Radiometric methods use radioactive decay:
- Radiocarbon (C-14) dating: dates organic materials between 500 and 50,000 years old; uses BP and is limited to uncontaminated, well-contexted samples.
- AMS (Accelerator Mass Spectrometry): a refined C-14 method that requires smaller samples and can date up to 100,000 years, still limited to organics and susceptible to contamination.
- Potassium-argon (K-Ar) dating: dates volcanic sediments older than 100,000 years; useful for dating layers, not artifacts, with a long half-life for potassium-40.
Key Terms & Definitions
- Direct Dating — dating the actual item of interest.
- Indirect Dating — dating based on association with other items.
- Relative Dating — establishes sequence/order, not actual dates.
- Absolute Dating — provides actual calendar dates or ranges.
- Law of Superposition — deeper layers are generally older.
- Terminus Post Quem — "date after which"; the youngest possible age of a stratum.
- Seriation — ordering artifacts in a sequence by style or frequency.
- Dendrochronology — tree-ring dating method.
- Obsidian Hydration — dating obsidian by measuring hydration layer.
- Radiocarbon Dating — measuring C-14 decay in organics.
- Accelerator Mass Spectrometry (AMS) — advanced C-14 dating method.
- Potassium-Argon Dating — dating volcanic sediments via K-40 decay.
Action Items / Next Steps
- Keep up with assigned readings.
- Complete all course activities before posted due dates.
- Contact instructor or TAs with questions.