In Radiocarbon and Egyptian Dates you saw how radiocarbon checks the historical chronology. Here is how the method works, step by step, and what it can and cannot date.
Key idea
Why it works
| Half-lives passed | Fraction of carbon-14 left | Years (half-life 5,730) |
|---|---|---|
| 1 | 1/2 | 5,730 |
| 2 | 1/4 | 11,460 |
| 3 | 1/8 | 17,190 |
| about 0.8 | about 0.58 | about 4,500 (a sample from the pyramid age) |
Worked example: Counting half-lives
- 1/4 = 1/2 × 1/2, so two half-lives have passed.
- 2 × 5,730 = 11,460 years.
- That is far older than dynastic Egypt: it would come from a site of the last Ice Age, before farming.
Answer: About 11,460 years.
Worked example: A sample from the pyramid age
- Age ÷ half-life = 4,550 ÷ 5,730 ≈ 0.794.
- (1/2)^0.794 ≈ 0.577.
- So a little less than 3/5 of the carbon-14 remains: less than one half-life has passed.
Answer: About 0.58 (58%).
What it can date
- Yes: wood and charcoal, seeds and grain, reed, papyrus, linen, basketry, bone, hair, leather: anything once alive.
- No: stone, metal or the clay of a pot (though food residue or straw inside a pot may be datable).
- Care: wood can be much older than the building it was used in (a beam reused, or the inner rings of an old tree). Short-lived plants, like seeds and reeds, are best.
The first test of the method, by Willard Libby and James Arnold in 1949, used wood from the tombs of Djoser and Sneferu, whose age was known from history. In 2010 a team led by Christopher Bronk Ramsey dated 211 short-lived plant samples from museum collections, tied to particular reigns; the results agreed well with the standard historical chronology and placed the start of the New Kingdom in the range c. 1570–1544 BC.
Common mistake