What Is Radiocarbon Dating and How Does It Work?

Radiocarbon dating estimates the age of once-living material by measuring how much carbon-14 remains in a sample. It works because living things constantly absorb carbon from the atmosphere, and that intake stops at death, after which carbon-14 decays at a known rate. It applies to organic remains and some carbonates up to roughly 50,000 years old, and the practical accuracy depends heavily on sample type, sample size, and freedom from contamination. If your material is organic or carbonate-based and falls within that age range, radiocarbon dating is likely applicable; if it is older, inorganic (non-carbonate), or heavily contaminated, it is not.

The core mechanism: carbon-14 formation, uptake, and decay

Carbon-14 is produced in the upper atmosphere when cosmic rays interact with nitrogen. The resulting carbon-14 combines with oxygen to form carbon dioxide, which mixes into the atmosphere and enters the food chain through photosynthesis and feeding.

While an organism is alive, its carbon-14 level stays roughly in equilibrium with the atmosphere. When it dies, uptake stops and the carbon-14 already present begins to decay into nitrogen-14 at a fixed rate.

Half-life and the dating window

• Half-life: about 5,730 years. After one half-life, half the original carbon-14 remains; after two, a quarter; and so on.
• Practical limit: roughly 50,000 years. Beyond about 10 half-lives, too little carbon-14 remains to measure reliably, which is why radiocarbon dating cannot reach into the millions of years that other methods (such as potassium-argon) cover.

Because the decay rate is constant, measuring the remaining carbon-14 relative to stable carbon tells you how long decay has been running — that is, how long ago the organism died.

How the measurement is done: AMS vs. traditional methods

Two broad approaches exist, and they differ mainly in sensitivity and sample size.

AMS is more commonly used today because it can date much smaller samples and generally returns results faster. SGS Beta, for example, describes providing AMS dating results in 3–14 business days, which reflects the speed advantage of direct atom counting over waiting for decay events.

What samples can be dated

Radiocarbon dating applies to material that once exchanged carbon with the environment. Based on the laboratory's listed sample categories, common types include:

• Bones & teeth — datable via the organic (collagen) fraction
• Shell & other carbonates — datable because carbonate incorporates environmental carbon
• Plants & seeds — direct products of photosynthesis
• Wood — a classic and often reliable sample type

The key requirement is that the carbon in the sample is original to the organism and has not been replaced or contaminated since death.

Limits, calibration, and common pitfalls

Radiocarbon dating is not a simple "read the number" process. Several factors affect the result:

• Calibration: Atmospheric carbon-14 levels have varied over time, so raw "radiocarbon years" must be converted to calendar years using a calibration curve. An uncalibrated date is not a calendar date.
• Contamination: Even small amounts of younger or older carbon can shift results. Handling, storage, and pretreatment matter, which is why laboratories apply sample-specific preparation.
• Sample size: Traditional methods need larger samples; AMS reduces this requirement but does not eliminate it.
• Age ceiling: Samples near or beyond ~50,000 years yield "beyond limit" results rather than a precise age.
• Material suitability: Non-carbonate inorganic materials and samples with no original carbon cannot be dated by this method.

Deciding whether it fits your sample

Use these conditions to judge applicability:

• Yes, likely suitable: organic material (bone, tooth, shell, plant, seed, wood) with intact original carbon, within ~50,000 years, and enough material for the chosen method.
• No, not suitable: material older than the dating limit, non-carbonate inorganic material, or samples so contaminated that original carbon cannot be isolated.

If your sample is small or valuable, AMS is generally the better fit. If you are unsure, a laboratory's technical support can help match the sample to the right preparation and method — SGS Beta explicitly offers expert technical support for selecting the most suitable samples.