Fossils: Absolute dating techniques

Absolute Dating

A quantitative dating method used to calculate the precise age of a specimen or surrounding rock in years before present time (BP).

Potassium-Argon (K-Ar) Dating

An absolute dating technique that measures the radioactive decay of Potassium-40 into Argon-40 in volcanic rock to infer the age of fossils buried within it.

Potassium-40 Half-Life

The constant rate of decay for K-40, which takes approximately 1.25 billion ($1.25 \times 10^9$) years for half of the isotope to decay into Argon-40 and Calcium-40.

K-Ar Dating Applications & Limitations

Suitable for dating volcanic rock samples older than 200,000 years (up to 4.3 billion years), but cannot be used on samples younger than 100,000–200,000 years due to undetectable levels of Argon-40.

Closed System Requirement

The assumption in K-Ar dating that no potassium or argon has been lost or gained by the rock since its formation.

Radiocarbon (Carbon-14) Dating

An absolute dating technique for organic material that measures the decay ratio of radioactive Carbon-14 to stable Carbon-12.

Carbon-14 Half-Life

The fixed decay rate of Carbon-14, taking 5,730 years for half of the isotope to decay into Nitrogen after an organism dies and stops absorbing carbon.

Carbon-14 Applications & Limitations

Used to date organic artifacts (like charcoal or bone) up to 60,000 years old, but unusable beyond 70,000 years as too little Carbon-14 remains to measure accurately.

Accelerator Mass Spectrometry (AMS)

An advanced form of radiocarbon dating that requires as little as 100 micrograms of sample, enabling the non-destructive dating of tiny artifacts like cave painting pigments.

Atmospheric Carbon Fluctuations

A key limitation of radiocarbon dating requiring calibration, based on the fact that the ratio of Carbon-14 to Carbon-12 in the atmosphere has varied over time rather than remaining constant.