Use this geological calculation for a transparent first-pass interpretation of measured rock, soil, fluid, well, stratigraphic, isotopic, geophysical, or seismic data under an explicitly selected model.

Radiogenic Ar-40

Radiogenic Ar-40 amount in the same units as potassium-40.

K-40

K-40 amount in the same units as radiogenic argon.

Compute a K-Ar age from radiogenic Ar-40 and K-40 amounts using the Steiger & Jager (1977) decay constants. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Age (yr)

K-Ar age in years.

Age (Ma)

K-Ar age in millions of years.

• Radiometric ages require the correct decay constants, isotopic ratios, standards, common-component correction, closure interpretation, initial composition, and analytical uncertainties. Disturbance, inheritance, diffusion, alteration, and model choice can make a calculated number differ from the geological event age.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Compare independent measurements and models, retain units and analytical metadata, propagate uncertainty, and validate interpretations against logs, cores, maps, laboratory data, or field observations.

• Geology Ar Ar Age Calculator

  Compute an Ar-40/Ar-39 age from the irradiation parameter J and the radiogenic Ar-40/Ar-39 ratio.

• Geology Lu Hf Isochron Calculator

  Fit a two-point Lu-Hf isochron and convert its slope to an age using the Lu-176 decay constant.

• Geology Rb Sr Isochron Calculator

  Fit a two-point Rb-Sr isochron and convert its slope to an age using the Rb-87 decay constant.