Skip to content
LITHOEN

Isotope

Potassium-40

A rare radioactive isotope of potassium that is simultaneously a geological clock and one of the three principal sources of Earth’s radiogenic heat.

Classification

element symbol
K
mass number
40
stability
radioactive

How this record is known

1
Directly recorded
Observed or measured, reported by the party that made the observation.
1
Settled consensus
Cited as the accepted position of the discipline.

2 of 2 claims on this page cite at least one registered source. Counts describe how each statement is known, not how likely it is to be true.

What Lithoen records

Each claim states how it is known and cites its evidence.

Measured0.000117 ratio

Potassium-40 makes up 0.000117 of natural potassium — about one atom in eight and a half thousand — yet that trace is one of the three principal sources of Earth’s radiogenic heat and the basis of potassium–argon dating.

  • method: CIAAW critical evaluation; the published value carries an uncertainty of 1 in the last digit.
  • precision note: A single value rather than an interval: potassium’s isotopic composition does not vary appreciably between normal materials.

Evidence support: Supported by the cited evidence one source

Evidence: Commission on Isotopic Abundances and Atomic Weights (IUPAC) 2024 Primary authority

In the knowledge graph

Record last updated 2026-09-06. Corrections follow the published corrections policy; superseded claims are retained, never silently edited.