radiocarbon

radioactive isotope of the element carbon, ¹⁴C, having 8 neutrons, 6 protons, and 6 electrons

Note 1

Of the total carbon on Earth, 1 × 10⁻¹⁰ % is ¹⁴C. It decays exponentially with a half-life of 5 730 years and, as such, it is not measurable in fossil materials derived from petroleum, coal, natural gas, or any other source older than about 50 000 years.