Given the half-life of 244Pu, an exceedingly small amount should still be present on Earth, making plutonium a likely but unproven candidate as the shortest-lived primordial element.

Considering the likely abundance ratio of 244Pu to 238U in the early solar system (~0.008), this upper limit is still 18x greater than the expected present 244Pu content in the bastnasite sample (1.2×10−21 g/g).

[5] Trace amounts of 244Pu (that arrived on Earth within the last 10 million years) were found in rock from the Pacific ocean by a Japanese oil exploration company.

[7] It is important to recall, however, that in order to be a primordial nuclide – one constituting the amalgam orbiting the Sun that ultimately coalesced into the Earth – plutonium-244 must have comprised some of the solar nebula, rather than having been replenished by extrasolar meteoritic dust.

[10] Radionuclides such as 244Pu, decay to produce fissiogenic (i.e., arising from fission) xenon isotopes that can then be used to time the events of the early Solar System.

Examination of a whitlockite crystal within a lunar rock specimen brought by Apollo 14, established proportions of Pu/U fission tracks consistent with the (Pu/U)0 time dependence.