In 1960, John Reynolds (Univ. Cal. Berkeley) published results of an experiment in which he had fused a 7g sample of a primitive meteorite, the Richardton carbonaceous chondrite, in a vacuum and analyzed its Xe isotopic composition.

He compared the abundances of its Xe isotopes with that found in the atmosphere and found that the abundance of the isotope 129Xe was enhanced relative to atmospheric Xe in the meteorite sample.

Reynolds I-Xe

Terrestrial Xe composition shown by marks. Reynolds argued that the excess 129Xe was a daughter product from the radioactive decay of 129I within the meteorite sample.

I-Xe decay scheme

Reynolds also argued that this evidence indicated that the chemical elements that make up our solar system were synthesised only shortly before formation of the solar system, that there was live 129I present when solar system formed and that the radioactive 129I was incorporated into the Richardson meteorite when it formed.

This proposal was initially received somewhat sceptically but, with the identification of other short-lived radioactive decay products in meteorites (i.e. 26Mg from 26Al decay, 53Cr from 53Mn decay, 182W from 182Hf decay etc) is now widely accepted.