Complex sentence: Of the thirty-seven known isotopes of iodine, only one occurs in nature, the stable iodine-127: all the others are radioactive and have half-lives too short to be primordial.
Split into simpler sentences: Of the thirty-seven known isotopes of iodine, only one occurs in nature, iodine-127. The others are radioactive and have half-lives too short to be primordial.