 The Proterozoic Eon also featured the first definitive supercontinent cycles and wholly modern mountain building activity (orogeny).There is evidence that the first known glaciations occurred during the Proterozoic.The first began shortly after the beginning of the Proterozoic Eon, and evidence of at least four during the Neoproterozoic Era at the end of the Proterozoic Eon, possibly climaxing with the hypothesized Snowball Earth of the Sturtian and Marinoan glaciations.