Annual Review of Earth and Planetary Sciences, 2019

This volume opens with an introductory article by Hoffmann, a renowned Precambrian geologist, wherein he explains the significance of the Proterozoic Eon (2.5–0.54 Ga). A neglected part of Earth’s history for long, this interval is defined by many important milestones in the evolutionary history of our planet. For example, it was during this time-period that plate tectonics took its modern form resulting in a supercontinent formation and its dispersion later. The early part of this interval also saw the development of eukaryotic cells, chloroplasts and sexual reproduction. The end of the Proterozoic Eon is marked by repeated build-up of glaciers covering the entire Earth’s surface, known in the literature as Snowball Earth. Hoffman’s article narrates these unprecedented happenings during this dramatic part of Earth’s history – that personally he likes to call this as a story of his ‘love affair’ with an eon.