As originally envisioned, this concluding Chapter of Part 1 this monographic work was intended to be a multi-authored, collaborative effort prepared by participants in the Precambrian Paleobiology Research Group (PPRG) that would present a consensus view of the timing and nature of major events in the history of Proterozoic life. However, because of time constraints – at the time of the writing of this Chapter, it has already been more than two years since the end of the data gathering stage of the project – this initial plan had to be abandoned. Moreover, even without such constraints, uncertainities in the available data are such that competing and, in some cases, mutually inconsistent interpretations can be reasonably entertained regarding a number of major aspects of Proterozoic history; it is probably too early in the development of the field for unanimity of opinion to be attained. This, of course, is not necessarily deleterious: the field is young, the data are limited, and important questions remain unanswered. At this stage in the development of the science, dogmatic adherence to one or another validly competing interpretation might well be a disservice, leading the field into a cul-de-sac by inhibiting fruitful lines of inquiry.

What follows, therefore, is an attempt to present a balanced discussion of the problems at hand. Embedded within any such discussion, however, are certain to be the assumptions, preferences, and biases of the author – for the science to progress, judgments must be made, commonly on the basis of limited evidence – and it is likely that not all will agree with the interpretations preferred here.