Abstract
The PC-C boundary interval represents one of the critical phases in the evolution of life. Any outside observer considering the approximately 4500-million-year history of our planet would likely choose the 150 Ma time interval between 650 and 500 Ma as one of the most dramatic periods in Earth history.
This period connects the Proterozoic and Phanerozoic Eons with its boundary at 542 Ma. It includes the Ediacaran (ca 630-542 Ma) and the Cambrian (542-493 Ma) periods.
The Ediacaran, in particular, is characterized by concurrent profound changes in global tectonics, possibly the largest climatic deviation from the steady-state mean global temperature since the Archean (popularized by the "Snowball Earth" concep), the first evidence leading to the possibly "explosive" (on a geological scale) but indisputably largest evolutionary radiation event of the biosphere, and a significant increase of free atmospheric and oceanic oxygen. The subsequent Cambrian time interval largely records the gradual establishment of a newly acquired ecologic stability, the beginning of the metazoan conquest of Earth's surface environment, and a profound rearrangement in the chemical composition of Earth's atmosphere and oceans.