For the first time since 1891, the geologic timescale is getting a new period. In March the International Union of Geological Scientists added the Ediacaran Period to the Precambrian Eon, an enormous time span that covers 90 percent of geologic history.
The new period takes its name from Ediacaran fossils, remains of the oldest-known complex animal life, that were found in abundance in the Ediacaran Hills of South Australia. The period begins around 620 million years ago with the rapid end of
the global Marinoan glaciation—a great environmental calamity that entombed the planet in ice for several million years. It ends 543 million years ago with the onset of the Cambrian Period and the explosion of animal life.
As geologists readily admit, the table has its shortcomings. While the most recent 543 million years—the Phanerozoic Eon—are heavily subdivided into three eras and 11 periods, the remaining 4.1 billion years are ...
