Around 40 million years before the Cambrian explosion, the young oceans born of Snowball Earth's thaw hosted a remarkable flourishing of organisms: the Ediacaran biota. First described from the Ediacara Hills of South Australia in 1946, these fossils are now identified in rocks from Russia to China, Namibia to Canada.

Ediacaran organisms were strikingly diverse, yet all were soft-bodied — no shells, bones, or mineralised skeletons. Among the best-documented, Dickinsonia lived on the seafloor across millions of years, ranging in body size from 1 mm to 1.4 metres. In 2018 researchers detected sterol biomarkers preserved in Dickinsonia fossils, placing it among the oldest confirmed animal-grade organisms — though its precise classification remains disputed. Charnia, superficially plant-like, lived in deep water below the photic zone, suggesting it was not photosynthetic and may be closer to an animal or fungal lineage.

The mystery of the Ediacaran biota extends to its ending as much as its identity. By the Cambrian boundary, most of these organisms had vanished, replaced rapidly by animals bearing shells, eyes, and jointed limbs. One interpretation holds that the entire Ediacaran assemblage represents an evolutionary dead end — a failed experiment in multicellularity. Another sees animal lineages rooting within this community. Recent trace fossil evidence points to actively moving, likely animal-grade organisms already present in the Ediacaran.

Whatever their true evolutionary affinities, the Ediacaran biota mark a threshold in the history of life: the first major rehearsal of the transition from a microscopic world to a multicellular, macroscopic, and visible biosphere.