LIFE × EXTINCTIONS

The End of the Ediacara Biota

~550 to 539 million years ago

Proterozoic · Neoproterozoic · Ediacaran

The end of the Ediacara biota is the disappearance in two steps, between 550 and 539 million years ago, of the fronds, discs and quilted bodies of this seafloor community.

The Ediacara biota is the community of fronds, discs and quilted bodies, with a padded and segmented surface, that had occupied the seafloor for thirty million years. The fossil record, the fossils preserved in rock, indicates that it disappeared in two steps rather than one. The first falls around 550 million years ago, at a change of assemblage, when one group of fossil forms replaces another. The second falls at the Cambrian boundary, the start of the Cambrian period. Researchers propose three explanations. In the first, an environmental event killed the organisms. In the second, new burrowing animals displaced them by destroying the microbial mats, layers of microbes on the sediment, on which the older forms depended. This is ecosystem engineering: organisms transforming the environment of others. In the third, the rare conditions that permit Ediacara-type preservation of soft bodies ended, and the animals stopped being fossilised without becoming extinct.

Why it matters

Before this disappearance, large complex organisms had never been in difficulty. The explanation by burrowing animals now rests on a measurement. Cribb and colleagues (2019) show that burrowing and the reworking of sediment by animals increase markedly in the last few million years of the Ediacaran, the period before the Cambrian begins. On that reading, the Ediacaran organisms disappeared because new occupants made their environment uninhabitable.

Dating & uncertaintyDisputed

The fossils are too few to decide between the three explanations, and each gives a different meaning to the boundary between the Ediacaran and the Cambrian. In the first, the boundary marks a world emptied by a crisis. In the second, it marks a world transformed by its new occupants. In the third, it marks an erasure of the record, in which the rare conditions that preserved soft bodies disappear and not the animals themselves. Recent work argues for two phases of loss rather than one.

Earth history as one day

21:05:332 h 54 min before midnight

if Earth’s 4.54 billion years were compressed into a single day