LIFE × EXTINCTIONS

The End of the Ediacara Biota

~550 to 539 million years ago

Proterozoic · Neoproterozoic · Ediacaran

The fronds, discs and quilted bodies that had held the seafloor for thirty million years disappear, and the fossils suggest two steps rather than one: the first at the change of community around 550 million years ago, the second at the Cambrian boundary itself. Three explanations compete. They were killed; they were displaced by the new burrowing animals, which destroyed the microbial mats the older forms lived on; or only the rare conditions that preserved soft bodies came to an end, and the animals faded from view without dying out.

Why it matters

Large complex life had never been in trouble before. And the second explanation now has a measurement behind it: burrowing and sediment reworking rise sharply in the final few million years of the Ediacaran, well before the Cambrian begins. On that reading, nothing killed the Ediacarans. Something moved in and made their world uninhabitable.

Dating & uncertaintyDisputed

The fossils are too sparse to decide between the three readings, and the choice changes what the boundary means: a world emptied by a crisis, a world remade by its new occupants, or a Cheshire Cat, in which what disappears is the rare window that preserved soft bodies and not the animals themselves. Recent work argues for two pulses of loss rather than one.

Sources

1. Laflamme et al. (2013), Gondwana Research · The end of the Ediacara biota: extinction, biotic replacement, or Cheshire Cat?
2. Darroch et al. (2018), Trends in Ecology & Evolution · Ediacaran extinction and Cambrian explosion
3. Cribb et al. (2019), Royal Society Open Science · Increase in metazoan ecosystem engineering prior to the Ediacaran-Cambrian boundary in the Nama Group, Namibia

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