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 in two steps: once at the change of community around 550 million years ago, and again at the Cambrian boundary itself. Three explanations compete. They were killed; they were displaced by the new burrowing animals, which destroyed the microbial mats they lived on; or only the rare conditions that preserved soft bodies went away, 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 has now been measured: burrowing and sediment reworking rise sharply in the last few million years of the Ediacaran, before the Cambrian begins. On that reading nothing killed the Ediacarans. Something moved in and made their world uninhabitable.

Dating & uncertaintyDisputed

Three readings compete and the fossils are too sparse to settle them: a genuine extinction; a replacement, with the new burrowing animals destroying the mats the Ediacarans lived on; or a Cheshire Cat, in which only the rare conditions that preserved soft bodies disappear. Most accounts now see two pulses 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