Life › Complex cells & first multicellular life
Ediacaran biota
c. 575–539 million years ago· Organism or group· Animals
Well establishedStrong fossil, genetic or geological evidence.
The first large, complex organisms, mostly soft-bodied seafloor life, known worldwide from about 575 to 539 million years ago.
See it on the Life map →What happened
Named for the Ediacara Hills of South Australia, where Reg Sprigg found them in 1946, they include fern-like fronds, quilted ovals like Dickinsonia, and possible mollusc relatives like Kimberella. Most lived on or in microbial mats in shallow and deep seas, and most were centimeters to a meter long. The oldest large assemblages, at Mistaken Point, Newfoundland, are roughly 570 million years old. Many disappear near the start of the Cambrian.
Why it matters
They show large multicellular life and early animals before the Cambrian, and they gave their name to the Ediacaran Period, adopted in 2004.
The evidence (fossils, genes, rocks)
Impressions in sandstone and volcanic ash beds in Australia, Newfoundland, Russia's White Sea coast, Namibia and England, dated by uranium-lead ages of ash layers.
Still debated
Many shapes, like the fronds, have no living relatives. Whether most were animals, and why they faded at the Cambrian boundary, remain debated.
Inside this (3)
Connections (4)
▸Snowball Earth was followed by Ediacaran biotaStrong evidence
The connection
Large Ediacaran organisms appear within about 60 million years of the last Snowball glaciation. The thaw left warmer seas, altered nutrient supply and possibly more oxygen, and the Ediacaran Period itself is defined as beginning at the end of the Marinoan glaciation, 635 million years ago.
When and how
Oceans worldwide, from about 635 to 575 million years ago; the period's starting point is marked at a cap carbonate in South Australia's Flinders Ranges.
How sure are we?
The sequence of events is well dated by uranium-lead ages; the causal link is inferred from timing and chemistry, not proved.
Debates and open questions
Did the glaciations help trigger complex life, or did life recover on its own schedule? A later ice age, the Gaskiers about 580 million years ago, complicates things.
▸Neoproterozoic Oxygenation Event supplied oxygen for Ediacaran biotaDebated
The connection
Large organisms need more oxygen than microbes, because oxygen must diffuse into bigger bodies. Rising oxygen in shallow and deep seas may have allowed Ediacaran organisms to reach meter scale and live on deep seafloors such as Mistaken Point.
When and how
About 580–539 million years ago; Don Canfield and colleagues linked deep-ocean oxygenation to the Newfoundland fossils in 2007.
How sure are we?
Iron chemistry in Newfoundland sediments suggests deep water became oxygenated after the Gaskiers glaciation, shortly before large fossils appear there.
Debates and open questions
Oxygen seems to have swung up and down; some argue Ediacaran organisms needed little oxygen and other factors mattered more.
▸Ediacaran biota includes DickinsoniaWell established
The connection
Dickinsonia is one of the best-known members of the Ediacaran biota, with thousands of specimens. Like many of its neighbors it lived on microbial mats and had a quilted, segmented-looking body, which makes it a key test case for what the Ediacaran organisms were.
When and how
Ediacara Hills, South Australia, where Reg Sprigg named it in 1947, and the White Sea coast of Russia, about 560–550 million years ago.
The evidence
It occurs in the same fossil beds as fronds and other Ediacaran forms, preserved in the same way.
Debates and open questions
Whether other quilted Ediacaran forms were also animals; Dickinsonia's result does not settle the identity of fronds such as Charnia.
▸Ediacaran biota gave way to Cambrian explosionStrong evidence
The connection
The Ediacaran world of mat-dwellers and fronds gave way, around 539 million years ago, to Cambrian animals that burrowed deeply, swam and hunted. Burrowing broke up the microbial mats, many Ediacaran forms disappeared, and some animal lineages carried on and diversified.
When and how
Near the Ediacaran–Cambrian boundary, about 539 million years ago; rocks in Namibia preserve both worlds in close succession.
How sure are we?
Dated rock sequences show Ediacaran forms dwindling as burrows and shells increase; a few Ediacaran-type fossils occur in Cambrian rocks.
Debates and open questions
Did Ediacaran organisms die in a mass extinction, get pushed out by Cambrian animals, or simply stop being preserved?