Concept · Ch 2
The Ediacaran dawn
In 1946 a geologist found faint, coin-shaped impressions in rock north of Adelaide — the first solid proof that large, complex animal life existed before the Cambrian, and the discovery that gave the world's newest geological period its name.
First, meet: The Adelaide RiftSnowball Earth (the Sturtian & Marinoan glaciations)
Every so often a landscape hands over a fact so large it changes what every textbook on Earth has to say, and Adelaide’s back country has done it at least once. In 1946 a young geologist named Reg Sprigg was sent to check on some abandoned mine workings in the Ediacara Hills, a few hundred kilometres north of the city but part of the same rift system that built the ranges behind it. Turning over slabs of ancient sandstone, he noticed faint, coin-like impressions pressed into the rock — not shells, not bones, but the ghostly outlines of soft, quilted creatures with no obvious mouths, guts or limbs.
He got the story half right and the world ignored the rest. Sprigg wrote the fossils up as “Early Cambrian (?) jellyfishes” (Sprigg 1947), submitted a paper to Nature that was rejected, and gave a talk in London the following year that barely raised an eyebrow. The trouble was that his fossils were older than anyone had been trained to believe animal life could be. It took another decade and two more scientists, Martin Glaessner and Mary Wade at the University of Adelaide, patiently working the beds through the 1950s and 60s, to show the impressions were Precambrian: proof that big, complicated organisms existed tens of millions of years before the “Cambrian explosion” was supposed to have invented them from scratch.
The names these creatures carry are half the pleasure of meeting them: Dickinsonia, a ribbed oval like a bathmat with ambitions; Spriggina, honouring its finder; Parvancorina, the “little anchor”; Tribrachidium, built to a three-fold symmetry nothing alive today shares. What they actually were is still argued over — jellyfish, worms, or something with no living relatives at all — though in 2018 a molecular trace of cholesterol lifted from a Russian Dickinsonia at least confirmed that one of them was, biochemically, an animal.
The fossils mattered enough to reshape the calendar itself. In 2004 geologists ratified an entirely new period of Earth history built around this find — the Ediacaran, the first new period declared in more than a century, its formal starting line fixed in the Flinders Ranges. Stand at Sturt Gorge or drive the range-front road today and you are walking the same rift system that, a few hundred kilometres north, quietly rewrote the opening chapter of animal life.
Go deeper — the mechanism & the evidence
The discovery took decades to be believed for a reason: it broke a rule geologists had trusted for a century, that complex animal life began abruptly with the Cambrian "explosion." Sprigg's 1946 finds in the Ediacara Hills were fossil impressions in the Ediacara Member of the Rawnsley Quartzite, but he first read them, in print, as "Early Cambrian (?) jellyfishes" (Sprigg 1947) — the right rock, the wrong era. It took Martin Glaessner and Mary Wade, working through the 1950s and 60s, to establish that the beds sat well below the Cambrian boundary and that the fauna was genuinely Precambrian (Vickers-Rich 2007) — old enough that the whole animal kingdom had to be pushed back in time to make room for it. The rocks eventually gave the geological timescale its own new period, the Ediacaran, formally ratified in 2004 with its boundary fixed at Enorama Creek in the Flinders Ranges — the first new period declared in more than a century, and still the only one with its global reference point in the Southern Hemisphere (Knoll et al. 2006). What these soft-bodied creatures actually were remained a live argument until 2018, when Ilya Bobrovskiy's team found molecular traces of cholesterol — a fat only animals make — preserved in a Russian specimen of Dickinsonia, closing a seventy-year debate about at least one of them (Bobrovskiy et al. 2018).
Sources & further reading
Every claim here is traceable. Each citation links to its entry in the bibliography.
- Sprigg, R.C. (1947). Early Cambrian (?) jellyfishes from the Flinders Ranges, South Australia. Transactions of the Royal Society of South Australia 71:212–224. — Sprigg's original 1947 description of the Ediacara fossils as (misidentified) Cambrian jellyfish.
- Vickers-Rich, P. (2007). Sprigg, Glaessner and Wade and the discovery and international recognition of the Ediacaran fauna. Geological Society, London, Special Publications 286:405–412. https://doi.org/10.1144/SP286.37 — How Glaessner and Wade established the fauna's true Precambrian age and significance.
- Knoll, A.H., Walter, M.R., Narbonne, G.M. & Christie-Blick, N. (2006). The Ediacaran Period: a new addition to the geologic time scale. Lethaia 39(1): 13–30. DOI: 10.1080/00241160500409223. https://onlinelibrary.wiley.com/doi/10.1080/00241160500409223 — The Ediacaran ratified as a new geological period, GSSP at Enorama Creek.
- Bobrovskiy, I., Hope, J.M., Ivantsov, A., Nettersheim, B.J., Hallmann, C. & Brocks, J.J. (2018). Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals. Science 361(6408):1246–1249. https://doi.org/10.1126/science.aat7228 — Cholesterol biomarkers in Dickinsonia settle its identity as an animal.
See it in the country
Grounded in A Coast Running Out of Water. Every figure is stated once in the book's canonical facts register and cited to a published source.