If you studied natural history years ago, you learned a fascinating tale of a microbe dominated primeval earth. In this story, one-celled critters swarmed in primeval oceans, blissfully free of larger predators, for billions of years. Then along came snowball earth, followed by the blooming Cambrian Explosion over half a billion years ago that changed everything.

Shallow oceans were suddenly teeming with giant flesh-eating shrimp like the Anomalocaris, snails armored in chain-mail, and other predators of tentacle and chitin patrolling a bizarre watery sea bottom populated with strange frond-like animals, mud-sucking hallucigenia, and of course everyone's favorite Cambrian critter, trilobites. It's a great story. It is also, as we're learning lately, more and more debatable:

The discovery in Gabon of more than 250 fossils in an excellent state of conservation has provided proof, for the first time, of the existence of multicellular organisms 2.1 billion years ago. This finding represents a major breakthrough: until now, the first complex life forms (made up of several cells) dated from around 600 million years ago.

It's not clear exactly what these are, or were. Plants, animals, or do those modern distinctions even apply? They may be cousins of later trisymmetrical biota that have no living analogue today. Or they could be related to modern day Xenophyphora which would still make them one-celled creatures, just exceptionally large ones. They could also represent something like a primitive Cnidaria.

Cue the "Scientists Stunned" headlines -- and forgive me for my own spin on that old trope above. Paleobiologists have long suspected, and recent fossil evidence strongly suggests, that the Cambrian Explosion is more an artifact of random fossilization and geology than the Start of Life as We Sort of Know It. Most ancient ocean strata laid down that long ago has disappeared under the grinding edge of tectonic plates, or been eroded away into dust by wave after wave of advancing glacier. Much of what gave rise to the idea of the classic explosion decades ago comes from a single small site of rare, fossil bearing marine sediment in Canada that preserved a snapshot of Cambrian plants and animals in exquisite detail. Newer discoveries have since pushed the likely start of complex life back over a hundred million years. But that headline hype might, for once, actually apply assuming this holds up: two billion year-old multicellular critters are pretty surprising.

Cross-posted from the Examiner.com by popular demand.