Complex Life May Have Existed on Earth Much Earlier Than We Thought

Exciting new evidence from an ancient sea in Africa.

Suspected traces of a tunneling organism, 2.1 billion years ago. (El Albani et al., PNAS)
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A new paper published in the Proceedings of the National Academy of Sciences by Abderrazak El Albani from the University of Poitiers in France and colleagues may lead paleontologists to rewrite the timeline of Earth’s natural history.

The research team analyzed the fossilized remains of a 2.1 billion-year-old, oxygenated shallow marine environment, now located in southeastern Gabon in West Africa. Tunnel structures discovered in the sediment—up to six millimeters in diameter and 170 mm in length—imply that some kind of slug-kind organism moved vertically and laterally through the sediment as it was still compacting. If so, the creatures may have fed on microbial mats.

Although the authors used modern tools including micro-CT scans, they could not say for certain whether the tunnels were created by a multicellular organism. The mucus trail left behind by the creature is reminiscent of today’s slime molds, but are much larger. Based on the organism’s motility—its ability to move independently using metabolic energy—and its apparent lifestyle of preying on other living things, it appears to have been astonishingly complex.

That’s not how we’ve come to think life on Earth evolved. The so-called Cambrian Explosion, the period in which most major animal phyla appear in the fossil record, happened 1.5 billion years after these tunneling creatures existed! The first animals on our planet, no more than a billion years ago, were assumed to be immobile filter feeders such as sponges, with passive lifestyles. In fact, eukaryotes—the first sophisticated microbes with a cell nucleus—didn’t even appear until 1.8 billion years ago, according to current thinking.

These newly found structures, produced by a macroscopic organism, predate both. If the findings by El Albani and colleagues are confirmed by later studies, it means that complex, possibly multicellular organisms evolved much earlier than previously thought.

There is another possible interpretation, even more exciting in my view. These organisms may be linked to the aftermath of the Great Oxidation Event, when oxygen levels on Earth rose above nearly oxygen-free background values for the first time in Earth’s history. The existence of these organisms, and complex life in general, could therefore be linked to the amount of oxygen present during that relatively brief period. And they may have disappeared when the level of oxygen declined again.

Either way, biological complexity appears to have occurred much easier and faster than we thought. And if the latter interpretation is correct, it may have arisen several times before it finally succeeded for good, and complex, macroscopic life forms took over the planet. This would be in line with what the Cosmic Zoo hypothesis predicts—that there are many paths to complex life, and that it could have been “invented” many times over.

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