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Eritrea for mobile viewing Science: A 558-Million-Year-Old Mystery Has Been Solved

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Date: Thursday, 20 September 2018

A Dickinsonia fossil
A Dickinsonia fossilIlya Bobrovskiy / Australian National University

Around 558 million years ago, a strange … something dies on the floor of an ancient ocean. Its body, if you could call it that, is a two-inch-long oval with symmetric ribs running from its midline to its fringes. It is quickly buried in sediment, and gradually turns into a fossil.

While it sits in place, petrifying, waiting, the world around it changes. The Earth’s landmasses merge into a single supercontinent before going their separate ways. In the ocean, animal life explodes; for the first time, the world is home to eyes, shells, and mouths. Living things invade the land, coating it first in thin films of moss and lichens, and then covering it in huge forests. Insects rise, into existence, and then into the skies. A dinosaur empire rises and falls. Mammals finally take over, and one of them—a human by the name of Ilya Bobrovskiy—finally unearths the fossilized ribbed oval from its resting place.

All of which is to say: Five hundred fifty-eight million years is an incredibly long time.

But despite that almost unimaginable time span, and everything that happened within it, many of the simple molecules that once existed in the oval creature’s cells still persist. Bobrovskiy, a geochemist at Australian National University, has isolated, identified, and measured them. And they provide conclusive evidence that the creature, despite all appearances, is an animal. More specifically, it is the oldest animal ever discovered. It’s called Dickinsonia.

Ilya Bobrovskiy / Australian National University

First discovered in the 1940s, Dickinsonia is one of the most iconic members of the so-called Ediacaran biota—a group of mysterious, soft-bodied organisms that existed between 541 and 570 million years ago. In a world that had been dominated by microbes, these were the first big, complex living things. They would have been visible to the naked eye, had eyes even existed at that point.

But what were they? Some looked like tall fronds; others, such as Dickinsonia, were flat mats. They were so unlike the animals, plants, and other organisms we know today that one scientist described them as “strange as life on another planet, but easier to reach.” Some paleontologists, including Dickinsonia’s original discoverer, classified them as animals, precursors to the more familiar forms that arose later, during the Cambrian explosion. Others have taken them for giant amoebalike protists, lichens, colonies of bacteria, or even a completely extinct kingdom of life.

Bobrovskiy recently came up with a new way of resolving these debates. While looking at Ediacaran fossils under a microscope, he noticed distinctive dark films. These were the unmistakable signs of organic compounds that had been left behind when their owners’ bodies had decayed. Large, complicated molecules such as DNA or proteins don’t survive long after an organism’s death, but smaller and more stable molecules can. If Bobrovskiy could recover them, he could look for distinctive chemical signatures that distinguish animals from bacteria and other kingdoms of life. “[My supervisor] Jochen [Brocks] said we could try it, but he was always sure that it was a stupid idea,” Bobrovskiy says. “Even I thought it would fail. But it didn’t.”

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