On a hillside just west of the Flinders Ranges, geologist Mary Droser lounges casually on a slab of 550-million-year-old sandstone. The sun has just hit its golden afternoon angle; it illuminates squiggled lines in the rocks, throwing into sharp contrast some of the earliest evidence for animal life on the planet.
“This guy here is a burrow, made by an animal moving through the sediment,” Droser tells me, tracing her finger over the lines.
This creature must have been moving with purpose and direction along the ancient sea floor, shifting thin layers of sand to form burrows that are now frozen in time. “Head, way in, way out, through-gut, able to move, muscles,” she muses. “A lot of things go into the organism that can do this.”
These burrows are of particular interest to Droser and her team. For a long time, they only had the burrows; the tiny creature that created them was elusive. Then Droser got her hands on a 3D laser scanner to investigate minuscule blobs found nearby, and discovered the impressions of a simple, worm-like animal half the size of a grain of rice.
This critter, Ikaria wariootia, marked a breakthrough in our understanding of life on Earth, becoming one of the oldest known animal fossils. “This had to have been an animal,” Droser says. “That was a champagne moment for us.”
This hillside we’re sitting on is part of the new Nilpena Ediacara National Park, on an old cattle station 600 dusty kilometres north of Adelaide. Today, these slopes are covered in loose rocks and scrubby vegetation, but half a billion years ago they were at the bottom of a calm, shallow, tropical sea.
HOW DO WE SEARCH FOR AN ANIMAL THAT LIVED MORE THAN HALF A BILLION YEARS AGO?
The world had recently undergone a crucial transformation: as the planet emerged from an ice age that stretched from poles to equator, the atmosphere warmed and oxygen levels soared. Sometime in this period, single-celled life tumbled into multicellular creatures and gave