Robyn Williams: And so to Ella Finkel, writer, former editor of Cosmos magazine, still writing for it with news you should enjoy.

Ella Finkel: Dear Science Show devotees, I'm going to give you a reason to rejoice. One of Australia's most important national parks has just increased in size by over tenfold. Ediacara Conservation Park ballooned by acquiring half of Nilpena cattle station, an 800 square kilometre semiarid pastureland on the western outskirts of South Australia's Flinders Ranges. Why is this park so important? It's the first step in acquiring world heritage status and everlasting protection of the most enigmatic fossils on our planet, the Ediacarans. They might just hold the answer to Darwin's dilemma.

For protecting the fossils until now, we have to thank Nilpena's owner, fourth generation pastoralist Ross Fargher. He found the fossils on a hillside while mustering 30 years ago. Then he defied the museum boffins who wanted to cart them away. In his bones, he felt it was important to study the fossils just where they lay.

Last year his three decades of policing the fossils and helping scientists carry out their research was recognised with an award from the American Palaeontological Society. But Ross couldn't protect the fossils forever, which is why the South Australian government just purchased half of his New York City-sized cattle station.

So why does Nilpena hold the key to Darwin's dilemma? Let's scoot back to 1859 and the publication of Origin of Species. It was Darwin's attempt to answer the 'mystery of mysteries'. Namely, Earth's rock layers showed new species emerging over time, but where did they come from? From ancestors, argued Darwin. The argument worked fine until you got to the very oldest fossils: those in 541-million-year-old Cambrian rocks.

Most of the basic animal models or 'phyla' were represented here, and some of the animals were already very sophisticated; trilobites for instance have eyes and a brain. According to Darwin's theory, the rocks below them should carry the simpler ancestors. They didn't, they appeared lifeless. It was as if most of the representatives of the animal kingdom were born in a single Cambrian explosion.

You begin to see Darwin's dilemma. Darwin sensibly surmised two things. First, the simpler ancestors might have been too squishy to fossilise. Second, given so much of the planet was yet to be explored, they might one day yet be found.

Darwin was at least half right. In 1947, the legendary geologist Reg Sprigg, found a fossil of the right age in the Flinders Ranges, in the Precambrian rocks of the Ediacara Hills. It was the beautiful leaf-like Dickinsonia: a plump oval shape with a midline ridge and veins splaying out to the sides. We now know that Dickinsonia was not a plant. It lived below the light zone and it also left tracks as it grazed peacefully on lawns of bacteria. And last year Ilya Bobrovskiy at Australian National University showed it produced cholesterol-like compounds, just as animals do.

I was privileged to attend the historic handover of Nilpena station last March. After three years of negotiation, it was a big day for Ross and his dynamo of a wife, Jane Fargher, who runs the Parachilna pub, a few kilometres from Nilpena station. Here she regales visitors with gourmet crocodile and kangaroo dishes, Ediacara-branded wines, home brewed beer, and fossil-inspired jewellery. But on March 28th, while Jane was laying on the final touches, Ross was off to the nearby airstrip to collect South Australian Premier Stephen Marshall, and his entourage.

The deal was signed in the 200-year-old limestone shearing shed. It was here, 30 years before, that a visiting relative and trainee geologist asked Ross about the rippled rocks on the floor of the wool shed. Ross took her to the gently sloping hills of nearby Mt Michael, where he'd seen plenty of rippled rocks during mustering. They turned over the rocks and found fossils.

For the past 17 years, Jim Gehling from the South Australian Museum and his colleague Mary Droser from the University of California at Riverside, have been studying the fossils. They invented the new field of 'paleoecology', not just describing the quirks of a new fossil, but studying the ecosystem within which it lived.

It turns out there is nowhere else in the world where this can be done. Although there is a Canadian site that also preserves an Ediacaran ecosystem, it is 5- to 20 million years older, and these Newfoundland creatures are quite unlike those at Nilpena. They consist of a very simple approach to making a body, repeating fractal forms, like you'd see in a branching plant. None of their kind went on to populate the Cambrian.

Nilpena is a freeze-frame of what happened next, when creatures with bilateral symmetry appear and leave tracks and burrows. Are they the answer to Darwin's dilemma? Did they indeed give rise to the Cambrian explosion? Thanks to the protection of Nilpena cattle station, the palaeontologists will continue to nut out the mystery for generations to come.

Robyn Williams: Ella Finkel, who still writes for Cosmos magazine and has a terrific piece in the latest edition. Thanks Ella for the good news.