We are taking a look back at stories from Cosmos Magazine in print. In March 2024, geology professor Alan Collins took us hiking to his favourite place to see the world – present and past – through his eyes.
I’ve always liked mountains. When I was young, I didn’t understand much but I felt a visceral connection with the rocks, always seeking out crags to scramble on, drawn to scars and pocketing rocks, more intrigued by their textures than having any deep insights into their origin. Decades later, I’m a geology professor at the University of Adelaide and I’ve learnt to read the rocks to glimpse our planet’s deep history. There is delight in this, but also vertigo as I peek into the temporal abyss and see all that I don’t know: hints of cataclysms and past worlds.
For a decade I’ve taken students on field trips to teach them to read the rocks too, and I’ve had the privilege of witnessing the discombobulating, revelatory moment when it first clicks – and they begin to see the deep-time history of a place.
My favourite place where this happens is Nhawiranha (Devil’s Peak) in the southern Flinders Ranges, 300 kilometres north of Adelaide on Nukunu Country. Let me take you there, too, and show you the story of the landscape.
Climb with me up the short, steep path on the peak’s east flank, at first through the sparse forest, needing to use our hands a little to get over the pale sandstone ribs, then up the exposed trail. On the ridge, we’re surrounded by stunted old sugar gums. Scramble the last rocky bit to the summit and now we’ve arrived in the most spectacular lecture theatre I know.
We are sitting on a natural sloping rock shelf 700 metres above the Spencer Gulf, which we can see to the south-east. To the north the ranges sharpen to the mountains of Ikara/Flinders Ranges National Park. Look west and follow the dip of the rocks and you’ll see the panorama revealed over Pichi Richi Pass – a place of passage, marked today by road and rail that follow the traditional trading route of the stimulant pituri from central Australia to the coast.
The ridges, valleys and creeks of Pichi Richi are visually striking – but look closer: we can see time. The huge fold that now forms the framework of the pass shows us where the ground buckled half a billion years ago, when the ancestor of the Pacific Ocean plate scraped its way beneath this ancient edge of Australia.
The rocks in our view preserve subtle features of the landscape we would have seen if we had stood here 630 million years ago.
The rocks in our view preserve subtle features of the landscape we would have seen if we had stood here 630 million years ago. The oldest rocks, in the core of the pass, have memories of ice sheets, of glaciers scouring the region, of meltwater-ravaged plains in front of melting ice. A minuscule magnetic field preserved by magnetised minerals in these rocks shows that frozen seas covered the equator. Back then Earth would have looked like a giant snowball, more like desolate Pluto than our beautiful blue planet. Today, these rocks form the scrubby low hills of the summit of the pass, laid out before us as we look down from the vantage of Nhawiranha’s summit.
Later, on your way home, stop by the side of the road in the pass and touch the dark, millimetre-thick bands that cross between metre-thick layers on the valley floor. These mark the rippled dunes that advanced over the beds of a shallow sea that formed after the ice sheets melted. These rocks belong to the Ediacaran Period, a duration of geological time, from 635–539 million years ago. It is the only geological period named from a Southern Hemisphere feature: the Ediacaran Hills, 100 km north-west of where we are now. If you look up from the valley floor, back towards the west slopes of Nhawiranha, you can trace how the fine-grained Ediacaran purple mudstones turn into white, hard, ridge-forming sandstones further up the slope: millions of years of sediment deposits, filling in the ancient Ediacaran seaway.
Back on the summit, you can spot where the rocks of the pass have been cut away to build railway tracks. One of these cuttings at the south end of our view is lined with the same hard, white sandstones. But here they have a characteristic beehive-like pattern, from ancient mud cracking as this now-shallow lagoon dried up 600 million years ago.
So far, the story we’re seeing in the landscape is from a time before animals. But come back to the sun-warmed rocks we’re sitting on here on the summit. These are the youngest rocks of the area, and just below us, the rocks we puffed our way over earlier contain some of the oldest fossil animals on the planet. They’re 550 million years old: a waymarker on our planet’s path to habitability.
This is what I see when I look at the landscape from the summit of Nhawiranha – not just the world of today but the many worlds of the last billion years. I hope you can see it too: all these times held together by Nukunu Country, the place where wedge-tailed eagles fly.