Uluru is the most iconic natural landform in Australia — and its formation is an equally special story of creation, destruction and reinvention.

The origins of Uluru (and Kata Tjuta) date back about 500 million years, to around the same time the Australian continent was formed.

Large crustal blocks were merging together to create the island of Australia — a process similar to the way India is ramming into the Eurasian continent today. As a result, Himalayan-sized mountain ranges were being built.

The rocky material that ultimately became Uluru and Kata Tjuta was in one of the mountain ranges formed — the Petermann Ranges.

Map Map of Kata Tjuta and Uluru

Creation and destruction of a mountain range

Planet Earth was a different world back then; there were no land-based plants and it would be another 250 million years before dinosaurs roamed.

"The whole landscape was very different that far back, there were no land plants plus we think the climate at that time, after a series of ice ages, may have been desert climate," said geologist Dr Marita Bradshaw, formerly with Geosciences Australia.

The newly-formed Petermann Ranges were similar in size to the French Alps or the Himalayas. But without any plant cover they eroded rapidly.

"We had these high mountains with granite outcropping and shedding of conglomerates which ended up being the rock type that we see at Kata Tjuta," said Dr Bradshaw.

The sediments that make up Kata Tjuta were moved by a river system into an alluvial fan.

However, the sand that became the arkose sandstone of Uluru was dumped at the bottom of the mountain range.

"What we see in Uluru is almost just shedding of granite," said Dr Bradshaw.

"It's got the big feldspar crystals in it which means it was very close to the source and it hadn't been in a big river system being shifted for a long time, so not much chemical or mechanical erosion happened to it."

Reinvention into the rock we see today

After this long period of rapid mountain building and erosion the centre of Australia turned into an inland sea and a phase of deposition began in what is now known as the Amadeus Basin.

"There was limestone and sand and mud deposited in the Amadeus Basin and that buried the arkose and conglomerate that eventually formed Uluru and Kata Tjuta," said Dr Bradshaw.

Around 400 million years ago the sands and gravels of Uluru and Kata Tjuta were so far down, and under so much pressure, they changed from sediment into rock.

Another mountain-building event, known as the Alice Springs Orogeny, began around this time. Over millions of years, this event created the great big folds visible when you fly over Central Australia today. The rocks making up Uluru and Kata Tjuta were also involved.

"What that does is really push down and fold the rocks that become Uluru and Kata Tjuta," she said.

After a long phase of erosion that lasted hundreds of million of years, Uluru and Kata Tjuta eventually emerged from the softer rocks.

"And it stands together as a really coherent and welded-together rock that has been etched and polished over tens of millions of years to be the beautiful Uluru that we see now."

Uluru is special

The 'spines' of Uluru in this image are the original layers of sediment eroded from the Petermann Ranges, tilted on their side. ( GettyImages/Geoffrey Clifford )

"The original sediments that formed Uluru and Kata Tjuta were special in their own way," said Dr Bradshaw, "because they were coming right off a big mountain range."

"And then the deformation of it was also special. It's really welded together as a rock."

The deformation flipped the sediments on their side so the originally horizontal layers of sand and gravel, known as the 'bedding planes', are now vertical.

And the rock is incredibly hard.

"You would expect Uluru to start breaking up along the bedding planes, which are now vertical, but it doesn't, so it's really been welded together well."

The rock that sticks up now as Uluru was probably in a tight fold, said Dr Bradshaw, and that may be why the rock itself is so hard, resistant and homogenous.

"The apex of the fold is where the pressure is highest and that's where the fluids that solidify and stick it together are concentrated."

Why is the rock red?

The red colour of Uluru is due to the oxidation or the rusting of the iron-bearing minerals within the rock as it has sat there in the desert air for hundreds of thousands of years, said Dr Bradshaw.

"The fresh rock which has not been in contact with the atmosphere is grey in colour."

As to the original Petermann Ranges, you can still see the 'nubs' or 'roots' of this once mighty range today, Dr Bradshaw said.