The origin of Ayers Rock1
To the tourist industry, it’s a real money spinner. To its European discoverers in the 1870s, it was a rock that appeared more wonderful every time it was viewed. To the Australian Aborigines, it was a place of shelter and special ceremonies. In some of their legends it came into being as a result of 40 days and 40 nights of rain. To the geologists, however, it has been a perplexing puzzle, so they have largely ignored it.
But despite the silence of the geologists, the publicity from the tourist industry has ensured that Ayers Rock has become one of Australia’s most famous landmarks. Situated in Australia’s arid red heart, the Rock is almost 460 km (285 miles) due south-west of the township of Alice Springs. Visited by thousands of tourists each year, it rises abruptly on all sides from the surrounding flat desert plains to a height of about 350 m (1,140 ft). This single massive Rock measures 9 km (5.6 miles) around its base, and stands in an awesome and solitary grandeur that can be only fully appreciated by those who visit its silent and desolate abode in Central Australia.
Even though geographers such as the noted Australian Dr C.R. Twidale2 have intensely studied the multitudinous erosion features on the face and at the base of the Rock, and believe they understand the erosion process that has shaped and produced Ayers Rock, geologists have said little about the origin of the material that makes up Ayers Rock.
Some geologists have proposed that the Rock evolved slowly some 550 to 600 million radiometric years ago, when sandy material was slowly scoured from the Musgrave Ranges and moved 100 km (63 miles) northwards by water slowly moving into a large depression (Figure 1). This accumulation process, they claim, would have taken many millions of years to build up the massive thickness of rock layer that comprises Ayers Rock. Then about 350 million radiometric years ago, the sandy material, by that time hardened to form sandstone, is thought to have been pushed up and tilted by earth movements. Over the next 250 million years slow erosion processes carved out the present shape of Ayers Rock, a shape which they say has been little changed over the past 100 million years.
But this evolutionary story about how Ayers Rock came to be illustrates why geologists have not said a great deal about the origin of the material in it, since the material within Ayers Rock actually contradicts the story of slow formation. So just what is Ayers Rock made of and how did it get there?
What is Ayers Rock?
Now while most tourists may think that Ayers Rock is simply a big boulder resting on the desert sand, it is anything but that! Ayers Rock is really just the ‘tip of the iceberg’. Geological exploration has revealed that there is even more of the same rock under the ground, and beneath the surrounding desert sands. In fact, it turns out that all this sandy rock material makes up one single bed or rock layer tilted so that it now stands almost up on its end. When measured, this single bed is at least 2.5 km (1.6 miles) thick, but that is only the thickness of the material which makes up the exposed part of Ayers Rock. The hidden part of Ayers Rock under the surrounding desert sands shows that the entire bed is in the order of some 6 km (3.75 miles) thick.
The actual material that makes up Ayers Rock is a particular type of coarse sandstone. Technically, it is known as arkose because it contains the mineral feldspar. It is this pinky-coloured mineral, along with the rusty coatings on the sand grains, that gives Ayers Rock its overall reddish colour. When you examine a piece of this Ayers Rock sandstone closely, you find that the mineral grains in it have a fresh and shiny appearance, especially the feldspars. The grains are often jagged around the edges, not smooth or rounded. The rock consists of large and small grains all mixed up in the same layer, a situation which geologists usually describe as ‘unsorted’.
Now this is not the kind of evidence you would expect to find if Ayers Rock had been formed slowly over millions of years, and had then endured further long periods of exposure to weathering at the earth’s surface. Feldspar minerals break down relatively rapidly when exposed to the sun’s heat, water and air (for example in a hot, humid tropical climate), and very quickly form clays. If the Ayers Rock sandstone had been exposed to the destructive forces of erosion and tropical weathering for 350 million years as evolutionists claim, then the feldspar minerals would have long since turned to clay. With the feldspars turned to clay the sandstone would have become weakened, and then collapsed as the clay and remaining mineral grains were entirely washed away, leaving no Ayers Rock at all. Furthermore, sand particles which are moved back and forth by moving water over vast eons of time, lose their jagged edges and become rounded and smooth. At the same time, these same particles being acted upon by the moving water over a long period of time would also be sorted, so that the larger particles and the smaller particles would be separated by the action of the water. This sorting action can be seen today in a river bed, where the small grains are carried along when the current is slow, leaving behind, and separating them from, the large rocks that can only be moved when the current is swifter. Thus, if the sandy material at Ayers Rock had taken millions of years to accumulate as evolutionists claim, then the resultant sandstone should have had smooth rounded grains that had also been sorted into separate layers of either small or large particles.
So fresh shiny feldspars, jagged grains and unsorted particles all indicate that the sand accumulated so rapidly the materials did not have enough time to be weathered by the sun’s heat, water and air or to be sorted, since they were rapidly transported from their source of origin and then simply dumped and buried in a heap.
How was it formed?
There can be no doubt the sand was certainly washed into a vast depression, and that it had been scoured from the Musgrave Ranges, but the whole process must have been catastrophically rapid. One only has to consider the amount and force of water needed to dump some 6,000 m (approx. 20,000 ft) of sand, probably in only a matter of hours, after already having carried this sand some 100 km (63 miles), to realise that such an event had to be a catastrophic flood. This traumatic flood also had to be a recent event, otherwise the feldspar mineral grains in the sandstone would not appear as fresh and as unweathered as they are today if they had endured at least 350 million years of exposure to the sun’s heat, water and air in the tropical climate that Twidale suggested.2
Since the beds are now standing vertically, it is also obvious that the sand after being washed into the depression, and while still being compressed and hardened, was pushed up and tilted by earth movements. How was it then shaped into its present form? Twidale, the noted Australian geographer and world leader in the study of landforms and landscape-forming processes, is emphatic that the evidence at Ayers Rock points unequivocally to rapid water erosion of the Ayers Rock sandstone in a hot, humid tropical climate, not a desert climate like that in Central Australia today. Twidale’s observations and conclusions are certainly consistent with the idea that the modern landform of Ayers Rock developed as the same catastrophic floodwaters which dumped it in its vast depression began to retreat away from the uplifted land surface, scouring and eroding the soft and still fairly loose sand to leave behind the landform we now know as Ayers Rock.3 This process continued as the waters of that flood continued to retreat off the rising Australian continent. Indeed, many scientists from diverse specialities agree that Australia is a continent that is still drying out after being very wet in the recent past. Following the retreat of these floodwaters, and as the landscape dried out, the material in Ayers Rock hardened. The chemicals in the water between the sand grains formed a cementing material to bind the mineral grains together, drying in much the same way as cement in concrete dries and binds together the stones and sand mixed with it. With the final retreat of the waters from off the land, and the continued drying out of the continent, present day desert wind erosion has merely pock-marked the surface of the Rock.
It is hardly surprising then that most geologists today are puzzled by Ayers Rock, because the evidence there does not fit into their evolutionary story with its vast eons of slow erosion and deposition, then slow erosion again. Instead the evidence at Ayers Rock is much more consistent with the scientific model based on a recent and rapid, massive, catastrophic flood, such as that of Noah’s day.
References and notes
- This article was originally published in 1984 before Ayers Rock became known as Uluru. Return to text.
- Twidale, C.R., and Wopfner, H., Aeolian landforms of Central Australia: a discussion, Zeitschrift für Geomorphologie Neue Folge 25(3):353–358, 1981. Return to text.
- From 1985, it became known as Uluru. Return to text.