The Browning of Australia & The First Revolution

First published: National Geographic June 2010

Written as part of the TV series 'How Earth Made Us'. This series is also known as 'How The Earth Changed History' on National Geographic, USA.

Paul Williams, Assistant Producer

The First Revolution

Between 10 and 7 thousand years ago a revolution swept across the world which would lay the foundations for the development of human civilization. It was the Neolithic revolution - the age of farming. While China ploughed rice and millet in the fertile soils of the Loess Plateau, Mesopotamia grew along the banks of the Tigris and Euphrates. In Australia, on the other other side of the planet, a very different story was playing out.

Australia did have one thing in common with these 'cradles of civilisation' - well crafted stones tools. Used for grinding seeds they can be found scattered across the continent, some dating back 30,000 years - 20,000 years earlier than anywhere else on Earth. In most civilizations these tools seem to be a prerequisite for the Neolithic transition but here, given a head-start, farming never took off.

You might think that’s because it’s parched and dry. But it’s just as much to do with the wind.

The Eternal Joy Ride

The Australian continent sits right atop the Indo-Australian tectonic Plate, on an eternal joy ride around the planet. It is placed neatly at the plates centre, far away from the edges where a destructive regime of earthquakes and volcanoes operate. Because of this positioning Australia remains tectonically stable, solid as a rock. Geologically it is rather a boring continent - and it has been for more than 400 million years.

65 million years ago, while dinosaurs where breathing their last, Australia was commencing a slow northward journey leaving behind the cool chill of the polar region and eeking its way towards warmer climes snugly situated between 10 and 43o latitude. This led Australia straight into the hands of one of the planets most powerful phenomena - The Hadley Cell, a giant powerful circulation of air which wraps around the entire globe.

These cells have a grasp on the planet which begins at the equator. Here the sun is at its hottest – so the air is continually rising, as it rises over the tropics any moisture condenses and falls on the rainforests below - an equatorial band of thunderstorms mark out its ascension. At a height of 10 to 15kms the dry air cools as it continues to spread away from the equator, until between 20 and 30 degrees latitude it sinks back to Earth, heating up again in the process.

Image: The Hadley Cell, At the surface the descending air flows back towards the equator. These are the trade winds. They close the loop and form what's known as an atmospheric cell. It's the spin of the earth that deflects these surface winds so they move towards the Americas. Each hemisphere has 3 giant atmospheric cells which define the prevailing surface winds around the entire Earth. East-West Movements of the atmospheric Cells.

The Browning of Australia

This pattern of winds creates a band of hot, dry deserts around the world on either side of the equator, including the Sahara and Arabian deserts in the northern hemisphere. In the Southern Hemisphere it meets Australia. During its interminable progression northwards the climate of Australia became ever more variable as it slowly coincided with this atmospheric hotspot. The red continent essentially found itself sitting beneath a huge atmospheric hairdryer which for the past two and a half million years has blasted dry hot air onto it, creating half a million square miles of desert and leaving a continent parched and dry - what Mary E White described as the Browning of Australia.

To really appreciate this browning it helps to be in the centre of Australia, and to be up high. Mount Connor, Attila to the aborigine people, is a monolithic giant standing proud in an otherwise flat and featureless landscape. It lies at the geographical and spiritual centre of Australia, and it also lies at the heart of an incredible circular wind system. The descending air is influenced by a myriad of atmospheric protuberances, and deflected by the spin of the earth, to create a giant anticlockwise swirl around most of the continent.
 

 Image: Mount Connor 'Atilla', central Australia

A Continent Laid Bare

These swirling winds have a profound effect at ground level. Australians are familiar with a landscape they call Gibber - the 12,000 square miles of the Stoney Desert is almost nothing but Gibber. More commonly known as desert pavement, it forms when winds strip away fine material leaving behind larger rocks which interlock to look like crazy paving. This acts like an armoured cap to the landscape preventing vegetation from taking root. With minimal vegetation to anchor sediment in place fertile dust and nutrients continue to be blown away. On other continents this fertility may be continuously replenished by material washed down river from mountains - the Euphrates in the middle east, the Ganges in India, the Yellow River in China, but on a tectonically stable and flat continent such as Australia the mountains have long since dissapeared and there is very little left from which to replenish the fertility. While the winds brought fertile dust to China, in Australia it simply whips it away, so much so that across vast expanses of the continent all that remains is sand and stone. Where Gibber isn't formed the sand has been shaped into vast fields of long parallel dunes which circle Australia – all lined up with the path of the winds...

 Australian Gibber 'Desert Pavement'

It’s a process that continues to this day. Giant dust storms regularly engulf Eastern Australia. In 2009 a dust plume more than 500 kilometres (310 mi) in width and 1,000 kilometres (620 mi) in length swept over New South Wales and Queensland loaded with more than 16 million tonnes of dust blown from the deserts of Central Australia. At its peak the Australian continent was estimated to be losing 75,000 tonnes of dust per hour, most of it is deposited at sea where its nutrients provide an essential part of the marine food chain.

Over millions of years the winds and the planets tectonic forces conspired to deal a tough hand to the ancient peoples of Australia. With large areas of the continent bare and arid, continuing with a hunter gatherer lifestyle made more sense than taking up farming. Rather than relying on one or two intensive crops, they diversified into a wide range of wild food sources. And instead of living in permanent settled communities they lived in small, mobile groups, always able to move in search of food.

A dust storm obscures the Sydney Opera House at sunrise Sept 2009. REUTERS/Tim Winborne