Water in the desert.
Imagine what that meant to the early inhabitants of inland Australia in one of the harshest
and most arid places on the planet for them to know that they had permanent access to
fresh water and wetlands.
No wonder Australia's natural spring systems became so sacred for so many.
But when the lakes turn to salt pans and the rivers are sucked dry where does the water
come from?
Okay, get your head around this.
About two million years ago it rained on the Great Dividing Range in Queensland.
Today that same water bubbles up in South Australia.
Think about it.
The last time this water saw the light of day giant hippopotamus-sized diprotodonts
were grazing on the coast, the Tasmanian Tiger was alive and hunting and Australia was the
home of a lion called the Thylacoleo that had the strongest bite of any mammal in history,
living or extinct.
So, this water has been travelling at a painfully slow pace through porous rocks deep underground.
Sometimes it bubbles and soaks its way to the surface through natural springs.
At other times we've found ways to dig down and find it.
Either way, it is the key to life to about a quarter of the continent.
We call it the Great Artesian Basin.
To explain how the Great Artesian Basin works you need to know how it came to exist in the
first place.
So here it is, the past 250 million years in a nutshell.
Back in the Triassic Age Australia was joined together with the other southern continents
including Antarctica, South America, Africa and New Zealand in a land mass called Gondwana.
Now have a look at the top right quarter of Australia.
Can you see how it kind of forms a natural dip?
That's the area that will eventually become the Great Artesian Basin.
Over the next 140�million years huge events like ice ages in Europe and tectonic plate
movements cause the ocean level to rise and fall.
When the ocean levels rose water became trapped in that natural dip and formed a sea.
But when the ocean levels fell the whole area became land again.
When the seas drained away they left clay and silt deposits behind which hardened into
impermeable stone.
Remember this.
So now we're back to dry land again but it's not desert yet and there are rivers crossing
it.
The rivers carried sand and gravel with them which later joined together to form sandstone
and that sandstone is the key to how the basin works.
Silt stones and mud stones are what scientists call impermeable.
There's no way water can get through them.
They're like plugs.
Check this out.
Okay.
We've got our impermeable rock and we've got our sandstone.
Okay.
It ain't going through.
Soaking it up.
Now we wait.
Okay.
Imagine our layers of impermeable and permeable stone deep underground.
I'll demonstrate.
This sponge is our sandstone, our permeable layer and if you see the water, it goes straight
through it.
But if we put an impermeable layer - this frisbee � underneath, the water has nowhere
to go except forward or to the sides.
When that happens the layer of sandstone is called an aquifer.
It's a massive area.
It stretches from Cape York to Dubbo and Coober Pedy to the south-east corner of the Northern
Territory.
That's almost a quarter of Australia.
When it rains on what we call the recharge bed areas of the basin the water seeps down
and collects in the aquifers.
Scientists estimate that there's around 65,000 million megalitres of water in the basin right
now.
A megalitre is a million litres.
65,000 million of them would be enough to cover all the land on the planet in almost
half a metre of water.
So that whole basin area we saw earlier now has aquifers running all the way through it
and has become the Great Artesian Basin.