A remote rocky Australian landscape of kangaroos and giant lizards is also home to tiny ancient gemstones that have helped unravel mysteries about the early years of planet Earth itself.
The Jack Hills, named after a 19th-century pioneer and bushman, John 'Jack' Foley, is a range of rolling uplands covered in dry, rusty soil and blanketed with spiny grass and weather-beaten trees. Lying about 800km north of the city of Perth in Western Australia, the region is little visited and largely ignored except by a handful of iron-mining operations. You are more likely to see emus wandering this hot landscape than other human beings.
However, in the 1980s Australian geologists began discovering that the Jack Hills held an astonishing quantity of very old diamond-like zircons. These were found deposited in some of the rocky outcrops, particularly at Erawondoo Hill. In 2001, a joint team from Australian, the US and the UK unearthed what they believed to be the oldest zircon grains yet.
Scientists subsequently used atom-probe tomography and ion mass spectrometry to examine the mass of lead atoms in the sample and this helped them establish the age and thermal history of the zircons. They discovered that the stones crystalised some 4.4 billion years ago – in the Hadeon Eon – just 160 million years after the planet formed.
This makes the Jack Hills' zircons the oldest known rocks on earth and provides direct evidence of the Earth's first crust. But, even more extraordinarily, the ancient rocks also contained oxygen isotopes, which is evidence for surface water. The findings suggest that Earth was cooler and potentially more hospitable for life much earlier than previously thought.
The zircons at the Jack Hills are small and found in a host sandstone rock that is only 3 billion years old. It is thought that the durable zircons eroded from older rock and accumulated in riverbeds and depressions and, over time, became a component of the sedimentary sandstone that can be seen today in Jack Hills. If you want to see the world's oldest intact rock formations, then you have to visit Canada's Northwest Territories where Acasta Gneiss dates to 4.2 billion years ago.
If the early Earth suggested by the Jack Hills' zircons sounds inhospitable, the modern location is marginally more welcoming and is home to some impressive though hard to find wildlife. The iron-rich soil give a red-rusty look to the landscape, which is dominated by leggy mulga trees (of the genus Acacia) and rough, spiky grass. It is arid and hot so desert-adapted species are most at home here including red and western grey kangaroos as well as emus.
Reptiles are common including the perentie, which at 2.5m long is the fourth largest lizard species in the world. It is a powerful predator, outrunning other reptiles, birds and rabbits before dispatching them with a mildly venomous bite. It belongs to the monitor lizard genus Varanus, which includes the Komodo dragon. Monitor lizards are so-called for their ability to stand upright on its back legs and tail to get a better view and the perentie can run on four legs or even two. Extremely shy, the perentie is rarely seen but, if cornered, it will stand its ground and defend itself with claws, teeth and a whip-like tail.
While a giant reptile such as the perentie might hint at the Jack Hills' prehistoric past, the story here is far older and more profound, shedding light from billions of years ago on the origins of our own existence.
