FINDING a piece of original crust requires an epic journey to the frigid north, the scorching outback, or maybe even beyond the bounds of Earth itself.
The first stop on our odyssey is Yellowknife, capital of Canada鈥檚 Northwest Territories. A journey 350 kilometres north of the city brings you to the Acasta Gneiss, a 4.03-billion-year-old outcrop that contains the oldest known rocks still firmly attached to our planet.
But we have long known that Earth is 4.56 billion years old, and that the crust solidified shortly afterwards. Are there any chunks of crust older than the Acasta Gneiss, or has plate tectonics obliterated all traces?
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The answer lies in the Jack Hills of Western Australia. Amid rock formations 3.8 billion years old, researchers have recently found small, tough minerals called zircons that have survived for some 4.4 billion years. These are the oldest known minerals anywhere on the planet.
That doesn鈥檛 mean there aren鈥檛 older ones around, however. 鈥淭he amount of Earth鈥檚 surface we鈥檝e examined closely is vanishingly small,鈥� says Mark Harrison of the University of California, Los Angeles. 鈥淚 think there are surprises still to come.鈥�
For those not willing to brave a journey to the ends of the Earth there may be an easier way to find super-ancient minerals 鈥� visit your nearest beach.
Because zircon resists weathering so well, small bits find their way onto beaches all over the world. On average, beach sand is between 0.03 and 0.04 per cent zircon. The vast majority of these grains will be younger than those from the Jack Hills so it鈥檚 unlikely that you will discover the world鈥檚 oldest mineral. But you never know. 鈥淭he chance is incredibly low,鈥� says Harrison, 鈥渂ut you can鈥檛 win the lotto if you don鈥檛 buy a ticket.鈥�
A more likely way to hit the jackpot is to take an even more epic journey 鈥� to the moon. Researchers believe the young Earth was regularly bombarded by asteroids and other impactors. Even small objects 100 metres in diameter could generate enough energy to fling pieces of crust out into space.
鈥淭here鈥檚 virtually no question that somewhere there is a fist-sized rock older than anything we鈥檝e seen,鈥� says Harrison. 鈥淎nd it鈥檚 probably resting quietly on the lunar surface.鈥� The only snag is getting there.
