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At 4.4 Billion Years Old, Oz Crystals Confirmed As World's Oldest

Feb 24, 2014
Originally published on February 24, 2014 1:06 pm

Scientists have used a powerful new technique to prove that some tiny crystals found in Western Australia are indeed the oldest known materials formed on Earth.

Back in 2001, scientists reported that one of the zircon crystals was about 4.4 billion years old — so old that not everyone believed it.

"There have been challenges, because nothing in science goes without being questioned. It always has to be proven," says John Valley, a geochemist at the University of Wisconsin, Madison.

The crystals formed just tens of millions of years after an early proto-Earth was melted by a violent impact with a Mars-size object. The crash created the moon and turned our young planet into a red ball of molten rock.

"It would have glowed almost like a star. Nothing could exist on the surface. There would be no continental land masses. There'd be no liquid water. And there certainly would have been no life at that time," says Valley.

The bits of zircon suggest that those fiery, inhospitable conditions actually didn't last long — that the Earth's continental crust formed early on, and the planet started being more homey.

The crystals are so tiny that if you had one in the palm of your hand, you could not see it without a magnifying glass. Some have jagged edges, while others look like smooth jellybeans. "The colors can be anything from transparent to a deep red," says Valley.

Geologists found them on a sheep ranch in a remote part of Western Australia called the Jack Hills, in sandstones that were a beach around 3 billion years ago.

"It's always blown my mind," says Valley. "I mean, to collect samples that were on a beach 3 billion years ago — and to find crystals that were more than a billion years older even than the beach — is just really surprising and wonderful."

In their original report, Valley and his colleagues had determined the antiquity of the crystal by looking at a small part of it and analyzing how much of the element uranium had decayed into lead.

But some scientists pointed out a potential problem: Atoms of lead might move around inside the crystal. "And if that happens, in the places where it's concentrated, you will measure an older age than the true age," Valley explains.

So Valley's team recently tackled this issue with a powerful new instrument that can pluck out and identify individual atoms, to create a kind of map of their distribution inside the crystal.

They found that lead atoms do move around, but only a tiny bit — not enough to affect their age calculations. This particular crystal that they analyzed, they say, is 4.374 billion years old, plus or minus 6 million years.

Sam Bowring, a geologist at the Massachusetts Institute of Technology, says it's pretty hard to argue with this new study, which appears this week in the journal Nature Geoscience.

"I think people will be impressed with the technique and impressed with the conclusions and agree with them," he says.

Having something that appeared so soon after the Earth-moon system was formed means that scientists are closing the gap in the part of the Earth's history that is not preserved, says Bowring.

"I think that really is profound, if you think about it," he says. "Now we're talking about a history on this planet that goes back to almost the day that the planet was born."

If geologists are lucky, he says, someday they may stumble over a big rock that's as old as these little crystals.

Copyright 2018 NPR. To see more, visit http://www.npr.org/.

DAVID GREENE, HOST:

Scientists can show restraint when it comes to superlatives. Think something is the biggest or fastest? Prove it, they say. But it turns out scientists love them because something extreme can help answer interesting questions. NPR's Nell Greenfieldboyce reports on bit of crystal that is so old, it can tell us about some of the Earth's earliest days.

NELL GREENFIELDBOYCE, BYLINE: Our planet's history stretches back more than four and a half billion years. First a spinning cloud of gas and dust coalesced to become our sun. Then clumps of matter started slamming together, forming planets. Scientists think that after a proto-Earth emerged, an object the size of Mars smashed into it. The crash created our moon and turned the Earth into a red ball of molten rock.

JOHN VALLEY: It would have glowed almost like a star. Nothing could exist on the surface. There would be no continental land masses. There'd be no liquid water. And there certainly would have been no life at that time.

GREENFIELDBOYCE: John Valley is a geochemist at the University of Wisconsin-Madison. He wonders: How long did those fiery conditions last? When did land appear, when did our planet become homey? Valley thinks it happened pretty quickly. And his evidence lies inside ancient sand grains that were once part of an early continent.

VALLEY: These are the oldest known materials from the Earth.

GREENFIELDBOYCE: Valley says the sand grains are actually tiny zircon crystals.

VALLEY: So if you have one zircon in the palm of your hand, you won't see it without a magnifying glass.

GREENFIELDBOYCE: Some crystals have jagged edges, others look like smooth jellybeans.

VALLEY: The colors can be anything from a transparent to a deep red.

GREENFIELDBOYCE: Geologists found them on a sheep ranch in a remote part of Australia in sandstones that, three billion years ago, were a beach.

VALLEY: It's always blown my mind, I mean to collect samples that were on a beach three billion years ago and to find crystals that were more than a billion years older even than the beach is just really surprising and wonderful.

GREENFIELDBOYCE: Back in 2001, Valley and some colleagues reported that one of these grains was around 4.4 billion years old, so old that not everyone believed it.

VALLEY: There have been challenges because nothing in science goes without being questioned; it always has to be proven.

GREENFIELDBOYCE: Valley and his colleagues had determined the crystal's age by analyzing how much of the element uranium had decayed into lead. They did this by looking at a small part of the crystal. But some scientists pointed out a problem - lead atoms might move around inside the crystal.

VALLEY: And if that happens, in the places where it's concentrated, you will measure an older age than the true age.

GREENFIELDBOYCE: So Valley's team recently tackled this issue with a powerful new instrument that can pluck out and identify individual atoms. They found that, yes, lead does move around but not enough to affect their age calculations. So they do have the oldest known material of any kind formed on Earth. Sam Bowring is a geologist at MIT. He says it's pretty hard to argue with this new study, which appears in the journal Nature Geoscience.

SAM BOWRING: I think people will be impressed with the technique and impressed with the conclusions and agree with them.

GREENFIELDBOYCE: He says it means continents must have formed just tens of millions of years after the big impact that created the moon.

BOWRING: I think that really is profound, if you think about it, and now we're talking about a history on this planet that goes back to almost the day that the planet was born.

GREENFIELDBOYCE: He says if geologists are lucky, someday they'll stumble over a big rock as old as these little crystals. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.