Sunday, March 16, 2014

oldest zircon

I want to tell you the story of three rocks, starting with the oldest one ever found. That one is so small, if you put it in the palm of your hand you'd need a magnifying glass to spot it. It was found buried inside a hunk of sandstone near a sheep ranch in a remote part of Western Australia called the Jack Hills. It's not really a rock. It's a crystal, a zircon crystal, formed when the world was very, very young — about 4.374 billion years ago, as my NPR colleague Nell Greenfieldboyce recently reported. We know its age because we can measure how much uranium in it had decayed to become lead, and measure the movement of individual atoms (see Nell's story for details). Scientists are convinced that this crystal is so ancient it froze into place not too long after the moon was formed. It's that old.

If Only ...
Excuse me here, but I can't help myself — if that crystal had eyes, it would have looked up and the moon would have been 10 times bigger in the night sky. The moon was closer then. Oh, the amazing things an object that old might have seen as 4 billion years rolled by.

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