Geology

Australia is Where You'll Find The Oldest Rocks On Earth

Where's the oldest place on Earth? Because plate tectonics constantly recycles our planet's crust, that's a difficult question to answer. Even so, scientists think they've done it: crystals discovered in the Jack Hills of western Australia appear to put them on the oldest continental crust on Earth.

Ancient Hills

In 2014, researchers published a study in the journal Nature Geoscience showing that parts of Australia's Jack Hills were a jaw-dropping 4.4 billion years old. To come to this discovery, the team shaved away tiny zircon crystals—we're talking no larger than a dust mite—from rocks they found in the Jack Hills. They contained radioactive atoms of lead dating back from when the crystals solidified from lava. The atoms started out as radioactive uranium, but over billions of years they shed nuclear particles to become lead. By dating the lead atoms directly, the researchers found that the crystals were probably around 4.4 billion years old.

Zircon crystals

How Old Is That?

Think of it this way: our planet is a little over 4.5 billion years old. The moon is about the same age. That means that the crystals found in the Jack Hills could have definitely formed in the lava ocean that covered our planet after the giant collision that created the moon. Ever feel old? You've got nothing on those hills.

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Key Facts In This Video

  1. Earth's outermost layer is constantly renewing itself, making the planet appear "younger." 00:21

  2. The mineral zircon is durable, like quartz, but contains small traces of radioactive uranium. 01:31

  3. Uranium-lead dating of zircon tells us that the Earth is at least 4.4 billion years old. 02:33

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Written by Curiosity Staff January 8, 2016