Where Are The Oldest Rocks On Earth?
The oldest of the zircon crystals examined by scientists was 400 micrometers long, about the size of a dust mite. It contained radioactive atoms of lead that had started out as uranium and undergone decay. Analysis of the crystal suggested that the Jack Hills are indeed the oldest part of Earth's crust, having formed a mere 160 million years after the birth of the solar system, and very close to Earth's formation 4.5 billion years ago.
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Key Facts In This Video
Earth's outermost layer is constantly renewing itself, making the planet appear "younger." (0:21)
The mineral zircon is durable, like quartz, but contains small traces of radioactive uranium. (1:31)
Uranium-lead dating of zircon tells us that the Earth is at least 4.4 billion years old. (2:33)