Environment

Hell Froze Over Earlier Than We Thought

Ancient diamonds suggest a thick skin on the early Earth.

By Clara MoskowitzDec 20, 2007 12:00 AM

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Geologists don’t agree on whether the infant Earth’s surface was hot and molten or stable and cool—or even when the first solid crust formed. What they do agree on generally is that the crust grew as material from Earth’s mantle, the middle layer of our planet, melted and rose to the surface, where it hardened. Now the discovery of tiny diamonds in a Western Australian site provides a new timeline for when this process began. Researchers led by Martina Menneken of Westfälische Wilhelms-Universität in Germany found that the diamonds are surrounded by zircon crystals, which were dated between 3.1 billion and 4.3 billion years old. Because many diamonds are formed in the mantle by intense pressure from the heavy crust above, the researchers suspect that some thick crust may have formed extremely early in the planet’s 4.5-billion-year history.

Another recent study looked into just how that crust formed. Geochemists Graham Pearson and Stephen Parman of Durham University in England examined bits of metal from the mantle that had been thrust up onto Earth’s surface by plate tectonics for signs that would indicate when the metal had been molten. The duo found that Earth’s interior had melted in large quantities at a few points in time. Parman says these measurements correlate to the ages of previously dated parts of the crust, thus supporting one popular theory that the continental crust came into being in a few distinct bursts.

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