Tiny Crystal Believed to Be Oldest Known Solid on Earth

Scientists have found a crystal believed to be at least 4.3 billion years old, making it the oldest known solid on Earth. The grain of zircon, hardly wider than a human hair, was born in a molten fury not long after Earth formed. It was discovered inside younger stone in what is now Australia, two international research teams report in today’s Nature.

Zircon is made of silicon, oxygen and zirconium, among other elements. The oldest crystal identified is one of a dozen extracted from the Jack Hills section of northwestern Australia. Researchers said the zircon’s high level of heavy oxygen isotopes suggest it was cooled by surface water after it formed, meaning that oceans appeared 200 million to 300 million years after Earth’s formation, 4.56 billion years ago.

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--Compiled by Times medical writer Thomas H. Maugh II