You’re looking at the oldest fragment of Earth ever found: a zircon 4.375 billion years old, something that has deep implications in our understanding of the planet’s formation. While some scientists said other samples weren’t genuine, new research just published in the journal Nature Geoscience proves that this is the real McCoy.
John Valley — a geochemist at the University of Wisconsin, Madison — and his colleagues, used a new technique called atom-probe tomography. This technology allowed the scientists to count individual lead atoms within the zircons found in Jack Hills, a range in the midwest of Western Australia.
The previous method — which counted the number of lead isotopes — was imperfect because the radioactive uranium trapped inside the zircons moves lead isotopes around as it decays. According to Valley, “if there’s a process by where lead can move from one part of the crystal to another place, then the place where lead is concentrated will have an older apparent age and the place from where it moves will have a younger apparent age.”
Valley claims that atom-probe tomography doesn’t suffer from this defect, something that has allowed them to obtain the definitive age: “We’ve proved that the chemical record inside these zircons is trustworthy.”
Their research demonstrates that these zircons were formed only 100 million years after the massive cosmic impact that smashed Earth to create the Moon as we know it today. Since they think the crystals formed from granodiorite or tonalite — materials that are rich in water — this means that Earth cooled down really quickly. So fast, in fact, that it’s possible there was water on its surface, says Valley:
The zircons show us the earliest Earth was more like the Earth we know today. It wasn’t an inhospitable place.