Quick answer: the oldest known material formed on Earth is a zircon crystal from the Jack Hills of Western Australia, about 4.4 billion years old, formed roughly 160 million years after the solar system itself. It measures only about 200 by 400 microns, roughly twice the width of a human hair. Its age was confirmed in 2014 by counting individual lead atoms inside it.
Why the oldest crystal is a zircon
Earth recycles its crust constantly. Most surface rocks are less than a few hundred million years old (History.com). Very little survives 4 billion years of plate tectonics, erosion, and melting. Zircon (zirconium silicate) is the exception: it’s hard, chemically stubborn, and survives being eroded out of one rock and buried in another. This grain, reported in 2001, came out of a much younger sandstone, grains that had outlived their parent rock by billions of years.
Zircon has a second superpower: when it crystallizes, it happily takes in uranium but almost completely rejects lead. So virtually all the lead inside a zircon was made by uranium decaying after the crystal formed. That makes zircon a built-in clock.
How do you prove a crystal is 4.4 billion years old?
The 2014 study, led by John Valley at the University of Wisconsin-Madison and published in Nature Geoscience, combined two methods: secondary ion mass spectrometry and atom-probe tomography, which maps individual atoms (UW-Madison). They found the lead atoms were not spread evenly but bunched in clusters smaller than 50 atoms across, “raisins in a pudding.” Those clusters formed about a billion years after the crystal did, which ruled out the worry that lead had moved around and faked an old age.
What a single grain told us about early Earth
The oxygen chemistry in these zircons points to a “cool early Earth” with liquid water. Valley: “The study reinforces our conclusion that Earth had a hydrosphere before 4.3 billion years ago” (UW-Madison). Oceans, in other words, appeared surprisingly soon after the planet formed, and life may have had a head start.
How old are the crystals in a rock shop, by comparison?
- Herkimer diamonds: grown in cavities of roughly 500-million-year-old Cambrian dolostone. Old, but about a ninth of the Jack Hills zircon’s age.
- Libyan Desert Glass: formed about 29 million years ago.
- Long Island petrified wood: a tree turned to stone, with the minerals arriving long after it died; see our post on how it got here.
- Naica gypsum: under a million years. See How long does it take a crystal to grow?
Older than Earth?
Yes, if you count things that fell here. Some meteorites contain grains older than the solar system (presolar grains), and the oldest solids in meteorites date to about 4.57 billion years. But the Jack Hills zircon is the oldest crystal known to have formed on Earth. See Meteorites: how to tell a space rock from a hot rock.
FAQ
Can I buy a Jack Hills zircon? Not realistically. The ancient grains are microscopic, have to be dated one by one, and the record holders are scientific specimens.
Is zircon the same as cubic zirconia? No. Zircon is a natural mineral; cubic zirconia is a lab-made zirconium oxide diamond simulant.
Related reading
- Mineral evolution: why Earth has 6,000 minerals
- Banded iron formations
- What is 1,000 times rarer than a diamond?
Related pieces in the shop
- Herkimer Diamond Quartz Cluster on Matrix, Mohawk Valley NY
- Libyan Desert Glass, 3 pieces
- Petrified Wood, Long Island NY
Sources: University of Wisconsin-Madison, “Oldest bit of crust firms up idea of a cool early Earth” (Valley et al., Nature Geoscience, 2014); History.com.
