Scientists have confirmed that a tiny zircon crystal is the oldest piece of the Earth's crust, at 4.4 billion years old.
The crystal was discovered on a sheep ranch in Perth, Australia in 2001, but researchers published a confirmation of the gem's age in Nature Geoscience this weekend. According to lead author John Valley, "this is the oldest and the best dated of all the crystals that have been reported." He adds that the crystal, which spans roughly 400 micrometers -- the width of a human hair -- across, is a clear red but shines blue when lit by electrons.
The scientists used a rigorous technique called atom-probe tomography to isolate and identify individual atoms of lead in the crystal, in order to make sure that they hadn't shifted in a way that would compromise their dating mechanism.
Valley explains that by analyzing the ratio of oxygen isotopes in the crystal, his team was able to determine that the Earth cooled much faster than scientists had previously thought -- meaning that it could have supported liquid water, and life, earlier than expected. CNN reminds us that the oldest fossils we have found date back 3.5 billion years, while the Earth itself is aged at 4.54 billion years. Rocks showing evidence of liquid water date back 3.8 billion years. According to CNN:
Very little is known about the first 600 million years or so of the planet's history, known as the "Hadean Eon" because it was thought to be "hell-like," Valley said. The leading theory is that Earth was bombarded by meteors in its early history. It took a big hit from an object the size of Mars about 4.5 billion years ago, leading to the formation of the moon. These impacts vaporized the Earth's crust and formed a super-hot magma ocean. Evidence including this zircon suggests that within the first 100 million to 200 million years of its existence, our planet cooled enough to make crust.