A crystal of zircon found in rural Australia was dated by scientists to be approximately 4.4 billion years old on Sunday, making it the oldest known piece of Earth’s crust in existence.
The crystal was found in a hot, arid region of Australia near Perth, one of Australia’s largest cities. It was discovered in 2001 on a sheep farm in the Jack Hills region north of Perth. It was turned over to scientists to date using newer methods that replaced often inaccurate and faulty ones, such as observing radioactive decay levels in uranium atoms. To attempt the most accurate dating possible, scientists used a method known as atom-probe tomography, designed to make individual lead atoms visible to scientists so they can obtain the ratio of lead isotopes to each other. Lead, which is an element, has 20 isotopes, 16 of which are radioactive. The tiny crystal, measuring 400 micrometers, is naturally red; when a ray of electrons is fired at it, it becomes a deep blue color.
A commonly held belief by scientists is that life could not exist on Earth until approximately 4.3 billion years ago. The discovery of the crystal’s age backed up the long-held theory by scientists that liquid water existed early enough in Earth’s formation as a planet to allow tiny microbial particles to sustain life 4.3 billion years ago. The discovery could mean that the zircon was formed just a few million years after a newborn Earth was melted down into molten rock by a violent collision with an asteroid the size of Mars, an event that led to the formation of the moon. The crystal also lends credibility to scientists’ theories that the period following that collision, known as the “Hadean Eon”, was far shorter than previously thought. The Hadean Eon was characterized by uninhabitable conditions and the formation of the atmosphere, oceans, and the stabilizations of Earth’s layers. It encompasses approximately the first 600 million years of Earth’s existence.