If you thought that diamonds were forever, they have absolutely nothing on the zircon of Jack Hills, Australia. Professor of geoscience at the University of Wisconsin, John Valley has confirmed that this bit of Earth’s crust is the oldest fragment of the planet ever found at 4.375 billion years old. Using a technique called “atom-probe tomography,” Valley and his fellow scientists dated the zircon with more accuracy than previous methods. Not only did they confirm the zircon’s spectacular age, but also solidified the theory that early Earth was cool and had temperatures low enough to sustain liquid water and a hydrosphere.
The crystals date back to 165 million years after the formation of the planet and were found exposed from erosion in an Australian riverbed. To determine the age of the zircon, Valley and his colleagues painstakingly measured each atom using an ion probe that concentrated on specific clusters of lead inside the fragment. This process improves upon previous methods of counting the number of lead isotopes due to the fact that uranium moves lead around as it decays, making readings more difficult to ascertain. The new technique eliminates the error that radiation damage exerts on the zircon throughout its lifespan.
The presence of such old zircons in Australia suggest that they came from water-rich, granite-like rocks that formed as the Earth cooled just 100 million years after the collision that formed the moon. Instead of the image of a fiery, lava-filled planet, the conditions were actually cool enough for surface water and continental formations not long after the molten rock congealed. Valley’s work not only solidifies impressions of early Earth, but his new method of dating old minerals could help determine the age of other ancient fragments.
Via Live Science