Oldest Earth - Jack Hills Zircon
"The only physical evidence from the earliest phases of Earth’s evolution comes from zircons." ~ John Valley, Geoscientist
This specimen is a small piece of the Jack Hills formation north of Perth in Western Australia (pictured above). The rough, sedimentary layers of the Jack Hills formation are 3.3 billion years old, but they also contain much older zircon crystals across a range of time from 3.6 to nearly 4.4 billion years old. The specimen was collected in accordance with Australia's cultural heritage and mining laws.
As pictured, the specimen measures 1x1 cm and is enclosed inside an acrylic specimen jar. The jar is enclosed inside a classic, glass-topped riker display case. A small information card is also enclosed.
About the Early Earth
Named for the fiery lord of the ancient greek underworld, the Hadean Eon (4.5-3.95Ga) describes a time when the Earth's surface was subject to widespread volcanism and continuous collisions with remnant objects in the chaotic early solar system.
It would seem an inhospitable place for water, let alone life. Yet our scientific understanding has changed quite a bit since the Hadean was first described in 1972.
Above: An Artistic Rendering of the Earth during the Hadean
We've learned that Earth must have possessed a significant amount of water during its early formation, and even though the heat was intense the atmospheric pressure of carbon dioxide kept water on the surface from boiling off. We also know that plate tectonics, the grinding of the crust, began during this time. Together these forces helped scrub the atmosphere of carbon dioxide and other greenhouse gases, leading to cooler surface temperatures and conditions favorable for life.
This history has been revealed by studying the chemical makeup of small crystals called zircons. Zircons are quite common in the crust of Earth. They are shed through the process of erosion once igneous rocks reach the surface, at which point the zircons are incorporated into new sedimentary layers.
Above: False color image of the oldest known zircon found in the Jack Hills formation. Estimated age 4,374,000,000 years old. (Source: Valley, John W., et al. "Hadean Age for a Post-magma-ocean Zircon Confirmed by Atom-probe Tomography." Nature Geoscience 7.3 (2014): 219-223.)
In addition to being the oldest known samples of Earth's crust, the zircons of the Jack Hills formation also contain water and the earliest suggestions of life in the form of biogenic carbon. As the science around this topic evolves, it may push back the starting point for life on Earth by hundreds of millions of years.