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Zircon is a mineral that has been found in Western Australia, specifically in the Jack Hills region, 800km north of Perth. Zircons are the oldest known materials on the planet, dating back 4.4 billion years, and have been used to determine the age of ancient rocks. They have also provided evidence for the existence of continental-type crust on the surface of the Earth during the Hadean eon, as well as the presence of liquid water on the surface.
| Characteristics | Values |
|---|---|
| Location | Jack Hills, Western Australia |
| Distance from Perth | 800 kilometres north |
| Date of discovery | 2014 |
| Zircon crystal age | 4.4 billion years |
| Zircon crystal age (precise) | 4.404 billion years |
| Zircon crystal sample name | 01JH36-69 |
| Zircon crystal size | Microscopic |
| Study author | Prof. John Valley |
| Study author (alternative name) | Prof. Valley |
| Study author (co-author) | Prof. Mark Harrison |
| Study technique | Atom-probe tomography |
| Study technique (secondary) | Secondary ion mass spectrometry |
| Study publication | Nature Geoscience |
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What You'll Learn
Zircon is found in Western Australia's Jack Hills region
The discovery of these ancient zircons has provided valuable insights into the early history of our planet. By studying their chemical composition and structure, scientists have been able to determine that the early Earth was likely cooler and wetter than previously thought. This finding contradicts earlier theories and the asteroid-crater evidence on the Moon, suggesting a "cool early Earth" hypothesis. The presence of liquid water on the surface, or even a water ocean, is indicated by oxygen isotopic ratios in the zircons, further supporting this hypothesis.
The Jack Hills zircons have also enabled groundbreaking research into the conditions on Earth during the Hadean eon, a period of time that began around 4.4 billion years ago, shortly after the formation of the planet. Scientists have found evidence of continental-type crust on the surface of the Earth during this ancient time, which contrasts with earlier ideas about the earliest phase of our planet's history. Additionally, the study of zircons has provided valuable insights into the thermal history of the Earth.
The durability of zircons is remarkable, as they have been recycled through countless generations of rock. This durability makes them an excellent tool for determining the age of ancient rocks. The Jack Hills zircons, in particular, have played a crucial role in setting back the Earth clock and strengthening the theory of a cool early Earth. They offer a window into the past, allowing scientists to piece together the puzzle of our planet's formation and evolution.
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Jack Hills is 800km north of Perth
The Jack Hills are located around 800 kilometres north of Perth, in Western Australia. They are best known as the source of the oldest material of terrestrial origin found to date: Hadean zircons that formed around 4.4 billion years ago. These zircons have enabled researchers to learn more about the conditions on Earth during the Hadean eon, the first 600 million years of Earth's history.
The Jack Hills banded iron formation (BIF) is the site of a non-operating minor iron ore mine owned by Mitsubishi Development Pty Ltd. The site has been recognised for its geological significance, being included on the Australian National Heritage List and the International Union of Geological Sciences' list of 100 'geological heritage sites' around the world.
The Jack Hills formation is around 3.3 billion years old, but it also contains much older zircon crystals. These zircons are dated to a range of times from 3.6 to nearly 4.4 billion years old. The discovery of these ancient zircons has provided evidence of the existence of a hydrosphere and continental crust on the Earth around 4 Gyr ago.
The Jack Hills are located within the Narryer Gneiss terrane of the Yilgarn craton, comprising an 80-kilometre-long northeast-trending belt of folded and metamorphosed supracrustal rocks. The major lithology of the hills is sedimentary siliciclastic rocks, interpreted as alluvial fan-delta deposits.
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The zircon crystal is 4.4 billion years old
Zircons are one of the toughest minerals on the planet. They are often referred to as crystalline time capsules that offer a window into the conditions of early Earth. In 2001, a zircon crystal was discovered in the Jack Hills of Western Australia, around 800 kilometres north of Perth. This crystal, named 01JH36-69, has been dated to around 4.4 billion years ago, making it the oldest known fragment of the Earth.
The Jack Hills zircon crystal is a tiny fragment, only 400 micrometers long, which is just a little larger than a house dust mite or about four human hairs. It was found in metamorphosed sandstone and was dated using uranium-lead radioactive dating. This method involves measuring the ratio of uranium to lead in the sample, as uranium radioactively decays into lead at a known rate. However, there have been concerns over the accuracy of using this method to date zircon crystals, as the lead atoms may have moved within the crystal over time, leading to a faulty estimate of its age.
To address this issue, researchers used a new technique called atom-probe tomography, which allowed them to image individual atoms of lead and determine their isotope ratio. They found that the lead atoms in the Jack Hills zircon had formed clumps about 1 billion years after the crystal's formation, but these clusters were small enough that they did not affect the analysis. This confirmed that the zircon crystal was indeed approximately 4.4 billion years old.
The discovery of the 4.4 billion-year-old zircon crystal has significant implications for our understanding of early Earth. It provides evidence that the Earth's crust first formed at least 4.4 billion years ago, and that the planet was cool enough for liquid water, oceans, and a hydrosphere not long after its formation. This supports the theory of a "cool early Earth," which contradicts the previous view of a fiery hellscape under constant meteoric assault.
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It's the oldest known material formed on Earth
Zircon crystals, found in Western Australia's Jack Hills region, are the oldest known materials formed on Earth. The Jack Hills are a range of hills in Mid West Western Australia, located about 800 kilometres north of Perth. The zircon crystals from this region have been dated to around 4.4 billion years ago, providing valuable insights into the early history of our planet.
The discovery of these ancient zircons has significant implications for our understanding of the Earth's formation and early conditions. The presence of zircons offers evidence for the existence of continental-type crust on the surface of the Earth during the Hadean eon, which was the earliest phase of the planet's history. This challenges traditional ideas about the early Earth, suggesting that it was not a hellish, dry, boiling planet, but rather a cool, humid environment with the potential for life.
The study of zircons and their geochemistry has provided crucial clues about the conditions on early Earth. For example, oxygen isotopic ratios in the zircons indicate the presence of liquid water, if not a water ocean, during the Hadean eon. This supports the hypothesis of a "cool early Earth" theory, where temperatures were low enough to support liquid water, oceans, and a hydrosphere not long after the planet's crust formed.
Additionally, the analysis of zircons has offered insights into the origin of life. In 2015, scientists discovered bits of graphite, which is pure carbon, in a 4.1-billion-year-old zircon from the Jack Hills. This graphite is believed to be of biological origin, providing evidence that simple life forms may have existed on early Earth. The study of zircons and their inclusions, such as graphite, helps us understand the evolution of life and the conditions that supported it.
The durability of zircon minerals makes them invaluable for dating ancient rocks and learning about the Earth's history. Their crystal structure, with specific sites for atoms of particular sizes and charges, allows for precise dating using uranium-lead radioactive dating techniques. This has enabled scientists to confirm the validity of their findings and deepen our understanding of the Earth's formation and evolution.
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It's used to determine the age of ancient rocks
Zircon crystals, or zirconium silicate, have become a crucial tool for geologists to determine the age of ancient rocks. They are the oldest known materials on Earth, offering insights into the planet's history as far back as 4.4 billion years ago when the Earth was a mere 160 million years old. This is achieved through uranium-lead radioactive dating, which involves examining the ratio of uranium to lead in a zircon sample. Uranium decays into lead at a known rate, allowing scientists to calculate the age of the crystal.
Zircons are highly resistant to chemical changes, making them ideal for dating ancient rocks. They are also small, roughly the size of a grain of sand, and are often found in rivers and ancient lake beds. Researchers collect, crush, and sift through rock samples to obtain zircon crystals for analysis. The development of laser technology and more sensitive analytic instruments has made zircon dating more precise and accessible.
The crystal structure of zircon is unique in that it has specific sites that can accommodate atoms of particular sizes and charges. Uranium atoms are concentrated in these sites, while lead atoms are excluded during the crystal growth process. As uranium decays into lead, it emits alpha particles, causing the newly formed lead atoms to move to other parts of the crystal. This process can impact the perceived age of the zircon, with some areas appearing younger or older than they actually are.
To address this challenge, scientists have employed atom-probe tomography, which involves determining the mass of individual lead atoms in the sample. In the case of the Jack Hills zircon in Western Australia, the lead atoms were found to be clumped together, validating the accuracy of the dating method. This discovery provided valuable insights into the early Earth, supporting the theory of a ""cool early Earth" with temperatures low enough to support liquid water, oceans, and a hydrosphere.
By studying zircons, researchers can piece together the origin stories of planets, understand the formation of continents, and even discover valuable mineral deposits. Zircon dating has become an indispensable tool in geochronology, helping scientists unravel the mysteries of Earth's distant past and gain a deeper understanding of our planet's evolution.
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Frequently asked questions
Zircon is found in Western Australia, in the Jack Hills, 800 kilometres north of Perth.
The zircons found in Australia are around 4.4 billion years old. They are the oldest known material of any kind formed on Earth.
The discovery of zircons in Australia has provided valuable insights into the early history of our planet. They offer evidence of the existence of continental-type crust and the presence of liquid water on the surface during the Hadean eon, suggesting that the early Earth may have been cooler and more humid than previously thought.
Zircon crystals have a unique crystal structure with specific sites that can accommodate atoms of a particular size and charge. This results in the concentration of uranium atoms and the exclusion of lead atoms, making them exceptionally resistant to chemical changes.
