|List||Register of the National Estate (Non-statutory archive)|
|Legal Status||Interim List (28/10/2003)|
|Place File No||5/15/183/0011|
|Statement of Significance|
Very little is known or understood about the Earth's early development. During the Hadean Eon (between 3800 and 4550 million years (my) ago), the Earth was forming in a hostile environment, vastly different to that of present. As no rocks have been found from the first 500 million years of the Hadean Eon, much of what is known from this time has been learnt through the analysis of ancient crystals from the Jack Hills region of Western Australia.
Small crystals of zircon found in a chert-pebble conglomerate at Erawondoo Hill within the Jack Hills area are older than any other material identified on Earth. Approximately 10 percent of the zircon crystals analysed so far are over 4000 my old, with the oldest having been dated to 4404 my.
The zircon crystals found at Jack Hills are not only significant for their age, they have also provided geochemical information that has led to a better understanding of the geological processes that occurred during the initial formation of the Earth. The oldest zircon crystal has extended the knowledge of the Earth's development back a further 130 million years from that sourced from the previous oldest known material.
By analyzing the oxygen 18 to oxygen 16 isotope ratio present within the oldest known Jack Hills zircon crystal, scientists now know that the earth possessed liquid water in some form as early as 4404 mya. The high oxygen isotope ratios also represent the earliest evidence of a continental crust on the Earth and place evidence of terrestrial material to within 160 million years of when it is generally estimated that the Earth first formed.
Jack Hills continues to be an important research site for investigation of the Earth's early environment. The presence of liquid water at 4400+ my ago has placed constraints on what was previously thought concerning the timeframe of the Earth's cooling history, the development of oceans and continents, as well as the creation of the moon.
It is possible that Indigenous and non-Indigenous cultural values of National Estate significance may exist in this place. As yet, the AHC has not identified, documented nor assessed these values.
|Official Values Not Available|
The Jack Hills are situated approximately 800 km north of Perth near the Murchison River. The hills consist of steeply dipping metamorphosed Precambrian rocks which project above the surrounding landscape because the metamorphic sediments of which they are composed are more resistant to weathering than the surrounding gneiss and granite.
The Jack Hills meta-sedimentary belt is approximately 70km in length and is believed to be between 3100 and 3200 million years old. The hills are within the Narryer Gneiss Terrane of the Yilgarn Craton and are composed of metamorphosed basalts, ultramafic rocks (igneous rocks that contain low amounts of quartz and feldspars), cherts, banded iron formation and rocks that are composed of weathered material sourced from older rocks known as clastic meta-sediments. Within these metamorphosed sediments, geologists have found crystals of the mineral zircon that are older than any other known material on Earth.
Zircon is a very durable mineral that can resist weathering and extreme geological conditions and as such is often found as remnant survivors in younger sedimentary or metamorphic rocks. Zircon is unique in that it is one of the only minerals that over a long period of time, can preserve chemical information that indicates what conditions were like when the crystals were originally formed.
During formation, zircon crystals trap unstable radioactive material such as uranium in their crystalline structure. As the rate by which uranium decomposes into lead is well understood, measuring the ratio between the amount of uranium and lead present within the zircon enables geologists to accurately determine how old the crystal is.
The Narryer Gneiss Terrane has been known to contain ancient material since the 1980s when zircons between 4100 and 4180 million years (my) old were discovered at nearby Mount Narryer. Although zircon crystals were first discovered in a conglomerate at Jack Hills in 1986, it was not until the late 1990's that a new research project focused attention on documenting the zircon record of the area. The proportion of old zircon crystals in the Jack Hills conglomerate is between 12 and 20% which is about five times higher than at Mt Narryer.
The zircon crystals found at Jack Hills provide information on a period of the Earth's history before 4100 my of which there is little remaining evidence. The Earth's oldest known rocks, dated at 4060 my, are from the Acasta Gneiss on the Acasta River in Slave Province of the Northwestern Territories, Canada.
The chemical analysis of the Jack Hills zircon crystals has indicated that the Earth had surface water and a hydrosphere much earlier than previously thought. Oxygen isotopes found within zircon crystals are a sensitive, temperature-dependant indicator of liquid and solid interactions in the Earth's crust. Zircon crystals with high oxygen 18 to oxygen 16 isotope ratios such as some of those found at Jack Hills, can only be formed if crustal material interact with surface or near surface water at low temperatures. Previous to this discovery, the earliest evidence of water on earth is from banded iron formations in Greenland that have been dated to approximately 3850 my.
That the zircon crystals formed within a continental (surface) crust implies that the Earth had at least a partially stabilised terrestrial surface at this early stage of its development. It is thought that the zircon crystals from Jack Hills are products of an ancient crust that developed between periods of intense meteor bombardment. Previous to the discovery of the age and geochemical properties of the ancient Jack Hills zircons, it was generally thought it would not have been possible for the Earth to have a terrestrial surface during the early stages of its development due to the constant bombardment of the earth by meteoritic material in the solar system.
The discovery that stable, low temperature conditions may have existed for periods of time at such an early stage in the Earth's development also has wider implications for the study of early life. As low temperatures and the presence of liquid water are the requirements for life, the discovery of both in the geochemistry of the Jack Hills zircon crystal has led scientists to suggest the possibility of life occurring on Earth at least 400 my earlier than was previously thought possible.
|History Not Available|
|Condition and Integrity|
The Jack Hills area is contained within three pastoral stations: Mileura Station, Nookawarra Station and Beringarra Station. Although the area is generally not stocked with sheep or cattle, the hills do provide a refuge for feral goats that are a pest problem.
Very little fauna survey work has been undertaken at Jack Hills and apart from birds no other fauna groups have been officially recorded in the area. It is likely that Jack Hills provides habitat for a range of small reptiles such as skinks, blind snakes and dragons as well as small rodents and carnivorous marsupials.
The predominant vegetation type within the Jack Hills area is an association of minirichi ACACIA GRASBYI and mulga A. ANEURA. Other species that have been found in the area include EREMOPHILA LATROBEI, E. OPPOSITIFOLIA, SCAEVOLA SPINESCENS and OLEARIA OBOVATUS. The vegetation is generally weed free and is mostly in good condition.
Research continues on zircon-bearing material taken from the area and a detailed geological survey of the area is currently taking place.
About 3100ha, 165km north-west of Cue, being an area bounded
by a line commencing at AMG point 951080, then via straight lines joining the
following AMG points consecutively; 031079, 031053, 950028, then directly to
the point of commencement.. |
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Curtin University of Technology (2001). World's oldest crystal tells tale of hospitable early earth. Available from:
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Myers J.S. (1990a). Western gneiss terrain in geology and mineral resources of Western Australia. Geological Survey of West. Australia Mem.3.
Peck W.H., Valley J.W, Wilde. S.A. and Graham C.H. (2001). Oxygen isotope ratios and rare earth elements in 3.3 to 4.4 Ga zircons: Ion microprobe evidence for high d18O continental crust and oceans in the Early Archean. Geochimica et Cosmochimica Acta 65: 22, p4215 - 4229.
Pidgeon R.T., Wilde S.A. and Compston W. (1990). Timing of granite activity associated with the Archaean Jack Hills metasedimentary belt, Yilgarn Craton, Western Australia in 3rd Archaean Conference Perth 1990 Extended Abstracts Vol. Geoconferences (W.A.) Inc. Perth.
Sankaran A.V. (2003). The Hadean earth - a veritable hell, or haven for early life? Answer from >4 billion year old zircons. Current Science Vol 84 No. 2, p134 - 136.
Valley J.W., Peck W.H., King E.M. and Wilde S.A. (2002). A cool early Earth. Geology 30, p351-354.
Wilde S.A. and Pidgeon R.T. (1990). The Jack Hills Sedimentary Belt in J.S. Myers, S.E. Ho & J E. Glover (Eds) 'Excursion guide to Narryer Gneiss Complex', 3rd Internat. Archaean Conference Geol. Dept. & University Extension, Univ. West. Australia.
Wilde, S.A., Valley, J.W. Peck, W.H. and Graham, C.M. (2001). Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4gyr ago. Nature Vol 409, p175 - 178.
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Wilde S. A., Valley J. W., Peck W. H. and Graham C. M. (2001). Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature Vol 409, p175 - 178.
Report Produced Wed Jul 30 02:28:47 2014