The Jack Hills are a range of hills in Mid West

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to t ...

. They are best known as the source of the oldest material of terrestrial origin found to date: Hadean zircons that formed around 4.39 billion years ago. These zircons have enabled deeper research into the conditions on Earth in the

Hadean The Hadean ( ) is a geologic eon of Earth history preceding the Archean. On Earth, the Hadean began with the planet's formation about 4.54 billion years ago (although the start of the Hadean is defined as the age of the oldest solid materia ...

eon. In 2015, "remains of biotic life" were found in 4.1 billion-year-old rocks there. Early edition, published online before print. According to one of the researchers, "If life arose relatively quickly on Earth...then it could be common in the

universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the univers ...

Geography

They are located on the border of the Shire of Murchison and the Shire of Meekatharra, south of the Murchison River, about north of

Perth Perth is the capital and largest city of the Australian state of Western Australia. It is the fourth most populous city in Australia and Oceania, with a population of 2.1 million (80% of the state) living in Greater Perth in 2020. Perth is ...

Geology

The Jack Hills are located in the

Narryer Gneiss Terrane The Narryer Gneiss Terrane is a geological complex in Western Australia that is composed of a tectonically interleaved and polydeformed mixture of granite, mafic intrusions and metasedimentary rocks in excess of 3.3 billion years old, with t ...

of the

Yilgarn Craton The Yilgarn Craton is a large craton that constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts. Zircon grains in the Jack Hills, Narryer Terrane have b ...

, and comprise an long northeast-trending belt of folded and

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

supracrustal rocks.

Sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

siliciclastic rocks, interpreted as

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...

- delta deposits, are the major lithology. Minor

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...

ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...

rocks and

banded iron formation Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness ...

(BIF) are also found in the sequence. The overall sequence is generally considered to be a granulite gneiss, which has undergone multiple deformations and multiple metamorphic episodes. The protolith age of the Narryer Gneiss Terrane is variable, but generally considered to be in excess of 3.6 Ga (billion years).

Oldest zircons on Earth

Detrital

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...

s with ages greater than 4 billion years old have been found in these rocks, and a 4,404 ± 8 million year old zircon was found at Erawandoo Hill; this is the oldest dated material originating on Earth; the date is in the

Cryptic era Cryptic may refer to: In science: * Cryptic species complex, a group of species that are very difficult to distinguish from one another * Crypsis, the ability of animals to blend in to avoid observation * Cryptic era, earliest period of the Earth ...

of the

eon. They were found within a unit of the supracrustal sequence, a metamorphosed

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** ...

considered to have an age ~3.0 Ga. Given the detrital nature of the rock unit, the zircons are sourced from pre-existing rocks which were then weathered and the resultant sediment deposited as sedimentary rock. The zircons and various aspects of their geochemistry provide evidence for the existence of continental-type crust on the surface of Earth during the Hadean eon, contrasting with earlier ideas on the earliest phase of Earth's history. Additionally, oxygen isotopic ratios in the zircons provide evidence for the presence of liquid water on the surface, if not a water ocean; also contrasting with earlier ideas on Earth's history. The hypothesis of humid and cool conditions before the

Late Heavy Bombardment The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypot ...

has been promoted as

cool early Earth The Hadean ( ) is a geologic eon of Earth history preceding the Archean. On Earth, the Hadean began with the planet's formation about 4.54 billion years ago (although the start of the Hadean is defined as the age of the oldest solid material ...

Economic geology

The Jack Hills banded iron formation (BIF) is the site of a non-operating minor

iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the ...

mine owned by Mitsubishi Development Pty Ltd, a wholly owned subsidiary of

Mitsubishi Corporation is Japan's largest trading company (sogo shosha) and a member of the Mitsubishi keiretsu. As of 2022, Mitsubishi Corporation employs over 80,000 people and has ten business segments, including finance, banking, energy, machinery, chemical ...

, which in the past exported up to 3 million tonnes per annum of high grade detrital

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

iron ore via the port of

Geraldton Geraldton ( Wajarri: ''Jambinu'', Wilunyu: ''Jambinbirri'') is a coastal city in the Mid West region of the Australian state of Western Australia, north of the state capital, Perth. At June 2018, Geraldton had an urban population of 37,648. ...

. Other companies operating in the area are also planning major magnetite BIF-based iron ore mines.

Conservation

Because of their importance as a geology research site, the Jack Hills were nominated to the

Register of the National Estate The Register of the National Estate was a heritage register that listed natural and cultural heritage places in Australia that was closed in 2007. Phasing out began in 2003, when the Australian National Heritage List and the Commonwealth Herita ...

in 2003. , they had an "Interim Listing", which means they have been formally proposed for inclusion in the Register. In July 2020 it was announced that the Erawondoo Hill site has been permanently included in the National Heritage List.

IUGS geological heritage site

In respect of being the 'largest ''in situ'' repository of the oldest terrestrial crystals known to exist on Earth', the

International Union of Geological Sciences The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to international cooperation in the field of geology. About The IUGS was founded in 1961 and is a Scientific Union member of the Int ...

(IUGS) included the 'Archean zircons of Erawondoo Hill' in its assemblage of 100 'geological heritage sites' around the world in a listing published in October 2022. The organisation defines an IUGS Geological Heritage Site as 'a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history.'

References

{{Commons category Mid West (Western Australia) Hills of Australia Geology of Western Australia Precambrian Oceania First 100 IUGS Geological Heritage Sites