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The Pilbara Craton is an old and stable part of the continental lithosphere located in the
Pilbara The Pilbara () is a large, dry, thinly populated region in the north of Western Australia. It is known for its Aboriginal peoples; its ancient landscapes; the red earth; and its vast mineral deposits, in particular iron ore. It is also a g ...
region of
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 ...
. The Pilbara Craton is one of only two pristine Archaean 3.6–2.7 Ga (billion years ago) crusts identified on the Earth, along with the
Kaapvaal Craton The Kaapvaal Craton (centred on Limpopo Province in South Africa), along with the Pilbara Craton of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga (billion years ago) crust on Earth. Similarities of rock records fr ...
in
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
. Both locations may have once been part of the Vaalbara supercontinent or the continent of Ur. The eastern portion is called the
Eastern Pilbara Craton The Eastern Pilbara Craton is the eastern portion of the Pilbara Craton located in Western Australia. This region contains variably metamorphosed mafic and ultramafic greenstone belt rocks, intrusive granitic dome structures, and volcanic se ...
.


Evidence of earliest life

In May 2017, evidence of the earliest known life on land may have been found in 3.48-billion-year-old geyserite and other related mineral deposits (often found around
hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...
s and
geyser A geyser (, ) is a spring characterized by an intermittent discharge of water ejected turbulently and accompanied by steam. As a fairly rare phenomenon, the formation of geysers is due to particular hydrogeological conditions that exist only i ...
s) uncovered in the Dresser Formation in Pilbara Craton. The earliest ''direct'' evidence of life on Earth may be fossils of
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...
s
permineralized Permineralization is a process of fossilization of bones and tissues in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue. Because of the nature of the casts, perminera ...
in 3.465-billion-year-old
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
n Apex
chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...
rocks. However, the evidence for the biogenicity of these microstructures has been thoroughly debated. Originally, 11 taxa were described from a deposit thought to be located at the mouth of a river due to certain characteristics like rounded and sorted grains. Extensive field mapping and petrogenetic analysis has since shown the setting for the purported microfossils to be
hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...
and this is widely supported. Consequently, many alternative abiotic explanations have been proposed for the filamentous microstructures including carbonaceous rims around quartz spherules and rhombs, witherite self-assembled biomorphs and hematite infilled veinlets. The carbonaceous matter composing the filaments has also been repeatedly examined with
Raman spectroscopy Raman spectroscopy () (named after Indian physicist C. V. Raman) is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman ...
which has yielded mixed interpretations of results and is therefore regarded by many to be unreliable for determining biogenicity when used alone. Perhaps the most compelling argument to date is based on high spatial resolution electron microscopy like scanning and
transmission electron microscopy Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a ...
. This study concludes that the nano-scale morphology of the filaments and the distribution of the carbonaceous matter are inconsistent with a biological origin for the filaments. Instead, it is more likely that the
hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...
conditions have assisted in the heating, hydration and exfoliation of potassium micas on which barium, iron and carbonate have secondarily been adsorbed. Additional potential bioindicators from the Precambrian have been found in the region, including carbonaceous microfossils in the northeastern Pilbara Craton.


See also

*
Archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...
*
Australian Shield The Australian Shield, also called the Western Australian Shield, is a geological feature known as a shield that occupies more than half of the continent of Australia. The word shield is used because it refers to ancient, molten rock which ...
* Centralian Superbasin * Gawler Craton * Geology of Australia *
Ore genesis Various theories of ore genesis explain how the various types of mineral deposits form within Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined. Ore-genesis theories generally involve three components: sou ...
* Perth Basin * Western Plateau *
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 ...


References


Bibliography

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External links


Deformation and gold mineralisation of the Archaean Pilbara Craton, Western Australia

Stratigraphic revision of the Warrawoona and Gorge Creek Groups in the Kelly greenstone belt, Pilbara Craton,Western Australia


{{DEFAULTSORT:Pilbara Craton Cratons Geology of Western Australia Economic geology Structural geology Historical geology Bornhardts Physiographic sections Pilbara