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Encyclopedia > Paleoarchean
Paleoarchean era
Geologic timescale of the Precambrian
(millions of years ago)

(expand) The geologic timescale is used by geologists and other scientists to describe the timing and relationships between events that have occured during the history of the Earth. ... The Precambrian or Cryptozoic is the period of the geologic timescale from the formation of Earth around 4500 million years before the present (BP) to the evolution of abundant macroscopic hard-shelled fossils, which marked the beginning of the Cambrian, some 542 million years BP. Remarkably little is known about...

The Paleoarchean is a geologic era within the Archaean. It spans the period of time 3.6 to 3.2 billion years ago—the period being defined chronometrically and not referenced to a specific level in a rock section on Earth. ERA is an abbreviation for several different things, including: the Equal Rights Amendment, a proposed, but unratified, Constitutional amendment in United States Earned run average, a baseball statistic Engine Room Artificer Education Reform Act Engineering Research Associates, a pioneering computer firm from the 1950s Academy of European Law Trier Explosive... The Archean is a geologic eon; it is a somewhat antiquated term for the time span between 2500 million years before the present and 3800 million years before the present. ...

Archaean eon
Eoarchean Paleoarchean Mesoarchean Neoarchean

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Selected Abstracts (689 words)
There are five main geocronological units in the Precambrian history of the Ukrainian Shield: the Paleoarchean, the Mesoarchean, the Neoarchean, and the Paleoproterozoic (the last unit is subdivided into two sub-units: the Paleoproterozoic-I, and the Paleoproterozoic-II).
The Paleoarchean (3.65-3.2 Ga) is represented by rocks of the Western-Azov, the Auly, the Dniester-Bug groups (series) of metamorphic rocks; the Novopavlivka and Gayvorone granitoid complexes.
The low age limit of the Paleoarchean was determined on the magmatic formations of ultramafic-mafic-thonalite rock association of the Novopavlivka complex, and the high one – on enderbites of the Gayvorone and Novopavlivka complexes.
v23d in sm04 (2841 words)
Estimates for the rate of crustal growth and recycling during Paleoarchean time are tied to the analysis of these ancient crustal remnants.
Sm-Nd and U-Pb isotope data indicate that a fragment of Meso- to Paleoarchean crust occurs in the Churchill craton, on the north shore of Lake Athabasca, Saskatchewan (Canada).
This shear zone may represent the surface expression of a suture between the Meso- to Paleoarchean and younger (Neoarchean?) crust.
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