Priscoan Eon, earliest eon of geological time, and the earliest of the three divisions of the Precambrian—the other two being the Archaean Eon and the Proterozoic Eon.
For this reason, the term is very seldom used by Earth scientists—most incorporate this early interval of geological history within the Archaean, sometimes using the term Hadean to refer to the Priscoan part of the Archaean, that is, the interval between the formation of the Earth and 4,000 million years ago.
Evidence of this bombardment has been obliterated by subsequent events in the Earth’s history, but a record of it remains on the surface of the Moon (the Priscoan Eon of Earth history is roughly equivalent to the Pre-Nectarian Period of Moon history).
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Phrases that include priscoan: priscoan aeon, priscoan eon, priscoan period
www.onelook.com /?w=priscoan (117 words)
Hadean - Wikipedia, the free encyclopedia(Site not responding. Last check: )
In the last decades of the 20th century geologists identified a few Hadean rocks from Western Greenland, Northwestern Canada and West Australia.
Harland has coined an almost synonymous term: the "Priscoan period".
The oldest known rock formations comprise somewhat altered sediments from Greenland dated around 3800MA by a volcanicdike that penetrated the rocks after they were deposited.
The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks.
Harland later coined an almost synonymous term: the "Priscoan period".
Other older texts simply refer to the eon as the Pre-Archaean, while during much of the 19th and 20th centuries, the term "Azoic" (meaning without or before life) was commonly used.
As of January, 1999, The oldest rocks found on earth are 4.031 ± 0.003 billion years old (meaning it has been that long since the molten rocks solidified and thus reset their internal clocks).
This is reported in the paper Priscoan (4.00-4.03 Ga) orthogneisses from northwestern Canada by Samuel A. Bowring & Ian S. Williams; Contributions to Mineralogy and Petrology 134(1): 3-16, January 1999.
The previous record was 3.96 billion years, set in 1989.
