View source for Earth:Zirconian

{{short description|Proposed second era of the Hadean eon}}
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| style="text-align:center;background-color:{{Period color|hadean}}" |'''Zirconian Era'''<br />''4404–4031 million years ago''
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The '''Zirconian''' is  the second [[Earth:Era (geology)|Era]] within the [[Earth:Hadean|Hadean]] [[Earth:Eon (geology)|Eon]] in a proposed revision of the [[Earth:Precambrian|Precambrian]] time scale.<ref>{{cite journal | last=Gradstein | first=Felix M. | last2=Ogg | first2=James G. | last3=Hilgen | first3=Frits J. | title=On The Geologic Time Scale | journal=Newsletters on Stratigraphy | publisher=Schweizerbart | volume=45 | issue=2 | date=1 March 2012 | issn=0078-0421 | doi=10.1127/0078-0421/2012/0020 | pages=171–188}}</ref> It lasted 373 million years from the end of the [[Earth:Chaotian (geology)|Chaotian]] Era {{Ma|4404}} to the beginning of [[Earth:Eoarchean|Eoarchean]] Era {{Ma|4031}}. The Zirconian follows the Chaotian Era and its beginning is chronometrically set at 4.404 ± 0.008 Gya. This corresponds to the age of the first occurrence of [[Earth:Hadean zircon|Hadean zircon]]s in the Jack Hills in Western Australia (Yilgarn craton). The end of the Zirconian Era and the transition to the Acastan Period (the earliest period of the [[Earth:Archean|Archean]] Eon and [[Earth:Eoarchean|Eoarchean]] Era) occurred with the appearance of the [[Earth:Acasta Gneiss|oldest rock]] at 4.031 ± 0.003 Gya.

== Etymology ==
[[File:Zircon microscope.jpg|left|150px|thumb|[[Chemistry:Zircon|Zircon]] crystal with magmatic Anwachssäumen under the light microscope]]
The term ''Zirconian'' is derived from the mineral [[Chemistry:Zircon|zircon]], since it is the only substance that is preserved from this early period. An alternative proposal for the name of this era is "'''Jack Hillsian Era'''".

== Meaning ==
The first 196 million years after the formation of [[Earth:Age of Earth|Earth]], left no solid trace, except for the formation of the [[Astronomy:Moon|Moon]]. This time is termed the [[Earth:Chaotian (geology)|Chaotian]] Era. The first datable solid Earth minerals, zircons, mark the start of the Zirconian Era. The oldest known crystal could be dated to 4,404 ± 8 [[Physics:Mya (unit)|Mya]].<ref>{{cite journal |last=Wilde |first=SA | year = 2001 | title = Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gya ago | journal = Nature | volume = 409 | issue = 6817 | pages = 175-178 |display-authors=0}}</ref> It was in metasedimentary rock on Erawandoo Hills in the Jack Hills of [[Earth:Narryer Gneiss Terrane|Narryer Gneiss Terrane]] in Western Australia. The 4.4 Gya is the limiting age, and zircons this old are very rare. But from 4.2 to 4.1 Gya they are already common. The bulk of the zircons in Narryer Gneiss Terrane date much later, from 3.75 to 3.5 Gya.

== Occurrence ==
The [[Chemistry:Zircon|zircon]]s are limited only to Archean [[Earth:Craton|craton]]s. In the Yilgarn craton [[Earth:Quartzite|quartzite]]s of Southern Cross Terrane also contains zircons with an age of 4.35-3.13 Gya).<ref>{{cite journal | last=Wyche | first=S. | last2=Nelson | first2=D. R. | last3=Riganti | first3=A. | title=4350-3130 Ma detrital zircons in the Southern Cross Granite-Greenstone Terrane, Western Australia: implications for the early evolution of the Yilgarn Craton | journal=Australian Journal of Earth Sciences | publisher=Wiley | volume=51 | issue=1 | year=2004 | issn=0812-0099 | doi=10.1046/j.1400-0952.2003.01042.x | pages=31–45 |display-authors=1}}</ref>

Possibly the Nuvvuagittuq Greenstone Belt of the [[Earth:Superior Craton|Superior Craton]] is of Zirconian age, its proposed age of 4.28 Gya is however still controversial. The end of the Zirconian Era is at 4.031 Gya, marked by the [[Earth:Acasta Gneiss|Acasta Gneiss]] of Slave craton and it is likely that its [[Earth:Protolith|protolith]] is older. In 2006, a single zircon crystal in Acasta Gneiss was dated to 4.2 Gya<ref>{{cite journal | last=Iizuka | first=Tsuyoshi | last2=Horie | first2=Kenji | last3=Komiya | first3=Tsuyoshi | last4=Maruyama | first4=Shigenori | last5=Hirata | first5=Takafumi | last6=Hidaka | first6=Hiroshi | last7=Windley | first7=Brian F. | title=4.2 Ga zircon xenocryst in an Acasta gneiss from northwestern Canada: Evidence for early continental crust | journal=Geology | publisher=Geological Society of America | volume=34 | issue=4 | year=2006 | issn=0091-7613 | doi=10.1130/g22124.1 | page=245 |display-authors=1}}</ref>

== References ==

{{reflist | 30em}}

{{geological history}}

[[Category:Hadean]]
[[Category:Geological eras]]

{{Sourceattribution|Zirconian|1}}