Editing Age of Earth (section)

====Use of meteorites====
An age of 4.55 ± 0.07 billion years, very close to today's accepted age, was determined by [[Clair Patterson|Clair Cameron Patterson]] using uranium–lead isotope dating (specifically [[lead–lead dating]]) on several meteorites including the [[Canyon Diablo (meteorite)|Canyon Diablo meteorite]] and published in 1956.<ref name="Patterson">{{cite journal | last=Patterson | first=Claire | title=Age of meteorites and the earth | journal=Geochimica et Cosmochimica Acta | url=http://es.ucsc.edu/~rcoe/eart206/Patterson_AgeEarth_GeoCosmoActa56.pdf | date=1956 | volume=10 | issue=4 | pages=230–237 | access-date=2009-07-07 | doi=10.1016/0016-7037(56)90036-9 | bibcode=1956GeCoA..10..230P | url-status=live | archive-url=https://web.archive.org/web/20100621045217/http://es.ucsc.edu/%7Ercoe/eart206/Patterson_AgeEarth_GeoCosmoActa56.pdf | archive-date=2010-06-21 }}</ref> The quoted age of Earth is derived, in part, from the Canyon Diablo meteorite for several important reasons and is built upon a modern understanding of cosmochemistry built up over decades of research.
[[File:Paterson isochron animation.gif|thumb|left|upright=1.6|Lead isotope isochron diagram showing data used by Patterson to determine the age of Earth in 1956.]]Most geological samples from Earth are unable to give a direct date of the formation of Earth from the solar nebula because Earth has undergone differentiation into the core, mantle, and crust, and this has then undergone a long history of mixing and unmixing of these sample reservoirs by [[plate tectonics]], [[weathering]] and [[hydrothermal circulation]].

All of these processes may adversely affect isotopic dating mechanisms because the sample cannot always be assumed to have remained as a closed system, by which it is meant that either the parent or daughter [[nuclide]] (a species of atom characterised by the number of neutrons and protons an atom contains) or an intermediate daughter nuclide may have been partially removed from the sample, which will skew the resulting isotopic date. To mitigate this effect it is usual to date several minerals in the same sample, to provide an [[isochron]]. Alternatively, more than one dating system may be used on a sample to check the date.

Some meteorites are furthermore considered to represent the primitive material from which the accreting solar disk was formed.<ref>{{cite conference | author=Carlson, R. W.| author2=Tera, F.
 | title=Lead–Lead Constraints on the Timescale of Early Planetary Differentiation
 | book-title=Conference Proceedings, Origin of the Earth and Moon | page=6
 | publisher=Lunar and Planetary Institute
 | date=December 1–3, 1998
 | location=Houston, Texas | url=http://www.lpi.usra.edu/meetings/origin98/pdf/4066.pdf |access-date=2008-12-22 | archive-url= https://web.archive.org/web/20081216214311/http://www.lpi.usra.edu/meetings/origin98/pdf/4066.pdf| archive-date= 16 December 2008 | url-status= live}}</ref> Some have behaved as closed systems (for some isotopic systems) soon after the solar disk and the planets formed.{{citation needed|date=March 2015}} To date, these assumptions are supported by much scientific observation and repeated isotopic dates, and it is certainly a more robust hypothesis than that which assumes a terrestrial rock has retained its original composition.

Nevertheless, ancient [[Archean|Archaean]] lead [[ores]] of [[galena]] have been used to date the formation of Earth as these represent the earliest formed lead-only minerals on the planet and record the earliest homogeneous lead–lead isotope systems on the planet. These have returned age dates of 4.54 billion years with a precision of as little as 1% margin for error.<ref>Dalrymple (1994) pp. 310–341</ref>

Statistics for several meteorites that have undergone isochron dating are as follows:<ref name="BGDarymple">{{cite book
 | author=Dalrymple, Brent G.
 | title=Ancient Earth, Ancient Skies: The Age of the Earth and Its Cosmic Surroundings
 | url=https://archive.org/details/ancientearthanci0000dalr
 | url-access=registration
 | date=2004
 | publisher=[[Stanford University Press]]
 | isbn = 978-0-8047-4933-6
 | pages = [https://archive.org/details/ancientearthanci0000dalr/page/147 147], 169
}}
</ref>

{| <!-- is [[Figure space]], the width of one digit. -->
!colspan=4 align=left| 1. St. Severin (ordinary chondrite)
|-
|width=1em| || 1. || Pb-Pb isochron || 4.543 ± 0.019 billion years
|-
| || 2. || Sm-Nd isochron || 4.55  ± 0.33 billion years
|-
| || 3. || Rb-Sr isochron || 4.51  ± 0.15 billion years
|-
| || 4. ||| Re-Os isochron || 4.68  ± 0.15 billion years
|-
!colspan=4 align=left| 2. Juvinas (basaltic achondrite)
|-
| || 1. || Pb-Pb isochron || 4.556 ± 0.012 billion years
|-
| || 2. || Pb-Pb isochron || 4.540 ± 0.001 billion years
|-
| || 3. || Sm-Nd isochron || 4.56  ± 0.08 billion years
|-
| || 4. || Rb-Sr isochron || 4.50  ± 0.07 billion years
|-
!colspan=4 align=left| 3. Allende (carbonaceous chondrite)
|-
| || 1. || Pb-Pb isochron || 4.553 ± 0.004 billion years
|-
| || 2. || Ar-Ar age spectrum || 4.52  ± 0.02 billion years
|-
| || 3. || Ar-Ar age spectrum || 4.55  ± 0.03 billion years
|-
| || 4. || Ar-Ar age spectrum&nbsp; || 4.56  ± 0.05 billion years
|}