Geochronology/Uranium-lead dating
Zircons contain trace amounts of uranium and thorium (from 10 ppm up to 1 wt%) and can be dated using several modern analytical techniques. Because zircons can survive geologic processes like erosion, transport, even high-grade metamorphism, they contain a rich and varied record of geological processes. Zircons are usually dated by uranium-lead (U-Pb), fission track, cathodoluminescence, and U+Th/He techniques.
Imaging the cathodoluminescence emission from fast electrons can be used as a pre-screening tool for high-resolution secondary-ion-mass spectrometry (SIMS) to image the zonation pattern and identify regions of interest for isotope analysis. This is done using an integrated cathodoluminescence and scanning electron microscope.[1]
Detrital zircon geochronology, i.e., zircons in sedimentary rock can identify the sediment source.
Zircons from Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, have yielded U-Pb ages up to 4.404 billion years,[2] interpreted to be the age of crystallization, making them the oldest minerals so far dated on Earth.
The oxygen isotopic compositions of some of these zircons have been interpreted to indicate that more than 4.4 billion years ago there was already water on the surface of the Earth.[2][3] This interpretation is supported by additional trace element data,[4][5] but is also the subject of debate.[6][7] In 2015, "remains of biotic life" were found in 4.1 billion-year-old rocks in the Jack Hills of Western Australia.[8][9] According to one of the researchers, "If life arose relatively quickly on Earth ... then it could be common in the universe."[8]
See also
[edit | edit source]References
[edit | edit source]- ↑ BV, DELMIC. "Zircons - Application Note | DELMIC". request.delmic.com. Retrieved 2017-02-10.
- ↑ 2.0 2.1 Wilde S.A., Valley J.W., Peck W.H. and Graham C.M. (2001). "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago". Nature 409 (6817): 175–8. doi:10.1038/35051550. PMID 11196637. http://www.geology.wisc.edu/%7Evalley/zircons/Wilde2001Nature.pdf.
- ↑ Mojzsis, S.J., Harrison, T.M., Pidgeon, R.T.; Harrison; Pidgeon (2001). "Oxygen-isotope evidence from ancient zircons for liquid water at the Earth's surface 4300 Myr ago". Nature 409 (6817): 178–181. doi:10.1038/35051557. PMID 11196638.
- ↑ Ushikubo, T., Kita, N.T., Cavosie, A.J., Wilde, S.A. Rudnick, R.L. and Valley, J.W. (2008). "Lithium in Jack Hills zircons: Evidence for extensive weathering of Earth's earliest crust". Earth and Planetary Science Letters 272 (3–4): 666–676. doi:10.1016/j.epsl.2008.05.032.
- ↑ "Ancient mineral shows early Earth climate tough on continents". Physorg.com. June 13, 2008.
- ↑ Nemchin, A.A., Pidgeon, R.T., Whitehouse, M.J.; Pidgeon; Whitehouse (2006). "Re-evaluation of the origin and evolution of >4.2 Ga zircons from the Jack Hills metasedimentary rocks". Earth and Planetary Science Letters 244: 218–233. doi:10.1016/j.epsl.2006.01.054.
- ↑ Cavosie, A.J., Valley, J.W., Wilde, S.A., E.I.M.F.; Valley; Wilde; e.i.m.f. (2005). "Magmatic δ18O in 4400–3900 Ma detrital zircons: a record of the alteration and recycling of crust in the Early Archean". Earth and Planetary Science Letters 235 (3–4): 663–681. doi:10.1016/j.epsl.2005.04.028.
- ↑ 8.0 8.1 Borenstein, Seth (19 October 2015). "Hints of life on what was thought to be desolate early Earth". Yonkers, NY: Mindspark Interactive Network. Retrieved 8 October 2018.
- ↑ Bell, Elizabeth A.; Boehnike, Patrick; Harrison, T. Mark et al. (19 October 2015). "Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon". Proc. Natl. Acad. Sci. U.S.A. (Washington, D.C.: National Academy of Sciences) 112: 14518–21. doi:10.1073/pnas.1517557112. ISSN 1091-6490. PMID 26483481. PMC 4664351. http://www.pnas.org/content/early/2015/10/14/1517557112.full.pdf. Retrieved 2015-10-20.