U–Pb zircon dating

U–Pb zircon dating is a technique used in geology that characterizes the age distributions of zircon crystals in a rock by there age of formation as determined by the ratio of uranium to lead. Zircons are useful for this as they are fairly tough, and can survive weathering from igneous rocks, and transport into sedimentary rocks. Thus the range of ages can be used to indicate the source of material for a sediment.

The process was first used by George Tilton[1]

The process of dating the zircon involves collecting rock samples, grinding them up, separating out the zircons by letting them sink in a dense liquid that floats off most of the other common minerals. Then magnets are used to separate the zircons. Individual zircons are then thinly sliced and placed on a glass plate and examined with a light microscope. Elements are determined by an electron microprobe. The electrons trigger x-rays. Each element has a different pattern of x-ray emission. The crystal can be dissolved in hydrofluoric acid and then examined by mass spectroscopy to determine isotopes.[2]

U–Pb zircon dating was used to show that zircons from Jack Hills crystallized 4.40 billion years ago.[3]

References

  1. ↑ Basu, A., and S. Hart (1996). "Earth Processes: Reading the Isotopic Code". Geophysical Monograph Series (Washington, D. C: AGU) 95: 437.
  2. ↑ Mathez, Edmond A. (2000). "Zircon Chronology: Dating the Oldest Material on Earth". Earth Inside and Out. Retrieved 9 January 2015.
  3. ↑ Wilde, Simon A.; John W. Valley; William H. Peck; Colin M. Graham (2001). "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago". Nature 409 (6817): 175–178. doi:10.1038/35051550. ISSN 0028-0836. PMID 11196637.