Download Linking rock dating with forensics

Analytische Chemie - Analytische Strategien -WS 2016/2017
Linking rock dating with forensics
A lunar rock: the norite 77215 returned by Apollo 17
Source: http://meteorites.wustl.edu/lunar/apollo/nor_77215,240_2035_l.jpg
You might have read that our solar system is 4.566 billion years (Gyr) old; or that the
oldest mineral ever found on Earth is 4.4 Gyr old; or the oldest rock has an age of 3.9
Gyr, while signs of life emerged about 3.7 Gyr ago.
How do we know these ages? They are all based on radioactive decay systems that are
used in geology to date mineral, rocks and geological events.
One widely used radioactive nuclide for dating is 87Rb, which decays to 87Sr with a
half-life of 48 Gyr and is often referred to as the Rb-Sr decay system.
Questions:
1. How can such decay systems be used for dating? Briefly explain the basic
principles using the Rb-Sr system as an example.
a. What is an isochron?
b. Why does the Earth’s curst have more 87Sr than the Earth’s mantle?
Mantle derived rocks can be found e.g., as lavas e.g. at mid ocean
ridges in the deep ocean or oceanic island. Crustal rocks are mainly
present on continents.
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2. You are given a piece of the lunar rock 77215 (norite) returned by the Apollo
17 mission in 1972 from the moon. Minerals were also separated from this
rock (plagioclase and pyroxene  see Carlson et al. 2014, Table 2).
a. Which analyses are necessary to determine a Rb-Sr age of this rock
using the isochron approach?
b. Which analytical techniques/instruments can be used to obtain this
data?
c. What are potential problems, advantages and disadvantages of the
different techniques?
d. How old is 77215?
3. The isotopes 87Sr or 206Pb and 207Pb are produced by radioactive decay and
have been used to date geological processes. Recently, however, they have
also been applied for forensic questions e.g., in combination with O isotopes.
Please choose an example from the attached literature to briefly illustrate the
power of isotopes to support investigators in finding the region of residence of
unidentified victims.
Suggested Reading:
http://www.tulane.edu/~sanelson/eens211/radiometric_dating.htm
https://www.britannica.com/science/dating-geochronology/Rubidium-strontiummethod#ref584929
Carlson RW, Borg LE, Gaffney AM, Boyet M (2014) Rb-Sr, Sm-Nd and Lu-Hf
isotope systematics of the lunar Mg-suite: the age of the lunar crust and its relation to
the time of Moon formation. Philosophical Transactions of the Royal Society of
London A: Mathematical, Physical and Engineering Sciences 372(2024):20130246.
Font L, Jonker G, van Aalderen PA, Schiltmans EF, Davies GR (2015a) Provenancing
of unidentified World War II casualties: Application of strontium and oxygen isotope
analysis in tooth enamel. Science & Justice 55(1):10-17.
Font L, van der Peijl G, van Leuwen C, van Wetten I, Davies GR (2015b)
Identification of the geographical place of origin of an unidentified individual by
multi-isotope analysis. Science & Justice 55(1):34-42.
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