Rhenium-Osmium Systematics
Measuring the trillionths?
Shaumik Daityari / @ds_mik
http://sdaityari.github.io/rhenium.osmium.systematics
Rhenium
- Symbol "Re"
- Atomic number 75
- Heavy (specific gravity - 21.02)
- Silvery-White
- Alloys used in filaments of instruments, catalysts in chemical and petroleum industries
- Average concentration of 1 ppb
- Oxidation states from -1 to +7
- Two stable isotopes (185, 187)
- One mineral - Rheniite
Rheniite, Source: Wikipedia
Osmium
- Symbol "Os"
- Atomic number 76
- Hard, Brittle
- Heavy (specific gravity - 22.59)
- Bluish-White
- Alloys are highly durable and extremely hard
- Fountain pen tips and electrical contacts
- Oxidation states from -2 to +8
- Seven naturally occurring isotopes(184, 186, 187, 188, 189, 190, 192)
Source: 
The Rhenium-Osmium Clock
- 187Rhenium is slightly radioactive
- 187Rhenium converts into 187Osmium when a neutron decays to a proton (β decay)
- Half life - 42.3 billion years (~ 10 x age of Earth)
- Osmium is compatible (no preference in absence of iron)
- Rhenium is highly incompatible
- Any rock that undergoes melting in the mantle stops its Re-Os clock
The Rhenium Osmium systematics
Applications
Extraterrestrial Occurrence (1) - Crater size
- Meteorites add osmium to the sedimentary record
- Meteorite osmium hasn't gone through 4 billion years of mantle evolution
- Larger pulses of osmium in the record of seafloor sediments point to asteroid impacts
- Could be used to find out how big the crater was
- Francois Paquay, 2009
- Challenge - determine what fraction vaporized and what fraction dissolved in seawater
- Within 50% variation of known impact sizes
Source: Paquay, 2007
Extraterrestrial Occurrence (2) - Age of meteorite cores
- Meteorite cores contain iron
- Re and Os are siderophiles
- Age of the meteorite core can be determined
- J. J. Shen (1996)
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References
- Dąbek, Józef, and Stanislaw Halas. "PHYSICAL FOUNDATIONS OF RHENIUM-OSMIUM METHOD–A REVIEW." Geochronometria 27.1 (2007): 23-26.
- Paquay, François S., et al. "Absence of geochemical evidence for an impact event at the Bølling–Allerød/Younger Dryas transition." Proceedings of the National Academy of Sciences 106.51 (2009): 21505-21510.
- Selby, David, et al. "Absolute timing of sulfide and gold mineralization: A comparison of Re-Os molybdenite and Ar-Ar mica methods from the Tintina Gold Belt, Alaska." Geology 30.9 (2002): 791-794.
- Shen, J. J., D. A. Papanastassiou, and G. J. Wasserburg. "Precise Re Os determinations and systematics of iron meteorites." Geochimica et Cosmochimica Acta 60.15 (1996): 2887-2900.
- Walczyk, Thomas, Erhard H. Hebeda, and Klaus G. Heumann. "Osmium isotope ratio measurements by negative thermal ionization mass spectrometry (NTI-MS)." Fresenius' journal of analytical chemistry 341.9 (1991): 537-541.
THE END
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