Osmium (₇₆Os) has seven naturally occurringisotopes, five of which are stable:¹⁸⁷Os,¹⁸⁸Os,¹⁸⁹Os,¹⁹⁰Os, and (most abundant)¹⁹²Os. The other natural isotopes,¹⁸⁴Os, and¹⁸⁶Os, have extremely longhalf-life (1.12×10¹³ years and 2×10¹⁵ years, respectively) and for practical purposes can be considered to be stable as well.¹⁸⁷Os is the daughter of¹⁸⁷Re (half-life 4.12×10¹⁰ years) and is most often measured in an¹⁸⁷Os/¹⁸⁸Os ratio. This ratio, as well as the¹⁸⁷Re/¹⁸⁸Os ratio, have been used extensively in dating terrestrial as well asmeteoricrocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of themantle roots of continentalcratons. However, the most notable application of Os in dating has been in conjunction withiridium, to analyze the layer ofshocked quartz along theCretaceous–Paleogene boundary that marks the extinction of thedinosaurs 66 million years ago. Isotopically pure¹⁹²Os, were it available, would be the densest stable material on earth at 22.80 grams per cubic centimeter.

There are also 31 artificialradioisotopes,^[5] the longest-lived of which is¹⁹⁴Os with a half-life of six years; all others have half-lives under 93 days. There are also ten knownnuclear isomers, the longest-lived of which is^191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive orobservationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.

The isotopic ratio of osmium-187 and osmium-188 (¹⁸⁷Os/¹⁸⁸Os) can be used as a window into geochemical changes throughout the ocean's history.^[6] The average marine¹⁸⁷Os/¹⁸⁸Os ratio in oceans is 1.06.^[6] This value represents a balance of the continental derived riverine inputs of Os with a¹⁸⁷Os/¹⁸⁸Os ratio of ~1.3, and themantle/extraterrestrial inputs with a¹⁸⁷Os/¹⁸⁸Os ratio of ~0.13.^[6] Being a descendant of¹⁸⁷Re,¹⁸⁷Os can beradiogenically formed by beta decay.^[7] This decay has actually pushed the¹⁸⁷Os/¹⁸⁸Os ratio of the Bulk silicate earth (Earth minus thecore) by 33%.^[8] This is what drives the difference in the¹⁸⁷Os/¹⁸⁸Os ratio we see between continental materials and mantle material.Crustal rocks have a much higher level of Re, which slowly degrades into¹⁸⁷Os driving up the ratio.^[7] Within the mantle however, the uneven response of Re and Os results in these mantle, and melted materials being depleted in Re, and do not allow for them to accumulate¹⁸⁷Os like the continental material.^[7] The input of both materials in the marine environment results in the observed¹⁸⁷Os/¹⁸⁸Os of the oceans and has fluctuated greatly over the history of our planet. These changes in the isotopic values of marine Os can be observed in themarine sediment that is deposited, and eventuallylithified in that time period.^[9] This allows for researchers to make estimates on weathering fluxes, identifying flood basalt volcanism, and impact events that may have caused some of our largest mass extinctions. The marine sediment Os isotope record has been used to identify and corroborate the impact of the K-T boundary for example.^[10] The impact of this ~10 km asteroid massively altered the¹⁸⁷Os/¹⁸⁸Os signature of marine sediments at that time. With the average extraterrestrial¹⁸⁷Os/¹⁸⁸Os of ~0.13 and the huge amount of Os this impact contributed (equivalent to 600,000 years of present-day riverine inputs) lowered the global marine¹⁸⁷Os/¹⁸⁸Os value of ~0.45 to ~0.2.^[6]

Os isotope ratios may also be used as a signal of anthropogenic impact.^[11] The same¹⁸⁷Os/¹⁸⁸Os ratios that are common in geological settings may be used to gauge the addition of anthropogenic Os through things likecatalytic converters.^[11] While catalytic converters have been shown to drastically reduce the emission of NO_x and CO, they are introducingplatinum group elements (PGE) such as Os, to the environment.^[11] Other sources of anthropogenic Os include combustion offossil fuels, smeltingchromium ore, and smelting of somesulfide ores. In one study, the effect of automobile exhaust on the marine Os system was evaluated. Automobile exhaust¹⁸⁷Os/¹⁸⁸Os has been recorded to be ~0.2 (similar to extraterrestrial and mantle derived inputs) which is heavily depleted (3, 7). The effect of anthropogenic Os can be seen best by comparing aquatic Os ratios and local sediments or deeper waters. Impacted surface waters tend to have depleted values compared to deep ocean and sediments beyond the limit of what is expected from cosmic inputs.^[11] This increase in effect is thought to be due to the introduction of anthropogenic airborne Os into precipitation.

The long half-life of¹⁸⁴Os with respect to alpha decay to¹⁸⁰W has been proposed as aradiometric dating method for osmium-rich rocks or fordifferentiation of a planetary core.^[2][12][13]

Daughter products other than osmium

• Isotopes of iridium
• Isotopes of rhenium
• Isotopes of tungsten

• Isotope masses from:
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean;Wapstra, Aaldert Hendrik (2003),"The NUBASE evaluation of nuclear and decay properties",Nuclear Physics A,729:3–128,Bibcode:2003NuPhA.729....3A,doi:10.1016/j.nuclphysa.2003.11.001
• Isotopic compositions and standard atomic masses from:
  • de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003)."Atomic weights of the elements. Review 2000 (IUPAC Technical Report)".Pure and Applied Chemistry.75 (6):683–800.doi:10.1351/pac200375060683.
  • Wieser, Michael E. (2006)."Atomic weights of the elements 2005 (IUPAC Technical Report)".Pure and Applied Chemistry.78 (11):2051–2066.doi:10.1351/pac200678112051.
• "News & Notices: Standard Atomic Weights Revised".International Union of Pure and Applied Chemistry. 19 October 2005.
• Half-life, spin, and isomer data selected from the following sources.
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean;Wapstra, Aaldert Hendrik (2003),"The NUBASE evaluation of nuclear and decay properties",Nuclear Physics A,729:3–128,Bibcode:2003NuPhA.729....3A,doi:10.1016/j.nuclphysa.2003.11.001
  • National Nuclear Data Center."NuDat 3.0 database".Brookhaven National Laboratory.

• • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.).CRC Handbook of Chemistry and Physics (85th ed.).Boca Raton, Florida:CRC Press.ISBN 978-0-8493-0485-9.

• Isotopes of osmium
• Osmium
• Lists of isotopes by element

• Articles with short description
• Short description with empty Wikidata description