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Radioactive, radiogenic and isotope measurements in Earth materials provide useful approaches to the study of terrestrial and cosmic processes. Our laboratory has used these tools to address problems as diverse as the circulation of Long Island Sound and the cosmic dust flux to our planet. A few of the projects are listed:
1. Air samples and atmospheric precipitation are analyzed for 222Rn(radon) daughters such as 210Pb and 214Pb as well as cosmogenically produced 7Be and 35S to determine: (a) the residence times of aerosols in different layers of the troposphere via 214Pb, 210Pb and 7Be, (b) the sources of ozone found in the troposphere based on correlations with 7Be and 210Pb, and (c) the oxidation and precipitation kinetics (including dry deposition) of SO
2. The radioactive decay of 187Re (half-life ca. 4.6x1010 years) produces 187Os. The ratio of 187Os to non-radiogenic Os (nominally represented by 186Os) in rocks undergoing weathering is determined by the Re/Os of the rock and its age. The variation in the relative sources of weathered material (high 187Os/186Os from continental crust, low 187Os/186Os from mantle-derived rocks) is sensed by contemporary sea water osmium and ultimately recorded in accumulating marine sediments. The tectonic history of the past 100 million years is inferred from Os isotope measurements in deep-sea deposits.
3. The measurement of 222Rn(3.4 d), 226Ra(1620 y), 228Ra(5.7 y) and 224Ra(3.6 d) in Long Island Sound water profiles provides information on the mean residence time of water in the Sound as well as the flux of nutrient-rich water from the New York City area. The radium isotopes also indicate the horizontal mixing rates in the Sound.
4. The 222Rn and radium isotopes measured in groundwaters also indicate the retardation factors affecting the movement of cations, some of interest in nuclear waste disposal studies.
5. The cosmic dust flux to Earth is determined from the Os flux of the unique 187Os/186Os. Comparison with another cosmic dust tracer, 3He, provides information on the transport of different size components of the dust through the atmosphere and the oceans before reaching the ocean floor.
6. 87Sr/86Sr of sea water and streams have been shown by others to be a way of translating this ratio into the salinity of coastal waters. Applications to environments of the Mesozoic provide the possibility of working out the life habitats of ancient coastal organisms.
7. Planetary degassing as seen through the study of radiogenic 40Ar provides clues to the rates of recycling of carbon and water through the mantle. These evaluations depend on understanding the composition of the crust and direct measurements of 40Ar flux from the solid earth to the atmosphere.
8. Oxygen isotope signatures preserved in seawater phosphate and phosphatic deposits such as fish debris provide information on the sites of enzymatic equilibration in the water column, and consequently paleothermometry of ancient marine fish habitats.