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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 isotop
My research is focused on two problems: the long-term evolution of the atmosphere and the long-term evolution of seawater. Emphasis in the first problem area is on the Great Oxidation Event between ca. 2.3 and 2.0 Ga, in particular the change from an atmosphere that probably contained a significant amount of methane to one that contained a significant amount of oxygen. During the next few years we hope to define the cause of this change and to refine its timing.
The past several years have shown that the composition of seawater changed very significantly during the course of the Phanerozoic. However, the actual course of the chemistry of seawater is still poorly defined. The causes are clearly related to tectonism, marine biology, and the flooding of the continents, but a coherent theory relating these processes to the history of seawater remains to be constructed. We hope to contribute materially to this enterprise.