Abstract
During their formation, marine manganese (or more properly ferromanganese oxide) nodules include and commonly concentrate elements dissolved in seawater. This attribute makes them especially valuable recorders of the isotopic composition of elements supplied to the oceans having radiogenic isotopes, for these can be used in exploring crustal composition and evolution1–5. From measurements of 187Os/186Os ratios in marine manganese nodules and comparison with the 143Nd/144Nd ratios of the same nodules, we have calculated the Os isotopic composition and the osmium and rhenium concentrations of the weatherable portion of the continental crust, together with the proportions of ‘ultra-mafic’ and ‘granitic’ rock that constitute this crustal mass.
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