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FIGURE 3 Os isotope data tracking the composition of seawater Os over the last 90 My. The upper figure shows the general increase in the ¹⁸⁷Os/¹⁸⁸Os ratio following the steep decline near the Cretaceous-Tertiary boundary (Peucker-Ehrenbrink et al. 1995). The lower figures show high-resolution data for smaller time slices illustrating the ability of Os to record fine-scale variations in inputs into the ocean. Near the K-T boundary (KTB), this includes contributions of mantle Os attributed to eruption of the Deccan flood basalts and extra-terrestrial Os added by the K-T impactor (Ravizza and Peucker-Ehrenbrink 2003). In the Oligocene (lower-left figure), the rapid rise in the¹⁸⁷Os/¹⁸⁸Os ratio is attributed to an increase in continental weathering after removal of glacial cover exposed fine-grained glacial sediments (Dalai et al. 2006).

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