The idea behind the paper (pyroxenite vs. peridotite sources) is intriguing but the paper left myself as well as others in the reading group unconvinced. Figure 2c was particularly problematic; the authors asserted that there data was dissimilar from that of Wang and Eiler 2008, a conclusion I would not draw from looking at the same plot. On a more general note, no matter what the Os or O isotope composition of the sample they were able to explain the result successfully using the Sobolev model. Could they have included other elements (and isotopes) in their model and if so could it still explain the data? It seems to me that there are a lot of knobs to turn to fit this data (a delta 18O of 0 permil for layer 3 crust seems low…) and that without looking at more constraints they can only succeed. Another person took particular umbrage to this, “However, a depleted peridotite source mantle cannot explain the highly radiogenic Os isotope compositions of El Hierro lavas.” Who said that it had to be a depleted source, what about high-temperature metasomatism which they mention in the introduction?