Thousands of oceanic basalts have been analyzed in the last six decades, building up a large database of Sr, Nd, Hf, and Pb isotope ratios. A characteristic feature of these data is that they are not randomly distributed. In 2D and 3D isotope ratio diagrams, the isotopic variation of oceanic basalts on a local scale, that is, for basalts from one ocean island or ridge segment, is often in form of approximately linear data trends. Combining the local data into a large global data set does not have a randomizing effect. Rather, despite considerable overlap, higher-order structures, that is, reproducible trends or clusters composed of groups of local data, appear in 2-3D isotopic space. These higher-order trends or clusters of the global data set have often been described as linear combinations