(Table, page 742) Radium concentration in a manganese nodule found buried in a red clay core from the Central Pacific Ocean

The surprisingly high content of radium in certain deep-sea sediments discovered nearly fifty years ago by J. Joly remained unexplained until 1937, when H. Pettersson suggested an ocean-wide precipitation of ionium from sea water on to the ocean bottom as its origin. Extensive radium measurements on deep-sea cores raised by the Swedish Deep-Sea Expedition carried out in this institute by Pettersson, T. Bernert and me did not confirm the regular vertical distribution of radium reported by other workers. An expected rise in radium content from moderate values in the uppermost surface layers to a maximum corresponding to a radioactive equilibrium between precipitated ionium and ionium-supported radium generally occurred; but the maximum was not followed by the theoretical exponential decline downwards governed by the rate of decay of ionium, to 50 per cent in 83,000 years, to 25 per cent in 166,000 years, etc. Instead, a number of secondary maxima of radium content separated by equally pronounced minima were observed (see graph), which could not well be explained as due to intervening changes in the rate of total sedimentation. Another explanation offered was that ionium and radium are not in radioactive equilibrium; that is, the assumption underlying the use of measurements of radium as indicating the concentration in the same layer of its mother element is unjustified