The igneous rocks of all the Line Islands consist of alkali basalts and hawaiites, and are similar to those found in the Hawaiian Islands. Several models have been proposed to explain the formation of the chain's complex geology. In 1972, the American geophysicist W. Jason Morgan postulated that the chain was formed 70 myr ago in parallel with the creation of the Hawaiian Islands, each by means of a single hotspot. Other experts argued against this model, pointing to geometric and paleomagnetic evidence, and the complex timing of the volcanic episodes that created the Line Island chain. In a 1976 paper, Winterer implied that chains of volcanoes were created by a series of individual hotspots.