Investigations of the Isua supracrustal rocks in West Greenland allow us to identify the protoliths and alteration history for most Isua rocks. The protoliths consisted of alternating basalt and banded iron formation. This sequence was invaded by dunitic sills, metamorphosed, and later intruded by felsic gneisses. Pervasive carbonation and K metasomatism produced a sequence of lithologies, mimicking those found in modern platform deposits. However, the protoliths could have originated in a purely oceanic environment with no sialic detrital components. The Isua sequence probably consists of several tectonic panels, some of which are cut by >3810 Ma felsic intrusive rocks.