Like other iron minerals, green rust readily absorbs dissolved elements onto its surface, but green rust is not only particularly efficient at this in many cases, it can also react with toxic dissolved trace metals to make them insoluble, and as a result, renders them in nontoxic forms.
Over millions of years this created an oxygen-rich atmosphere that rapidly removed electrons from minerals near the surface, creating rust out of iron and forming thousands of new minerals from other metals like nickel, copper and uranium.