Certain bacteria which need light are able to eat dissolved iron (Fe2+) and to carry out photosynthesis in the presence of sunlight. But unlike today's green plants, they did not release oxygen in the process. The process produces rust and other iron minerals as waste products. The iron minerals have special qualities -- They absorb harmful ultraviolet radiation, but the part of the sunlight needed for photosynthesis can still be used by organisms. "The iron needed to form the minerals was available in much greater amounts in the oceans than it is today," says Kappler. There are many indications that the photosynthesizing bacteria lived in these early oceans and oxidized iron. "We can still see the results of this today in the form of enormous iron-bearing rocks known as banded iron formations. They are the biggest deposits of iron we have."