|
As photosynthesizing organisms pumped oxygen into Earth's atmosphere and ocean, the oxygen reacted with dissolved iron in the oceans and formed massive rock deposits called “banded iron formations.” Once the dissolved iron was used in chemical reactions, oxygen began to increase in the atmosphere. Much of the iron used in industry today originated at this time. Photograph of a banded iron formation outcrop located on the Upper Peninsula, Michigan. The lens cap gives an idea of scale. Image courtesy of Sarah Hanson, Earth Science Department, Adrian College, Adrian, Michigan. |