The banded iron ores of the Hamersley Gorge in Karijini National Park of northwestern Australia date back to the archaic epoch of our planet. About 2500 million years ago, these layered banded iron sediments were deposited at the bottom of a shallow sea. Bacteria played a decisive role in this process. They had the ability to oxidize the iron dissolved in seawater, causing it to sink to the sea floor as rusty mud.