The banded iron formations exposed in this sedimentary rock, originated more than 2..., 2000 (photo)

The banded iron formations exposed in this sedimentary rock, originated more than 2.5 billion years ago as iron-rich seas absorbed the planet's first oxygen. Having perfected photosynthesis cyanobacteria flourished and produced vast amounts of oxygen. Oxygen combined with ferrous oxides and formed crystalized ferricoxide which rained down as sediment on the floor of the Hamersley Basin,which lay as an in land sea. Over millions of years, these iron-rich deposits were transformed bythe pressure of further sediments laid down over them, forcing trapped water to be driven out and gradually turning the sediments into tough, well-bedded rock, more than 2.5 km thick. Horizontal compression later caused rocks to buckle, developingnumerous vertical cracks, before lifting to the surface to form dry land.A sharp drop in the sea-level caused the rivers to cut rapidly through the land, creating sheer-sied gorges; this accompanied by millions of yearsof erosion has sculpted therocks into the present landscape. Photo by Cary Sol Wolinsky