Pictured in 2008, a banded iron formation about 2.5 billion years old near Soudan Underground Mine State Park in Minnesota shows alternating layers of silica-rich (red) and iron-rich (gray) minerals. This type of ancient rock formation dominated the global ocean floors for more than two billion years, but abruptly disappeared 1.7 billion years ago. A study by researchers at UW-Madison and elsewhere describes a new model of how these ancient rocks formed and what they reveal about the geology, oceans and atmosphere of the Earth’s early environment.
Photo: Huifang Xu