Banded Iron Formations
Telling the Story of Earth’s Oxygen
Published in The EarthSphere Blog
Prologue
My last article in the Forgotten Origins series discussed evidence of when Earth’s first free oxygen arrived. But the story of oxygen is nuanced and the path to an oxygenated world, where multi-celled life could survive, was a long one.Geology has helped to unravel the story.
Rocks Tell the Story
One of the great mysteries of Earth’s early development lies in the seemingly late oxygenation of our atmosphere and oceans. Between 2.4 and 2.3 billion years ago, our planet experienced a dramatic rise in the levels of free oxygen. This saturation of the atmosphere and oceans with significant concentrations of oxygen is dubbed “The Great Oxidation Event.” Before then, free oxygen was sparse, and low concentrations of this key ingredient limited the ability of life to evolve into complex multi-cellular organisms. Today almost all life depends on free oxygen for cellular respiration.
Understanding the history of Earth’s oxygen is intimately tied to ancient geological formations called “banded iron formations.” These rocks display beautiful layering, alternating between black and red bands. The importance of this layering derives from how the red bands get their color. The red comes from the…
