Banded Iron Formations
<p>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 “<em>The Great Oxidation Event</em>.” 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.</p>
<p>Understanding the history of Earth’s oxygen is intimately tied to ancient geological formations called “<a href="https://www.amnh.org/exhibitions/permanent/planet-earth/how-has-the-earth-evolved/banded-iron-formation" rel="noopener ugc nofollow" target="_blank"><em>banded iron formations</em></a>.” 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 inclusion of tiny iron oxide particles in the original sedimentary matrix.</p>
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