Banded Iron Formation (BIF): How These Rocks Got Their Stripes
Long ago, oxygen filled the oceans. It mixed with iron which reacted by rusting. The seafloor collected rusted iron called banded iron formation (BIF).
Milestone
Great Oxygenation Event: How Oxygen Filled the Atmosphere
Over 4 billion years ago, Earth’s atmosphere was mostly methane & nitrogen. The Great Oxygenation Event marks a time when free oxygen filled the atmosphere.