The first red beds
Iron rusts on land for the first time, and Earth's continents turn red.
- When
- Known to
- ± 100 million years
- Era
- Paleoproterozoic, Proterozoic
Continental sediments deposited after about 2.3 billion years ago contain oxidised iron, staining them red — a colour impossible in an oxygen-free world. Their appearance is direct physical evidence that free oxygen had reached the land surface, complementing the isotope evidence from marine rocks. Red beds have been forming ever since.