Iron returns to the oceans
Sealed under ice, the sea goes anoxic again and banded iron formations reappear after a billion years.
- When
- Known to
- ± 30 million years
- Era
- Neoproterozoic, Proterozoic
With the oceans capped by ice and cut off from the atmosphere, dissolved iron accumulates once more, and banded iron formations are deposited for the first time since 1.85 billion years ago. They stop again as soon as the ice melts and oxygen returns. It is a brief, sharp reversal to Archean-style ocean chemistry, and a strong independent line of evidence for near-total ice cover.