The banded iron formations end
Two billion years of iron layers stop, because the oceans finally run out of dissolved iron.
- When
- Known to
- ± 30 million years
- Era
- Paleoproterozoic, Proterozoic
After a final great pulse around 1.88 billion years ago, banded iron formations largely cease. The oceans had held enormous quantities of dissolved ferrous iron, which oxygen precipitated out layer by layer; once that reservoir was exhausted, the process ended. Their disappearance is one of the clearest signals that ocean chemistry had been permanently transformed. Almost all iron ore mined today comes from rocks older than this line.