Banded iron formations (BIFs) contain well developed iron-rich thin alternating layers or laminations as seen here.

In the beginning, there was no oxygen, and iron dissolved in the oceans. When photosynthesis got going, oxygen began to accumulate in the atmosphere and oceans. Some of the dissolved iron oxidised – rusted – and precipitated to the sea floor. Sedimentary layers of iron covered the bottom of the oceans making some of the most stunning and colourful geological records.The name comes from the various coloured layers.

A Z shaped diagram is sometimes used to explain the light-dependent reactions that take place during photosynthesis. As banded iron formations take many shapes, ‘Zs’ are not uncommon, and a suitable nod to the mechanisms that produced them.