What are banded iron formations and from what period of the

What are banded iron formations, and from what period of the earth\'s history are they associated? What was the likely cause of the changes that resulted in the banded iron formations?

Solution

Banded iron formations are formed from the proterozoic rocks in the earth formed some 1.8 to 2.4 billion years ago. They appear in layers of silica and magnetite in varying thicknesses.

The reason for their formation can be the reaction which we know that occur between oxygen and iron. As there is no free oxygen in the primitive atmosphere of earth, the iron reacted with the O2 formed as a by product of photosynthesis performed the nearby algae on the water surfaces. As the proportion of expanding algae and the available iron becoming inverse, the O2 was left on the sea surfaces and rose to toxic levels. Eventually the algae extincted because of the toxic gases and a silica iron pool got created on the sea surface.

Like this the cycle was continued after algae have been re established resulting these banded iron formations