Question

The appearance of banded iron layers in the rock record between 1.08 and 3.8 billion years ago reflect the alteration of oxygen-rich and oxygen-poor conditions in the ocean at that time.
True or False

Answer 1

The appearance of banded iron layers in the rock record between 1.08 and 3.8 billion years ago reflect the alteration of oxygen-rich and oxygen-poor conditions in the ocean at that time is True.

Explanation:

Banded rocks have layers of iron oxide and cherts that contain silica. The layer containing iron oxide has a dark color and the chert layer is red in color. Haematite and magnetite are usually the iron oxides that make up the banded rocks.

Banded rocks were formed by the reaction of iron in the oceans with the oxygen produces by photosynthetic bacteria in the ocean. The reaction caused the formation of iron oxides and their precipitation as Banded iron formations.

The presence of free oxygen is crucial for the formation of banded rocks and the formation reduced drastically after 1800 mya period when  atmospheric oxygen availability was reduced.  Banded rocks represent the oxygen rich and oxygen-poor condition of the ocean at that time.