This is the oldest object we have (3.8 billion years). What does this mean? Actaully, all matter on earth is equally old. It means that it remained relatively unchanged over a period of 3.8 billion years. The matter of , for instance , our bodies is equally old, but it has been through a lot of changes. This is a piece of rock from the Isua Greenstone Belt of Greenland. It is sediment formed 3.8 billion years at the bottom of the sea. We call this a banded iron formation or BIF. Since its formation the sediment turned into sedimentary rock.
Banded Iron Formations (BIFs) consist of alternating layers of iron-rich and silica-rich layers. Here the black layers consist mainly of magnetite. This is a magnetic mineral with chemical formula Fe3O4. The chemical IUPAC name is iron (II, III) oxide and the common chemical name is ferrous-ferric oxide. This magnetite was not sedimented as such at the time because there was no oxygen yet in the air or in the sea. The original sediment contained probably iron silicates that later on was oxidized, when oxygen had become available. The white layers consist of chert.
This stone is a datum. What information do we get out of this? That is a diffucult question which scholars are still far from agreeing. Except from the fact that the circumstances made sedimentation possible, then a new appearance.
But where did the aforementioned oxygen come from??