Civilization and the Importance of Iron and Oxygen

Steel is used everywhere in our daily lives, but we are not quite sure where it came from. Even though we know it is extracted from an iron ore, most of us may not know how an iron ore looks like, much less how it has been generated. This time, I am going to introduce one of its places of origin along with earth's history glimpsed by iron ores there.

I don't know how long it took for a train to cut across my way. It may have taken more than 10 minutes. In such a situation, it would be natural for people to be frustrated or get mad, but that wasn't the case with me. I was so much captured by the sight in a car.

I am not talking about a railroad crossing in Japan where trains come and go relentlessly nor that I am a train spotter. There was worth watching the sight.

I was on my way from Port Hedland in Australia toward inland when I had encountered a train carrying iron ores to port. There was no other car except mine. Numerous numbers of wagons were slowly dragged by only one locomotive engine.

The iron ores were extracted from a stratum generated 2.5 billion years ago at an open pit mining in Pilbara area. Iron ore layer can be viewed well from a valley in a national park located near the mine. People can go down the valley, which cuts in an arid plane deeply, to closely view iron ore walls.

The walls exhibit a red brown beautiful stripe pattern of stratum. The stripe is as small as a few millimeters when looked closely, but at the same time, one can see much bigger stripe patterns in distance. Stratum, which contains an iron ore is named banded iron formation after its stripe pattern.

The difference of the amount of iron contained in each layer contributes to form the stripe pattern. A layer containing larger amount of iron becomes an iron ore. Iron ore is the name of a rock, which consists mainly of oxide iron (magnetite, hematite, limonite and others). A layer containing less steel is made of rocks called chert, which mainly consists of quartz.

Hemersley in western Australia is the place where banded iron formation is extended as far as one can see. Open pit mining carried out in a mine there is so vast that it is possible to be pointed out from space. Trucks that carry out iron ore mined massively from the area are also gigantic, whose tires are taller than people.

Large scaled banded iron formation was mostly formed approximately 2.5 billion years ago, and all the iron ore there had been formed no later than 1.9 billion years ago.

What can be said by the fact that most of the banded iron formations occurred coincidentally and stopped all of a sudden? Since a large scaled banded iron formation exists all over the world, it is estimable that some kind of worldwide phenomenon has occurred back in those days.

Banded iron formation is a kind of sedimentary rock. Since sedimentary rock occurs at the bottom of seas, iron ores occur when iron deposits at the sea bottom. Usually, iron is dissolved in seawater in the form of ion, Fe2+. However, if oxidation progresses due to some reasons to make it Fe3+, chemical reaction occurs to make it Fe(OH)3,