Banded Iron Formation - Essay Example

Banded Iron Formation Banded iron formation is distinctive units of sedimentary rocks whose age is in the order of the Precambrian. It is estimated that the banded iron formation is included in the list of the oldest rocks formation. (Nik 532) estimates that the rock was formed over 3000 million years ago. A typical banded iron formation consisted of a repeated thin layer and black iron oxide. The iron oxides commonly found in the banded iron formation are hematite and magnetite. Banded layers containing huge amount of iron ores were deposited over three billion years ago.

Some of the areas with surmountable deposits include Pilbara areas of Western Australia and Minnesota regions. The banded iron deposited in these areas are said to have the biggest economic values and hence mining is quite economical, (Kesler, Stephen 443) During the formation of the banded iron, the earth was covered with acidic medium that to a large extent facilitated the formation of the banded iron. In addition, the great oxygenation that took place facilitated the formation of the hard mineral.

This oxygen was fixated by primitive microorganisms that existed during the formation. Photosynthetic bacteria were largely attributed to the formation of banded iron. These bacteria synthesized their food in chemical processes that released oxygen gas. It is important to note that iron is highly reactive with oxygen and hence, it readily formed iron oxide that settled at the bottom of ancient oceans, (Kesler, Stephen 473). This is the most relevant theory that explains the large existence of iron oxide in several iron ores.

Before the formation of the banded iron, oxygen gas did not exist, (Trendall 1). The gas only became existence as result of chemical reactions in the photosynthetic bacteria. Geologists agree that as the cyanobacteria became numerous in the earth, the oxygen emanating from the photosynthesis accumulated in the atmosphere and hence that is the reason why we have the precious oxygen. In the earth’s ocean, dissolved iron combined with oxygen forming insoluble oxides of iron. The iron oxides then precipitated out leading to a formation of a thin coat on the ocean floor.

The thin layer formed into cherts and shale resulting into a complete cover all over the ocean floor. This brought about the stratification of the oceans and hence the ocean waters is "stratified" Over millions of years ago, iron oxide and silica were precipitated repeatedly over a long period. This resulted in the deposition of alternating layers of hematite (which is red), magnetite (which is black) and the chert (which is grey). The chert is basically pure silica while the magnetite composed a huge percentage of pure iron When the banded iron was being formed, the primitive alga was the only form of life on the earth.

The algae formed structures called stromatolites around the calcium metal. Due to excretion of carbon dioxide by the algae, calcium metal reacted with carbon dioxide in presence of the acidic media to form calcium carbonate. I addition, the algae produced oxygen gas that further facilitated life on earth, (Nik 700). Work Cited Kesler, Stephen E. Evolution of Early Earths Atmosphere, Hydrosphere, and Biosphere: Constraints from Ore Deposits. Boulder, Colo.: Geological Society of America, 2006. Print.   Trendall, A. F. Iron-formation, Facts and Problems.

Amsterdam: Elsevier, 1983. Print.   Nik, I. Precambrian Banded Iron-formations Physicochemical Conditions of Formation. Amsterdam: Elsevier Scientific Publ. ;, 1982. Print