How Is Iron Formed on Earth?

Interaction and evolution

• Rocks, water and air worked together to form the iron that makes up most of our plant. Air changed over time and so did water as tides and oceanic volcanoes influenced the temperature and shifted microbes that were hard at work creating systems from the minerals and materials they lived in. Minuscule layers deposited one over another for a long time, creating thin lines of different kinds of iron. Rocks were different at the time these deposits were made because rocks and minerals were of a different material as well. In a sense, the rocks evolved from earlier formations to create bands of iron in what is now the surface of the Earth but what was then ocean floor.

Deposits

• Banded iron formations could have formed when hydrothermal fluids, from interactions between seawater and hot oceanic rock deep in the Earth's mantle, mixed with surface water. The mixing caused an oscillating production of minerals rich with iron and silica, which were deposited in layers on the floor of the ocean. Much of this silica is left in the form of sand. Geologists call the time when these iron formations were most prevalent the Archaean-Early Proterozoic and they were dominant between 3.5 and 1.7 billion years ago, but then these bands disappeared from the geologic record. Huifang Xu, a geology professor partly funded by the NASA Astrobiology Institute, hopes to discover the cause of the geologic change, according to a 2009 press release by Jill Sakai of the University of Wisconsin.

Iron and Sea Water

• A popular theory is that geothermal effects and lunar gravitational influences were responsible for the striation effect of iron on Earth's crust. Iron is a metabolic agent for many microorganisms, which may have been responsible for carrying iron and depositing it. On early Earth there was little to no oxygen, so iron could deposit freely in high concentrations in sea water without an interaction with oxygen to degrade the material. After the oceans declined and left areas dry, the iron was left over in shale-like layered formations.

Patterns of Iron in Rock

• Iron in the oceans would have deposited in shifts of heavy layers followed by less heavy layers of material or iron derivatives due to blue green algae near the surface of the water. It is believed that free iron molecules would have bonded with the surface algae in times when the algae was very prevalent, explaining time periods in the layers of iron where the deposits were less. When the algae shifted to being less prevalent in the water, the iron molecules resumed to deposit on the floor in heavier volume.

Pressure

• Ongoing periods of fluctuating ocean waters are believed to be mainly responsible for spreading iron in its different forms from the base material. The iron seed element in paleogeology is thought to have originated in volcanic interiors by a fusion of the elements through extreme heat and pressure, then released through vents as molten material, then distributed across the ocean floor. The main reason for this theory is that iron concentrations are prevalent in the formation of stars despite the absence of liquid water.