Its atoms were forged by nuclear reactions inside massive stars that exploded, seeding our galactic neighborhood with the raw materials for planets over billions of years before the solar system formed.
Although iron is, by weight, the most abundant element in the solid Earth, most lies hidden in the planet’s core, which may be one immense, silicon-tainted iron crystal …. Less than 6 percent of Earth’s crust is iron, but fortunately for the voracious appetite of Industrial Man, the element is plentiful in oxide-rich ore deposits, including banded iron formations.
BIFs, as they’re known to geologists, are enigmatic. All seem to have started out as sediments on ancient seafloors, and by some estimates the oxide mineral accumulated in all known BIFs contains about 20 times as much oxygen as today’s atmosphere does. Yet some of these deposits accumulated long before Earth’s atmosphere became thoroughly oxygenated, so the source of the oxygen stored in these BIFs is baffling.
Then there’s the mysterious banding, in which thin layers of iron-rich minerals such as hematite (Fe2O3) and magnetite (Fe3O4) alternate with silica-rich, iron-poor bands, usually of jasper and chert.
Finally, some of the BIFs are puzzling simply because they’re so big: They stretch for hundreds of kilometers, a distance over which the banding apparently remains intact. So whatever processes created these formations must have acted over broad areas.
Countless details regarding these formations’ origins are hidden because many older BIFs are metamorphic rocks — they’ve been physically warped and chemically cooked deep within the planet, sometimes for millions of years.
“Despite the fact that people have been looking at these formations for a century or more, we still don’t have a really firm handle on where they formed in the oceans, how they formed and what they’re telling us about the composition of the oceans or the atmosphere at that time,” says geobiologist Kurt Konhauser of the University of Alberta in Edmonton, Canada. “These are, surprisingly, still the questions that are out there.”
It is fun to speculate. Perhaps billions of years ago the earth was hit by a shower of iron. Or… perhaps the iron we now find flattened into strips are the remains of an alien civilization that stopped by on Earth temoprarily, set up an outpost, cranked up the oxygen, then left. These cosmic campers may have left some trash behind which evolved into us.