I am gobsmacked. By your comments you haven&#x27;t read or know much about the topic, yet you insist that your personal beliefs trump the published work of scores of papers on the topic. But there&#x27;s no reason to go to those papers when The New Yorker piece addresses your concerns:<p>&gt; The ancient iron formations share many characteristics with modern limestones, which suggests that they accumulated in a marine environment. In today’s oceans, iron is in such short supply that it is a limiting nutrient—an essential element whose scarcity holds biological productivity in check. (A controversial climate-engineering scheme is even based on this fact; the idea is that if the oceans were fertilized with iron powder, plankton would bloom enthusiastically and then die, sinking to the ocean floor and sequestering large amounts of carbon there without, fingers crossed, wreaking havoc on the rest of the marine biosphere.) The primordial oceans, by contrast, must have been awash with iron. The richness of the rock formations—imagine all the steel in cars, cutlery, airplanes, buildings, bridges, and railroads—attests to that.<p>Thus when you write &#x27;Fe is used in living things, but only rarely&#x27;, the interpretation should be &#x27;iron is so important to living systems that a biosystem will use all of the biologically available iron. There is so little iron available that it&#x27;s a limiting factor to the ecosystem.&#x27;<p>With the plankton bloom being an example of 1) how iron is a limiting factor, and 2) a process by which iron is removed from the biosphere.