Abstract

Over 2 billion years ago banded iron formations (BIF) developed as a consequence of aqueous iron (FeII) precipitating due, in part, to the new presence of oxygen in the Archaen ocean. The outstanding question is how long did it take for the precipitates to rain out of the ocean column, setting onto the ocean floor to form BIF ? We examine an idealisation of this circumstance by performing laboratory experiments in which a solution of ferrous chloride (FeCl2) is combined with a solution of sodium hydroxide (NaOH). If the limiting concentration of one of these two solutions is small, tiny precipitates of “rust” (Fe(OH)3) form, which slowly settle. At larger concentrations, however, the precipitates accumulate into progressively larger flocs that initially settle rapidly, but then form convective flow patterns. Understanding these dynamics is a work in progress.