Before the Siderian period the world had much less oxygen in it. Meaning, seas devoid of oxygen. Durring the Siderian the algae activity that signifies the period began to pump oxygen into the oceans. Allowing then unreactive metalic iron in the sea to be precipitated out into iron oxide. In the case of temperature being a culprit in the Siderian, most likely not. Unless you factor it into giving the agal life energy. Temperature does affect oxidation, but oxidation cannot occur without oxygen. The higher the temperature, the easier it is for oxygen to bond with iron, the lower, the slower it will react.
