Banded Iron Formations and evolution of the atmosphere The time between the formation of the earth and the beginning of the Cambrian(about 570mya) is a 4000 my long period known as the Precambrian, this includes approximately 90% of geological time of which we know very little about as pre-Cambrian rocks are poorly exposed, many have been eroded or metamorphosed and fossils are seldom found. The Precambrian has been divided into 3 Eons: 1.Hadean (4600-3800 mya of which …showed first 75 words of 1305 total…

…showed last 75 words of 1305 total…The origin sequence and connection of these events are the issues that are currently in debate. Most are in agreement that they are all linked and that O2 levels are a key factor in the formation of banded iron formation, the problems arise when trying to distinguish when and how O2 began to be produced, the question arises, which came first the oxygen producing bacteria or the oxygen causing life sensitive to it to adapt?