Tanzanite (sorosilicate)
Around 2.4 billion years ago, the Great Oxygenation Event (GOE) altered the air surrounding Earth from a primordial methane-rich atmosphere into the oxygen-rich one we breathe today. The driving force behind this change was cyanobacteria, single-celled life with the ability to photosynthesize. These microscopic creatures took in carbon dioxide and gave out oxygen.
The oxygen that life produced before the GOE was combining with iron in the rocks rather than building up- in the atmosphere. Then, around 2.4 billion years ago, no more unoxidized iron was left in Earth’s crust. The result—a runaway buildup of oxygen in the atmosphere—changed our planet forever. The gas was then free to combine with existing minerals, and the result was a tripling of mineral types, such as tanzanite (shown above) and others.
500 Cool Astronomy Things 