ory include: Urbanite and pyrite are readily oxidized today, in modern times, but are found unoxidized in sediments from here, chemical building blocks could not have formed in the presence of oxygen and the simplest living organisms have an anaerobic metabolism and would have been killed by oxygen. It also included the origin of the continental crust. Most of the early crust was mafic and the continental developed secondary to that.The Archean era lasted from 3.8 to 2.5 billion years ago. Upon research and findings, Stomatolites (blue-green algae) have been found in carbonate sediment, algal filament fossils were found aged at 3.5 billion years at the North Pole and in western Australia, and spherical bacterial structures were also found in the area of, present day, South Africa. Rocks found from this era are the products of the early differentiation of small protocontinents, which eventually collided with one another forming larger continents. The Proterozoic was known to range from 2.5 to .57 billion years ago. In this era, there were major changes in the Earths crust as full sized continents assembled and plate tectonics begun to operate. At least one great extinction took place during the Precambrian. Evidence is now supportive of possible three extinctions causing explosive changes in this time. These extinctions may have been the predetermining factor in encouraging the diversification of life forms. These also set the stage for the Cambrian explosion (543 to 510 million years ago) following the Vendian (523-543 million years ago). ...
