Planetary Environment and The Oxygen Catastrophe
Evidence illuminating the details of plate motions and other tectonic functions in the Precambrian has been poorly preserved. It is generally believed that small proto-continents existed prior to 3000 Ma, and that most of the Earth's landmasses collected into a single supercontinent around 1000 Ma. The supercontinent, known as Rodinia, broke up around 600 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch, roughly 2200 Ma. The best studied is the Sturtian-Varangian glaciation, around 600 Ma, which may have brought glacial conditions all the way to the equator, resulting in a "Snowball Earth".
The atmosphere of the early Earth is not well understood. Most geologists believe it was comprised primarily of nitrogen, carbon dioxide, and other relatively inert gases, lacking in free oxygen. This has been disputed with evidence in support of an oxygen-rich atmosphere since the early Archean.
Molecular oxygen was not present as a significant fraction of Earth's atmosphere until after photosynthetic life forms evolved and began to produce it in large quantities as a byproduct of their metabolism. This radical shift from an inert to an oxidizing atmosphere caused an ecological crisis sometimes called the oxygen catastrophe. At first, oxygen would quickly combine with other elements in Earth's crust, primarily iron, as it was produced. After the supply of oxidizable surfaces ran out, oxygen began to accumulate in the atmosphere, and the modern high-oxygen atmosphere developed. Evidence for this lies in older rocks that contain massive banded iron formations, laid down as iron and oxygen first combined.
Read more about this topic: Precambrian
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