Proterozoic Eon

 Now to move on to the next eon, the Proterozoic Eon. This eon spans the time from the appearance of oxygen in Earth’s atmosphere to just before the proliferation of complex life such as trilobites or corals. It started at 2,500 million years ago to 541 million years ago, so very nearly 2 billion years. It is divided into 3 eras; the Paleoproterozoic, the Mesoproterozoic, and the Neoproterozoic. We may or may not take a look at each of these in more detail.

The geologic record of the Proterozoic Eon is more complete than for the Archean Eon, which preceded it. The Proterozoic features rock strata that were laid down in extensive shallow inland seas. Studies of these rocks show that the eon had massive continental accretion, including the first definitive supercontinent cycle, and modern mountain building activity.

There is also evidence of glaciations taking place during the Proterozoic. The first began shortly after the beginning of the Proterozoic, with at least four others near the end of the eon. These may have climaxed with the hypothesized Snowball Earth, an idea I am thoroughly fascinated by.

One of the most important events of this eon was the accumulation of oxygen in the atmosphere. Although oxygen was probably released by photosynthesis during the Archeon Eon, it first combined with sulfur and iron in the oceans. Until roughly 2.3 billion years ago, oxygen was only 1-2% of its current level. It is stated that about 1.9 billion years ago, all the iron in the oceans had all been oxidized.

The Proterozoic Eon was tectonically active. The early part of the eon experienced a period of increasing crustal recycling, which suggests subduction. This is where one piece of crust gets shoved under another piece of crust. The bottom crust is eventually melted, while the upper crust buckles into mountains. The melting crust eventually reformed, making the upper bits of crust thick enough to endure. It is believed that 43% of the modern continental crust was formed in the Proterozoic Eon, 39% during the Archean Eon, and only 18% in the current geological eon.

It is commonly accepted that during the Precambrian SuperEon--of which the Proterozoic Eon is a part--the Earth went through several supercontinent breakup and rebuilding cycles.

The supercontinent Columbia was dominant in the early-mid Proterozoic. The article did not say much about Columbia, so we shall skip ahead to Rodinia (1,000-750 Million years ago) of the late Proterozoic. It was created when a series of continents attached to a central craton called Laurentia, which today forms the core of the North American Continent. During its construction, the mountain building processes created the Grenville orogeny located in Eastern North America, from Labrador down through Mexico. From the map, it looks like the Appalachian Mountains could be part of the mountain range that was formed.

The first advanced single celled (eukaryotes) and multi-cellular life roughly coincides with the start of the accumulation of free oxygen. This may have been due to an increase in the oxidized nitrates, which is what eukaryotes use. But the rise of eukaryotes did not preclude the expansion of cyanobacteria. In fact, stromatolites (microbial mats) reached their greatest abundance and diversity, peaking roughly 1,200 million years ago.

The earliest fossils of something like fungi date to 2,400 million years ago. These organisms lived in the deepest areas of water, and had filamentous structures capable of forming branches.

Wow, sounds like Earth was getting busy, doesn’t it? But I still don’t think we could colonize, not with the crops we grow now. There’s too many forms of other life that our crops count on to help them get the nutrients they need from the soil. Plus, I’m not sure what the climate was like, with such a low amount of free oxygen in the atmosphere. Put me back in my pod and let me sleep another million years or so, and then we’ll see.

 

https://en.wikipedia.org/wiki/Proterozoic