Orosirian & Statherian Periods

 Orosirian Period

The 3rd geologic period in the Paleoproterozoic Era is the Orosirian Period, which loosely means ‘mountain range’. This period lasted from 2,050 to 1,800 million years ago.

The latter half of the period involved intense orogeny on virtually all continents. Orogeny is when 2 continental plates slam into each other and one is shoved down, while the other is shoved up, producing mountain ranges.

Other important events include 2 of the largest known impact events. At about 2,023 million years ago, a large asteroid collision created the Vredefort impact structure, located in what is now South Africa. Although most of the crater has eroded away, the impact dome at the center is still visible.

Towards the end of the period, about 1,850 million years ago, the Sudbury Basin was created by the impact of another asteroid in what is now Ontario Canada. I’m not sure if the article was saying the basin is in the city of Greater Sudbury, or the city is in the basin. It did state that the locals merely refer to it as ‘the valley’.

So, the Orosirian Period saw much happening to Earth’s crust, from holes being punched into it (craters) to mountains climbing towards the sky. I couldn’t find anything on life forms or what the environment was like, which is a bummer. I assume the lifeforms that existed at the beginning of this period mostly managed to survive, and possibly evolved.

 

Statherian Period

The final period in the Paleoproterozoic Era is the Stratherian Period, which roughly means ‘stable, firm’. It started at 1,800 million years ago and lasted to 1,600 million years ago.

This period was characterized by erosion and folding. Folding, as I understood the article was when the forces that created mountain ranges continued to deform the land around the mountains, forming foothills. In other places, erosion took place, sending sediment to a lower level, which formed new platforms of land extending out from what land already existed.

The oldest known eukaryotic fossil organism was found in Statherian beds in India, so life was carrying on. At that time, the oxygen level was 10-20% of our current level.

By the beginning of the Statherian Period, the supercontinent Columbia had assembled.

So there we have all the important highlights of the back half of the Paleoproterozoid Era. It almost sound like a livable place. Well, except the oxygen level would be a problem. And I’m not sure we have any earthworms yet to help fertilize the soil. Well, at least we’re getting closer to a livable planet!

 

https://en.wikipedia.org/wiki/Orosirian#:~:text=The%20Orosirian%20Period%20(%20%2F%CB%8C%C9%92r,these%20dates%20are%20defined%20chronometrically.

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

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

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

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

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

Siderian & Rhyacian Periods

 

Siderian Period

There are 4 periods in the Paleoproterozoic Era, the first being the Siderian Period. This period lasted from 2,500 to 2,300 million years ago.

Early in this period is when banded iron formations peaked. As I explained before, cyanobacteria produced waste oxygen, which initially combined with iron that was in the sea, forming magnetite (Fe3O4), an iron oxide, in a crystal structure rock. This process removed iron from the oceans, presumably turning the greenish water clear.

Then, with no remaining iron in the sea to serve as an oxygen sink, the oxygen escaped the ocean and built up the oxygen level in the atmosphere. This led to the oxygen catastrophe, wherein a great deal of the life then existing on the Earth was wiped out because they could not tolerate such high levels of oxygen.

Some geologists believe the high level of oxygen also triggered the Huronian glaciation. This glaciation started in mid-Siderian (2,400 million years ago) and extended into the next period, lasting until 2,100 million years ago. It was apparently caused when free oxygen combined with the methane in the atmosphere to form carbon dioxide and water, which do not retain heat as well as methane does. With far less of this greenhouse gas in the atmosphere, a great chilling took place, also known as the Huronian glaciation. I don’t know if the entire planet froze, and the article stated that this glaciation caused a mass extinction. I’m waiting for a geologist I know to clarify whether there were 2 mass extinctions so close together, or just one, with both the presence of oxygen and the cooling temperatures to blame.

 

Rhyacian Period

The Rhyacian Period is the 2nd geologic period in the Paleoproterozoic era. It lasted from 2,300 to 2,050 million years ago. And that is just about all the wikipedia article had to say on the subject. Oh, there were a bunch of rock formations created, and the Huronian glaciation lasted 100 million years, but that still leaves 150 million years at the end of the period during which, apparently, absolutely nothing of note happened.

Oof! What was the tipping point that caused the end of the glaciation? For that matter, did it cover the entire Earth? Was there an explosion of new species afterwards?

Maybe they don’t know. What about theories? Doesn’t anybody have any theories? Well, without sitting my geologist friend down and picking his brain clean, I guess that’s as far as I can go with this period. Maybe the next 2 period of the Paleoproterozoic Era will have more meat to them.

 

https://en.wikipedia.org/wiki/Siderian#:~:text=The%20Siderian%20Period%20(%20%2Fsa%C9%AA,these%20dates%20are%20defined%20chronometrically.

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

The Paleoproterozoic Era

 Next up is the Paleoproterozoic Era, which spans from 2,500 to 1,600 million years ago. It is the first of 3 sub-divisions (era) of the Proterozoic Eon. It is the longest era of the Earth’s geological history, and is divided into 4 periods, which we will look at later. During this era, the continents first stabilized.

Paleontological evidence suggests that the Earth rotated during this era at a speed that produced days that were 20 hours long, which would have meant a year would have about 450 days long.

It was during this era that the atmosphere and shallow seas saw a great increase in free oxygen, thanks to all that cyanobacteria that had been pumping out oxygen as a waste product for so long. Before that, almost all existing lifeforms were anaerobic, meaning they did not require oxygen. In fact, free oxygen in large amounts is toxic to most anaerobic organism. Therefore, the majority of the anaerobic lifeforms died when the atmospheric free-oxygen levels soared. This was the first major and possibly the most significant mass extinction event, and is called the Great Oxidation Event.

But this was not just a time of death. Many eukaryotes lineages have been approximately dated to the Paleoproterozoic era. Eukaryotes consist of cells that have a nucleus enclosed within a nuclear envelope. To the best that I can remember my high school biology, that would mean that most plants and animals are eukaryotes. It is currently accepted that there are 3 domains of life on Earth, and the eukaryotes are one of them. Bacteria and Archaea are the other two. Neither of these types of life have cells with a nucleus within a nuclear envelope, and I think neither one of them gets large enough to be seen with the naked eye.

During this era, a number of continents collided, creating mountain belts and basins. This happened so often that it led to the assembly of the supercontinent named Columbia (or Nuna, depending on who you talk to).

Now, in doing my research about the Paleoproterozoic Era, I chanced upon a phrase called The Boring Billion. Believe it or not, that sounded interesting, so I did a little more digging (so to speak) and found that it referred to the time period between 1.8 and 0.8 billion years ago, which spans the middle of the Proterozoic eon. It would have just been starting when this era was ending, but I’ll mention it here and hope it comes up again when we get to the next era, so I can study it in more detail.

The Boring Billion section of time was characterized by a fair amount of tectonic stability, climatic stasis, and stalled biological evolution. Supposedly, it was bordered by 2 different oxygenation and glacial events, but the Boring Billion itself had very low oxygen levels and no evidence of glaciation.

Well, no doubt about it, the world is really beginning to shape up into the Earth we know. But I’m not quite ready to move in.

 

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

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

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

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