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

Eoarchean & Paleoarchaen Eras

 Eoarchean Era

The Archean Eon is divided into 4 eras, the first of which is the Eoarchean Era. This era began immediately after the Hadean Eon 4 billion years ago, when the Earth had cooled enough to have a solid crust. However, this crust may have been incomplete, with lava flowing at many sites at the surface.

In addition, the beginning of the Eoarchean Era saw heavy bombardment of the inner solar system by asteroids. The oldest rock formations yet discovered occur in Greenland and Canada. The former has been dated to 3.8 billion years old, and the latter 4.031 billion years old.

The Eoarchean Era ended 3.6 billion years ago. The earliest forms of life began within this era. The atmosphere had no oxygen and the atmospheric pressure was from 10 to 100 times what we feel now.

Man, that is a lot of atmosphere. And not a bit to breathe. I mean, you could breathe it, but without any oxygen, breathing wouldn’t do you any good. And the article said life got started at this point, but they didn’t even give that life a name for me to do further research. Well, it was a long time ago, when things on Earth were still pretty... unsettled.

 

Paleoarchaen Era

The next era of the Archean Eon is the Paleoarchaen Era. Not a lot to report on here, either, as this article was even shorter than the one on the Eoarchean Era.

The Paleoarchaen Era started 3.6 billion years ago and ended at 3.2 billion years ago. There are no big happenings at either end to mark the changing of eras, it is simply a convenient way for scientists to refer to this section of the Earth’s history.

The oldest confirmed form of life is fossilized bacteria in microbial mats, approximately 3.480 billion years old and found in Australia.

This is when the first supercontinent formed, and if you remember from my earlier blogs, that would either be Ur or Vaalbara, depending on which one your college professor prefers. There is firm belief that there was one at this time, but there is some debate over the name, and exactly what pieces of crust fit where in it.

Also during this era, a large asteroid, about 23-36 miles wide, collided with the Earth in the area of South Africa. This was approximately 3.26 billion years ago, and created the Barberton greenstone belt.

I can’t help but wonder how that managed to happen. Ur/Vaalbara may have been the supercontinent of the time, but it only held about 12-15% of the continents we currently have. Math says that that ‘supercontinent’ would have covered less than 5% of Earth’s surface. How did a random asteroid just happen to hit that?

I didn’t see anything different regarding the atmosphere, so I’m assuming it was much the same as during the Eoarchean Era. Keep holding your breath. Sooner or later, oxygen starts.

 

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

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

Our Sister Planet

What did you learn about Venus - sometimes called our sister planet - when you were in school? Unless you are still in school, chances are that at least some of those ‘facts’ have changed.

Venus has been called Earth’s twin, because it is similar to Earth in size and mass. Venus’ diameter is 7,520.8 miles, only 396.7 miles smaller than Earth’s. Its mass is 81.5 % of Earth’s. But in other ways, they are not very alike at all.

Venus is still the second planet from the Sun, it is still named after the Roman goddess of love and beauty. It orbits the sun in 224.7 Earth days. A Venus day is 243 Earth days, so its day is longer than its year. It also rotates in the opposite direction as Earth, so on Venus, the sun rises in the west and sets in the east. It still does not have any moons.

Venus has the densest atmosphere of the 4 inner planets, which consists of more than 96% carbon dioxide. At Venus’ surface, the atmospheric pressure is 92 times that of Earth, or roughly the pressure found at 3,000 ft underwater on Earth.

Venus is the hottest planet in the solar system, with a mean surface temperature of 863°F. Mercury is closer to the sun, but Venus is hotter. It is shrouded by an opaque layer of clouds of sulfuric acid. It may have had water oceans at some point in the past, but they would have vaporized due to a runaway greenhouse effect. That water vapor would have photodissociated, and the resulting free hydrogen swept into interplanetary space by the solar wind because Venus doesn’t have a planetary magnetic field. It is postulated that the surface of Venus is a desertscape interspersed with slab-like rocks and is periodically resurfaced by volcanism.

In my youth, I remember reading books and short stories that postulated that Venus weather included perpetual rain, and that Venus was a water planet. In both cases, humans from Earth had colonized Venus. But given the updated information on Venus’ atmosphere and surface, colonization may have to wait until some type of reclamation can happen. Perhaps remove some (a lot!) of carbon from the atmosphere, and set up some type of artificial field around the planet to keep the solar wind from removing any more of the lighter elements from that atmosphere. If we can lessen the green-house effect, then maybe the volcanism will also settle down a bit.

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

Extinction Event 1

We all know the dinosaurs went extinct. Okay, most of them. But that was not the first ‘Great Extinction Event that Earth has suffered. Since I’m really only aware of that one and its possible cause, I decided to investigate the first one, just to see what I could find. Apparently, it was caused by oxygen!

I know, right? Something we think is a good thing, yet it caused a massive die-off! How could this be? Let’s take a look.

First, let’s be sure we understand what an extinction event is; it is a widespread and rapid decrease in the biodiversity on Earth. Estimates of how many extinction events we’ve already had range from 5 to as many as 20.

Most life on Earth is microbial and thus difficult to measure. Therefore recorded extinction events are those that affected the easily observed, biologically-complex component of life on Earth. Normally, extinction of various lifeforms occur at an uneven rate. An Extinction Event is when a lot of different lifeforms go extinct at pretty much the same time.

The Oxygenation Crisis occurred around 2.45 billion years ago, but technically, as I studied it further, it is not considered one of The Great Extinction Events. Maybe because it’s hard to find fossils from that long ago, so they can’t be sure what died off and in what numbers, but it was big enough that the fossils they have found indicate something happened.

From what I understand, Earth’s atmosphere at the time had next to no free oxygen in it. But then photosynthesizing cyanobacteria (which some call blue-green algae) evolved in the shallow sea that covered most of Earth. The cyanobacteria did what it does, and in the process, released free oxygen into the water. Eventually, the water couldn’t hold any more of it and released free oxygen into the air. All this free oxygen (which was a mere pittance compared to what we currently have in our atmosphere) played havoc with the metabolism of most of the living organisms at the time and a great deal of them died.

And the cyanobacteria continued putting out more oxygen.

Which opened the gates for more complex biolife forms.

So, extinction events are not always a bad thing... if you aren’t a species that is going extinct. But they do tend to create ‘bottle-necks’ of survival, which are followed by much evolving and diversification to fill all the empty niches that result.

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