Mesoarchean & Neoarchean Eras

 Mesoarchean Era

We will continue studying the Archean Eon with a brief look at its 3rd part, the Mesoarchean Era. How brief a look? That will depend on how much I find.

The Mesoarchean Era lasted from 3,200 to 2,800 million years ago. There is no specific level in the rocks that designates this era, it is simply defined by the time period.

Fossils from Australia prove that stromatolites have been growing on Earth since the Mesoarchean Era. These sedimentary formations are created by photosynthetic cyanobacteria that produce adhesive compounds and cement sand and other rocky materials into mineral “microbial mats”. These multi-layered sheets of microorganisms, mainly bacteria, grow at interfaces between different types of material, mostly on submerged or moist surfaces. They have been known to colonize environments ranging in temperature from -40C to 120C (about -48F to 272F). The mats grow layer by layer and can grow to a meter or more. Although uncommon today, fossilized stromotalites record ancient life on Earth. The earliest reefs, probably formed by stromatolites, date from this era.

The article had a tantalizing statement about the Pongola glaciation occurring around 2,900 million years ago but a brief search couldn’t find any more information about it. Was it only at the poles, or was it world-wide?

At the end of this era, the first supercontinent broke up, right about 2,800 million years ago.

 

Neoarchean Era

That brings us to the 4th part of the Archean Eon, the Neoarchean Era,  from 2,800 to 2,500 million years ago. Again, this era is defined only by time, not to a specific rock level.

During this era, oxygenic photosynthesis released an abundance of oxygen, which first reacted with minerals and afterward was free to react with greenhouse gases of the atmosphere. By reacting with these greenhouse gases, the oxygen changed them into gases that trapped less heat in the Earth’s atmosphere, and the Earth began to cool off. Eventually.

Remember the microbial mats from the Mesoarchean Era? Did I mention these mats were created by cyanobacteria? Cyanobacteria give off oxygen as a waste product. We should celebrate the ancient existence of cyanobacteria as the provider of the oxygen that we need in order to live.

However, back then, what life existed could not use oxygen. In fact, it was poisonous to most forms of life of the time. So when O2 levels got too high, a lot of the existing life died off. But that happened later. The process that led to that problem was only beginning during the Neoarchean Era.

Also during the Neoarchean Era, at about 2,720 million years ago, the supercontinent Kenorland formed.

 

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

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

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

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

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