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