Archaen Eon

 

The Archean Eon is the second of the four geologic eons of Earth’s history. (The first was Hadean Eon.) During the Archaen Eon, which lasted roughly 4,000 to 2,500 million years ago, the Earth’s crust cooled enough to allow the formation of continents and the beginning of life on Earth. Sounds like a busy time, doesn’t it?

The oldest rock formations on Earth’s surface are Archean. They are found in Greenland, Siberia, Canada, Montana, Wyoming, Scotland, India, Brazil, western Australia and southern Africa, as well as other regions. Volcanic activity was much higher than it is today, producing many different kind of volcanic rocks.

The continents started to form during the Archean, although details are still being debated.  Although this is when the first continents formed, rock of this ages makes up only 7% of the present world’s land mass. Allowing for erosion and destruction of past formations suggests that only 5-40% of the present area of continents formed during the Archean Eon.

By the end of the Archean, plate tectonic activity may have been similar to that of the modern Earth. For those who know how to read it, evidence demonstrates that liquid water was prevalent and deep oceanic basins already existed.

The Archean atmosphere had very little free oxygen, yet temperatures appear to have been near modern levels. The moderate temperatures may be because of greater amounts of greenhouse gases. Or, the Earth may have reflected less sunlight and heat due to having less land area.

There is substantial evidence that life began either near the end of the Hadean Eon or early in the Archean Eon.

The earliest identifiable fossils consist of stromatolites, which are microbial mats formed in shallow water by cyanobacteria. The earliest were found to be 3.48 billion years old. They were found throughout the Archean and became common late in the Eon. Cyanobacteria were instrumental in creating free oxygen in the atmosphere, and created so much of it that later, there was a crisis of sorts, when the life that existed at the time could not cope with the high level of oxygen. (I read that somewhere and have included it in one of my other blogs, but at this time, I can’t remember where I got that from.)

It is generally agreed that before the Archean Eon, life as we know it would have been severely challenged by the hostile environmental conditions then found on Earth.

Life during the Archean consisted of simple single-celled organisms such as Bacteria.

However, fossilized microbes from terrestrial microbial mats show that life was already established on land as long ago as 3.22 billion years.

So, it was a busy time. Lots of water sloshing around, lots of volcanoes creating land masses, and life beginning to get a first grasp on the place. If we wound up crash-landing on a planet like that, could we survive? Could we cultivate cyanobacteria to create more oxygen for us? Doing that to any large extent might strip out some of the greenhouse gases, which could lower the temperature of the planet. Which only goes to show that you have to be careful what you do to make a place your home.

 

https://en.wikipedia.org/wiki/Archean#:~:text=The%20Archean%20Eon%20(%20%2F%C9%91%CB%90r%CB%88,beginning%20of%20life%20on%20Earth.