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