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

Hadean Eon

Unless you have a degree in geology or paleontology or something similar, you are probably as confused by the various Ages, Eons and Periods that get named when you look anything up about the History of Earth. I decided to take a look at one of them, and see if I could get it figured out as to when it happened, what major events happened during it... that sort of thing.

So, I had a list of these names, and I picked one at random: the Hadean Eon.

Turns out, I had picked the very first of Earth’s Eons; it started with the formation of Earth about 4.6 billion years ago and ended approximately 4 billion years ago. Other names for it are the Priscoan Period and the Pre-Archean Eon.

Obviously, since we are looking at the very first half billion years of the world, we won’t be talking about dinosaurs or super continents. What could there possibly be to discuss? Well, let’s dig in and see what turns up.

First, there’s the name, which gives us a clue about what was going on. ‘Hadean’ comes from Hades, the Greek god of the underworld. And that describes the conditions of what Earth was going through: The planet had just formed and it was very hot due to a number of factors, including frequent collisions with other Solar System bodies.

One important collision happened about 4.5 billion years ago, when a Mars-sized planetoid smashed into the infant Earth. The collision sent quite a lot of material into orbit around Earth, while the planetoid and the rest of Earth merged and tried to settle down. The orbiting material probably took less than a century to form the moon.

The big collision didn’t melt all of the Earth, but a fair fraction of material was vaporized, which created a rock vapor atmosphere around the young planet. But that rock vapor would have condensed out within 2,000 years, and left behind an atmosphere heavy in CO2 with some hydrogen and water vapor.

Apparently, there was a sizable quantity of water in the material that formed the Earth. After the moon was formed, the surface temperature was about 230C (446F), but even so, oceans of liquid water existed. That’s because the atmospheric pressure was over 27 times what it is today, because of the heavy CO2 atmosphere. As cooling continued, most of the CO2 was removed from the atmosphere by subduction and dissolving in ocean water, but the levels oscillated wildly.

One theory posits that between 4.4 and 4.1 billion years ago, the Earth’s climate was relatively cool, allowing for liquid water to be present at least that long. It was even suggested that the Earth may have been pretty much like it is today, except for the absence of flora and fauna.

One of the articles implied that life may have been getting started by the end of the Hadean Eon. But that was almost like a throw-away at the end of the last paragraph, so I’m thinking , one celled organisms? Maybe?

So as far as stories go, what if a spaceship gets too close to a forming star system and gets clobbered by tiny planetoids until it is forced to crash land on the nearest planet, which just happens to be vaguely Earth-like, but the only life it has are some quasi-amoebas swimming in the oceans. Maybe they have plants or seeds aboard, so they can grow some food. What about the stuff they don’t realize they’re carrying? Cockroaches, mice, fungal spores... What would those things evolve into, once there was enough food on the planet for them to successfully venture off the ship? There would be a whole lot of niches in the food chain for them to fill!

https://en.wikipedia.org/wiki/Giant-impact_hypothesis

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