Tonian, Cryogenian, and Ediacaran Periods

Tonian Period

The first section of the Neoproterozoic Era is the Tonian Period. It lasted from 1,000 million years ago to 720 million years ago. The breakup of supercontinent Rodinia began around 900-850 million years ago.

The first large evolutionary radiation of organic microfossils occurred during the Tonian Period. This means a huge increase in diversity caused by a large rate of specialization. None of the examples in this article of evolutionary radiation were from the Tonian period, however, probably since it involved microfossils, which most lay people are not terribly familiar with.

So, Rodinia started breaking up, and microorganisms multiplied and diversified. It still sounds like a pretty barren place to me.

Cryogenian Period

The second geologic period of the Neoproterozoic Era was the Cryogenian Period, lasting from 720 to 635 million years ago. There were 2 ice ages during this period, the Sturtian and Marinoan Glaciations, which are said to be the greatest ice ages known on Earth. There is much debate over whether these glaciations covered the entire planet (Snowball Earth) or a band of open sea survived near the equator (Slushball Earth).

In any case, the Sturtian Glaciation lasted from 720 to 660 million years ago, while the Marinoan Glaciation ended at approximately 635 million years ago, although there was no indication when it began. Whenever it began, it was relatively short-lived when compared to the Sturtian.

Fossils of hard-shelled amoeba first appear during this period, as well as the oldest known fossils of sponges. Debate about how much the glaciation might have impacted biology rages on, with some suggesting that several species began during this period.

Me, I much prefer warmer climes.

Ediacaran Period

The end of the Era is marked by the Ediacaran Period, which lasted from 635 million years ago to 541 million years ago.

Fossils from the Ediacaran are sparse, as not a lot of hard-shelled animals had yet evolved. But there were multicellular organisms with specialized tissues. The most common types resemble segmented worms, fronds, disks, or immobile bags. Although Ediacara biota bear little resemblance to modern lifeforms, more than 100 genera have been described.

During this period, the moon was considerably closer, making the tides stronger and more rapid than they currently are. A day was about 21.9 hours long, meaning there were about 13.1 months per year, and approximately 400 days/year.

Okay, now we're getting somewhere. The place had worms and fronds, or at least lifeforms that looked like them. I was particularly pleased with the information about the days being shorter and the moon being closer. How long do you suppose it would take human colonists to get used to a 22-hour day instead of a 24-hour day?

 

https://en.wikipedia.org/wiki/Tonian#:~:text=The%20Tonian%20(from%20Greek%20%CF%84%CF%8C%CE%BD%CE%BF%CF%82,Mya%20(million%20years%20ago).&text=The%20Tonian%20is%20preceded%20by,and%20followed%20by%20the%20Cryogenian.

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

https://en.wikipedia.org/wiki/Cryogenian#:~:text=The%20Cryogenian%20(%20%2Fkra%C9%AA,and%20followed%20by%20the%20Ediacaran.

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

  

Mercury

 I’m sure we all remember Mercury from our school days. It’s the closest planet to the sun, traveling around our local star once every 88 days. Now, I learned—way back when—that Mercury was tidally locked to the sun, meaning that one side was always facing the sun, while the opposite side was forever dark. But such is not the case. It turns out that Mercury spins completely around roughly every 59 Earth days. But because it is also moving around the sun, a day/night cycle is about 176 days long. So it has long days, and short years.

It is the smallest planet of our system... except for the dwarf planets. It is slightly larger than Earth’s moon at 9,525.1 miles around its equator. By the way, Mercury has no tilt to it, so it has no seasons except whatever small differences might occur because its orbit is elliptical and not round. The gravity at its surface is roughly 3/8 that of Earth. So a person weighing 100 pounds on Earth would weigh about 37.5 pounds on Mercury.

Like all the ‘inner’ planets, Mercury is a rocky planet. It’s surface is quite cratered, much like our moon.

It is only 39 million miles from the sun. If you were standing on Mercury, the sun would look 3 times larger than it does on Earth. It would also feel 7 times hotter. The daylight temperature can climb to 800 degrees Fahrenheit. At night, that temperature would plummet to -290 degrees Fahrenheit. Therefore, it is not likely that life as we know it would be able to exist there.

That is particularly true because of the atmosphere, what there is of it. It consists of oxygen, sodium, hydrogen, helium and potassium. These are atoms that are thrown up by blasts of the solar winds as well as micrometeor strikes.

The article stated quite bluntly that Mercury has no moons. How lonely it must be. I also wonder, what if it does? In that case, it would need to be very small, or it would have been found by now. But what if there were a pea-sized moon zipping around Mercury? And let’s suppose we eventually sent a manned mission there, to land on the dark side (since the light side is so hot) to bring back Mercury samples. How many spacemen would be killed by that moon zipping through their space suit (and maybe them) before they figured out what was happening? Or would punching through their space suit slow it down enough that it would fall to Mercury’s surface, and they might never figure it out?

Well, I’d have to stop and figure out the physics. And I’m not sure where my physics book is anymore.

 

https://solarsystem.nasa.gov/planets/mercury

Neoproterozoic Era

 The next Era is the Neoproterozoic Era, which lasted from 1,000 to 541 million years ago. It is divided into 3 Periods, which we will probably take a closer look at, given the chance.

This article says the most severe glaciation occurred in the middle of this era, when ice sheets reached the equator and formed a ‘snowball earth’. I seem to remember reading somewhere that may not have been a hard freeze at the equator, it may have been slushy in the lowest latitudes.

This severe glaciation may have occurred because of the supercontinent Rodinia, which straddled the equator. It broke up into a number of individual land masses during the first period of this era. Somehow, the low-latitude position of most continent pieces caused the large-scale glacial events. We’ll see if this is explained when we look at the individual periods.

Fossils of the earliest complex multicellular lifeforms have been found dating from the last period of this era. These organisms include the oldest definitive animals in the fossil record.

Originally, the fossil remains of multicellular life such as trilobites and archeocyathid sponges were used to designate the beginning of Cambrian Period. Early in the 20th century, other complex fauna started to be found that pre-dated these fossils, so there were multicellular lifeforms during the Neoproterozoic Era, possibly arising in the last period, after the world-dominating glaciers subsided. Some of these early creatures may or may not be ancestors of modern animals. Even the scientists don’t agree on that or on which ancient lifeform may have produced which modern animal.

Another milestone attributed to this era is that this is when the most continental crust was formed.

Well, I managed to boil that entire article down to less than 300 words. I could have included more, but it would have come out sounding more like a thesis, rather than a blog.

Here’s what I look forward to finding out in looking up the 3 periods for the era:

* Anything that happened in the first period, because this article seemed to have glossed right over those years.

* How Rodinia’s ‘children’ all sitting near the equator created such massive glaciers when Robinia itself, sitting on the equator, did not.

* What finally caused the glaciers to retreat? I’ve heard it might have been volcanoes in Siberia (which wasn’t sitting anywhere near where it is today).

* More information about these lifeforms and their supposed modern descendents.

 

https://en.wikipedia.org/wiki/Neoproterozoic#:~:text=The%20Neoproterozoic%20Era%20is%20the,%2C%20Cryogenian%2C%20and%20Ediacaran%20Periods.

Calymmian, Ectasian & Stenian Periods

 

Calymmian Period

There are 3 periods in the Mesoproterozoic Era. However, the article on the first of these periods, the Calymmian Period, was less than 100 words long. The Calymmian Period lasted from 1600 to 1400 million years ago. During this time, the continents expanded by adding sedimentary flatlands. Right in the middle of the period, the supercontinent Columbia started to break up.

 

Ectasian Period

The 2nd period is the Ectasian Period, which in Greek means “extension”. It lasted from 1400 to 1200 million years ago. The name refers to the continued expansion of sedimentary flatlands.

Fossils have been found dating from this period that provide the first evidence of sexual reproduction. This allowed and was necessary for complex multicellularity, in which certain cells of the organism are specialized to perform different functions.

 

Stenian Period

The Stenian Period is the final segment of the Mesoproterozoic Era, lasting from 1200 to 1000 million years ago. The supercontinent Rodinia assembled during the Stenian.

And the Keweenawan Rift formed at about 1100 million years. This rift (tear) occurred in the middle of the North American continent. I had never heard of this rift before. One wonders if North American was much skinnier before the rift occurred and the rift has been filled in since then. If that were the case, the rift could have been as small as the Mississippi River valley, or it could have stretched from the Rocky Mountain foothills to the Appalachian foothills, if those existed at that time. What would have happened if the rift had grown and deepened. Would we have 2 continents where we only have 1?

A closer look at the map provided showed it to be a lop-sided horse-shoe-shaped rift. The 2 ‘arms’ meet at Lake Superior, which defines the northern arc of the rift. The eastern arm trends south into lower Michigan, and possibly as far south as Alabama. The western arm runs southwest into Kansas and possibly as far as Oklahoma. A northern arm, which was not shown on the map, ran up into Ontario and formed another lake, but didn’t go any further.

So, let’s see, if that 3-armed rift had actually grown and spread, we might have had 3 continents where we now only have 1. That would certainly change things up. Now I have alternate histories running rampant through my mind. What do you think about that? Eastern North America, Western North America and a Mexico that reaches Lake Superior.

 

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

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

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

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

Mesoproterozoic Era

The Mesoproterozoic Era is still part of the Proterozoic Eon. It lasted from 1,600 to 1,000 million years ago. This is the first period of Earth’s history which has a fairly definitive geological record. The continental masses of this era were more or less the same ones that exist today, but not necessarily in the same forms.

During this era, the Columbia supercontinent broke up, the Rodinia supercontinent formed, and, oh yeah, sexual reproduction evolved, which greatly increased the complexity of life to come.

Further development of continental plates and plate tectonics took place. This era saw the first large-scale mountain building episode, the Grenville Orogeny. From the maps I’ve see of this mountain range, it could be what produced the Appalachian Mountains and the Ozark Mountains, but it continued down along what is now the Texas Gulf Coast and into northeastern Mexico.

This was the high point of the Stromatolites before they started to decline. Stromatolites are a type of sedimentary rocks created by photosynthetic cyanobacteria when they exuded adhesives, gluing sand and dirt into mats, which eventually bonded together to form rock formations.

During this era, the chemistry of the sea changed, as did the sediments of the earth and the composition of the air. Oxygen levels continued to rise.

I believe this Era has 3 subdivisions, which I will probably study further, just to try to get a sense of what happened when. The problem with using Wikipedia is that the different articles are or can be written by different people, and then don’t always agree. For instance, is this the 2nd time the Grenville Orogeny is said to have happened? I seem to remember it having been mentioned before, because I remember looking at the map of how far it extended.

Another example is that this article said atmospheric oxygen was at 1% of today’s level at the beginning of this era, while another article said it reached 1-2% of today’s levels during a previous period. I suppose that’s not a huge difference, but it does tend to confuse people who are looking for absolute answers. It’s why I only stated that the oxygen levels continued to rise.

Still not ready for colonization, but we’re getting closer!

 

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