Trudy Myers's Blog, page 23
January 22, 2021
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.
January 15, 2021
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.
January 8, 2021
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
January 1, 2021
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!
December 25, 2020
Orosirian & Statherian Periods
Orosirian Period
The 3rd geologic period in the Paleoproterozoic Era is the Orosirian Period, which loosely means ‘mountain range’. This period lasted from 2,050 to 1,800 million years ago.
The latter half of the period involved intense orogeny on virtually all continents. Orogeny is when 2 continental plates slam into each other and one is shoved down, while the other is shoved up, producing mountain ranges.
Other important events include 2 of the largest known impact events. At about 2,023 million years ago, a large asteroid collision created the Vredefort impact structure, located in what is now South Africa. Although most of the crater has eroded away, the impact dome at the center is still visible.
Towards the end of the period, about 1,850 million years ago, the Sudbury Basin was created by the impact of another asteroid in what is now Ontario Canada. I’m not sure if the article was saying the basin is in the city of Greater Sudbury, or the city is in the basin. It did state that the locals merely refer to it as ‘the valley’.
So, the Orosirian Period saw much happening to Earth’s crust, from holes being punched into it (craters) to mountains climbing towards the sky. I couldn’t find anything on life forms or what the environment was like, which is a bummer. I assume the lifeforms that existed at the beginning of this period mostly managed to survive, and possibly evolved.
Statherian Period
The final period in the Paleoproterozoic Era is the Stratherian Period, which roughly means ‘stable, firm’. It started at 1,800 million years ago and lasted to 1,600 million years ago.
This period was characterized by erosion and folding. Folding, as I understood the article was when the forces that created mountain ranges continued to deform the land around the mountains, forming foothills. In other places, erosion took place, sending sediment to a lower level, which formed new platforms of land extending out from what land already existed.
The oldest known eukaryotic fossil organism was found in Statherian beds in India, so life was carrying on. At that time, the oxygen level was 10-20% of our current level.
By the beginning of the Statherian Period, the supercontinentColumbiahad assembled.
So there we have all the important highlights of the back half of the Paleoproterozoid Era. It almost sound like a livable place. Well, except the oxygen level would be a problem. And I’m not sure we have any earthworms yet to help fertilize the soil. Well, at least we’re getting closer to a livable planet!
https://en.wikipedia.org/wiki/Orosiri....
https://en.wikipedia.org/wiki/Vredefo...
https://en.wikipedia.org/wiki/Sudbury...
https://en.wikipedia.org/wiki/Statherian
December 17, 2020
Siderian & Rhyacian Periods
Siderian Period
There are 4 periods in the Paleoproterozoic Era, the first being the Siderian Period. This period lasted from 2,500 to 2,300 million years ago.
Early in this period is when banded iron formations peaked. As I explained before, cyanobacteria produced waste oxygen, which initially combined with iron that was in the sea, forming magnetite (Fe3O4), an iron oxide, in a crystal structure rock. This process removed iron from the oceans, presumably turning the greenish water clear.
Then, with no remaining iron in the sea to serve as an oxygen sink, the oxygen escaped the ocean and built up the oxygen level in the atmosphere. This led to the oxygen catastrophe, wherein a great deal of the life then existing on the Earth was wiped out because they could not tolerate such high levels of oxygen.
Some geologists believe the high level of oxygen also triggered the Huronian glaciation. This glaciation started in mid-Siderian (2,400 million years ago) and extended into the next period, lasting until 2,100 million years ago. It was apparently caused when free oxygen combined with the methane in the atmosphere to form carbon dioxide and water, which do not retain heat as well as methane does. With far less of this greenhouse gas in the atmosphere, a great chilling took place, also known as the Huronian glaciation. I don’t know if the entire planet froze, and the article stated that this glaciation caused a mass extinction. I’m waiting for a geologist I know to clarify whether there were 2 mass extinctions so close together, or just one, with both the presence of oxygen and the cooling temperatures to blame.
Rhyacian Period
The Rhyacian Period is the 2nd geologic period in the Paleoproterozoic era. It lasted from 2,300 to 2,050 million years ago. And that is just about all the wikipedia article had to say on the subject. Oh, there were a bunch of rock formations created, and the Huronian glaciation lasted 100 million years, but that still leaves 150 million years at the end of the period during which, apparently, absolutely nothing of note happened.
Oof! What was the tipping point that caused the end of the glaciation? For that matter, did it cover the entire Earth? Was there an explosion of new species afterwards?
Maybe they don’t know. What about theories? Doesn’t anybody have any theories? Well, without sitting my geologist friend down and picking his brain clean, I guess that’s as far as I can go with this period. Maybe the next 2 period of the Paleoproterozoic Era will have more meat to them.
December 11, 2020
The Paleoproterozoic Era
Next up is the Paleoproterozoic Era, which spans from 2,500 to 1,600 million years ago. It is the first of 3 sub-divisions (era) of the Proterozoic Eon. It is the longest era of the Earth’s geological history, and is divided into 4 periods, which we will look at later. During this era, the continents first stabilized.
Paleontological evidence suggests that the Earth rotated during this era at a speed that produced days that were 20 hours long, which would have meant a year would have about 450 days long.
It was during this era that the atmosphere and shallow seas saw a great increase in free oxygen, thanks to all that cyanobacteria that had been pumping out oxygen as a waste product for so long. Before that, almost all existing lifeforms were anaerobic, meaning they did not require oxygen. In fact, free oxygen in large amounts is toxic to most anaerobic organism. Therefore, the majority of the anaerobic lifeforms died when the atmospheric free-oxygen levels soared. This was the first major and possibly the most significant mass extinction event, and is called the Great Oxidation Event.
But this was not just a time of death. Many eukaryotes lineages have been approximately dated to the Paleoproterozoic era. Eukaryotes consist of cells that have a nucleus enclosed within a nuclear envelope. To the best that I can remember my high school biology, that would mean that most plants and animals are eukaryotes. It is currently accepted that there are 3 domains of life on Earth, and the eukaryotes are one of them. Bacteria and Archaea are the other two. Neither of these types of life have cells with a nucleus within a nuclear envelope, and I think neither one of them gets large enough to be seen with the naked eye.
During this era, a number of continents collided, creating mountain belts and basins. This happened so often that it led to the assembly of the supercontinent named Columbia (or Nuna, depending on who you talk to).
Now, in doing my research about the Paleoproterozoic Era, I chanced upon a phrase called The Boring Billion. Believe it or not, that sounded interesting, so I did a little more digging (so to speak) and found that it referred to the time period between 1.8 and 0.8 billion years ago, which spans the middle of the Proterozoic eon. It would have just been starting when this era was ending, but I’ll mention it here and hope it comes up again when we get to the next era, so I can study it in more detail.
The Boring Billion section of time was characterized by a fair amount of tectonic stability, climatic stasis, and stalled biological evolution. Supposedly, it was bordered by 2 different oxygenation and glacial events, but the Boring Billion itself had very low oxygen levels and no evidence of glaciation.
Well, no doubt about it, the world is really beginning to shape up into the Earth we know. But I’m not quite ready to move in.
https://en.wikipedia.org/wiki/Paleopr...
December 5, 2020
Proterozoic Eon
Now to move on to the next eon, the Proterozoic Eon. This eon spans the time from the appearance of oxygen in Earth’s atmosphere to just before the proliferation of complex life such as trilobites or corals. It started at 2,500 million years ago to 541 million years ago, so very nearly 2 billion years. It is divided into 3 eras; the Paleoproterozoic, the Mesoproterozoic, and the Neoproterozoic. We may or may not take a look at each of these in more detail.
The geologic record of the Proterozoic Eon is more complete than for the Archean Eon, which preceded it. The Proterozoic features rock strata that were laid down in extensive shallow inland seas. Studies of these rocks show that the eon had massive continental accretion, including the first definitive supercontinent cycle, and modern mountain building activity.
There is also evidence of glaciations taking place during the Proterozoic. The first began shortly after the beginning of the Proterozoic, with at least four others near the end of the eon. These may have climaxed with the hypothesized Snowball Earth, an idea I am thoroughly fascinated by.
One of the most important events of this eon was the accumulation of oxygen in the atmosphere. Although oxygen was probably released by photosynthesis during the Archeon Eon, it first combined with sulfur and iron in the oceans. Until roughly 2.3 billion years ago, oxygen was only 1-2% of its current level. It is stated that about 1.9 billion years ago, all the iron in the oceans had all been oxidized.
The Proterozoic Eon was tectonically active. The early part of the eon experienced a period of increasing crustal recycling, which suggests subduction. This is where one piece of crust gets shoved under another piece of crust. The bottom crust is eventually melted, while the upper crust buckles into mountains. The melting crust eventually reformed, making the upper bits of crust thick enough to endure. It is believed that 43% of the modern continental crust was formed in the Proterozoic Eon, 39% during the Archean Eon, and only 18% in the current geological eon.
It is commonly accepted that during the Precambrian SuperEon--of which the Proterozoic Eon is a part--the Earth went through several supercontinent breakup and rebuilding cycles.
The supercontinent Columbia was dominant in the early-mid Proterozoic. The article did not say much about Columbia, so we shall skip ahead to Rodinia (1,000-750 Million years ago) of the late Proterozoic. It was created when a series of continents attached to a central craton called Laurentia, which today forms the core of the North American Continent. During its construction, the mountain building processes created the Grenville orogeny located in Eastern North America, from Labrador down through Mexico. From the map, it looks like the Appalachian Mountains could be part of the mountain range that was formed.
The first advanced single celled (eukaryotes) and multi-cellular life roughly coincides with the start of the accumulation of free oxygen. This may have been due to an increase in the oxidized nitrates, which is what eukaryotes use. But the rise of eukaryotes did not preclude the expansion of cyanobacteria. In fact, stromatolites (microbial mats) reached their greatest abundance and diversity, peaking roughly 1,200 million years ago.
The earliest fossils of something like fungi date to 2,400 million years ago. These organisms lived in the deepest areas of water, and had filamentous structures capable of forming branches.
Wow, sounds like Earth was getting busy, doesn’t it? But I still don’t think we could colonize, not with the crops we grow now. There’s too many forms of other life that our crops count on to help them get the nutrients they need from the soil. Plus, I’m not sure what the climate was like, with such a low amount of free oxygen in the atmosphere. Put me back in my pod and let me sleep another million years or so, and then we’ll see.
November 27, 2020
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/Mesoarc...
https://en.wikipedia.org/wiki/Stromat...
November 13, 2020
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 couldbreathe 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.
