#paleoproterozoic

[katborg82]

I'm gonna try and rush through these next few eras as we're covering a lot of time with not much excitement.

The Paleoproterozoic era started off the Proterozoic eon about 2.5 billion years ago. With the microbial cyanobacteria thriving and photosynthesizing, the world would face some major consequences. The drastic increase of oxygen in the atmosphere would cause the Great Oxidation Event, which would kill off a huge majority of the microbial ecosystem populating Earth. The first mass extinction.

This event also sent earth into a series of ice ages over the next 300 million years. This was known as the Huronian Glaciation. It's a miracle that life pushed through this snowball Earth, but it wouldn't be long before it happened again..

[soaringornithopter]

"Genesis", Oil on canvas by Matthew Cornell

[good-night-space-kid]

Geology and The Terror

As a geologist who is incapable of turning off their geology brain even while watching shows for fun, one of the things that baffles me a bit about The Terror is why they continuously refer to the landscape as shale when both King William Island and the filming location in Pag, Croatia are dominated by limestone. Given the desolation of the landscape, the geology is rather at the forefront of many scenes so it was fun to try and parse it out as I watched.

King William Island, Nunavut, Canada

According to the official map of the bedrock of the region as published by the Canadian government (Harrison et al., 2015), the entirety of King William Island is mapped as dolostone, dolomitic limestone, and limestone with only minor components of shale, sandstone, conglomerate, and breccia. This is a shelf marine deposit dating back to the Late Cambrian, so this is very old sedimentary rock but younger than most of the surrounding hard rock that composes various parts of the Canadian shield. Notably, the pink units mapped on the Boothia Peninsula are Paleoproterozoic in age (2.5-1.6 billion years old), potentially up to 2 billion years older than the limestones of King William Island.

(This is an absolutely massive .pdf file with some scaled features so I would recommend viewing via the official publication to actually read anything or see fine details: publications.gc.ca/pub?id=9.557274&sl=0)

Notably, this map was published in 2015, 8 years after the novel was written. However, according to the bibliography for the map (which can be accessed via the previous link) a preliminary geologic map has existed for the area since at least 1967, though I was unable to track this publication down online. The novel was clearly thoroughly researched and Dan Simmons could have easily accessed this publication and others through multiple institutions.

The surficial geology of King William Island has also been mapped, and is predominantly glacial, as one would expect given it's location. For those unfamiliar with glacial geology processes, this is basically saying that the bedrock is buried under a bunch of glacial deposits. Glacial till is composed of rocks and sediments plucked from the bedrock and ground up. This is why the surface of the island is not one big rock, but a bunch of smaller pieces. Interestingly, the material on the southern part of the island is sandier because it contains more material derived from the Canadian Shield further south. If you're interested in glacial geology, I highly recommend zooming around a bit on Google Earth because the features here are GORGEOUS.

(This map is absolutely massive and the lines scale with zoom so it's hard to see at this resolution, access it here: publications.gc.ca/pub?id=9.834073&sl=0)

(Google Earth Pro, satellite imagery from 2020)

According to the surface geology map and Google Earth, the actual landscape of King William Island is much more water logged than it appears in the show. It's not entirely impossible that there has been some geomorphological change since 1848, but most of the features mapped would have been formed during the last ice age and as the glaciers melted and not more recently. This would have been handy for the men of the Franklin Expedition because each of these pools is filled with freshwater.

Pag, Croatia

Tracking down a geologic map of Croatia was somewhat challenging as I don't speak Croatian. I was able to find a map of the whole country, and while it's all in Croatian the symbol for the geologic time periods is universal so time periods can be correlated. This shows that the units that make up Pag are Cretaceous and Paleocene-Eocene in age.

(Map accessed here: https://www.hgi-cgs.hr/en/geoloska-karta-republike-hrvatske-1300-000/)

I was able to find a .pdf (access here: http://kig.kartografija.hr/index.php/kig/article/view/158/274) that had a bit more information on the map above but at a lower resolution. This states that the Cretaceous units are dominantly carbonates from the Adriatic sea and the Eocene units are also carbonates. This makes sense as both the Cretaceous and Paleocene-Eocene boundary/PETM are times of increased global temperature correlated with increases in global sea level.

As always, the best geology website out there, Macrostrat, also came through on the unit lithologies. I was unable to access the source listed on Macrostrat, but both the Cretaceous (green) and Paleocene-Eocene units (orange) are listed as limestone.

(Source: https://macrostrat.org/map/#x=16&y=23&z=2)

One of the best views that we get of the geology on Pag is the last scene with Bridgens in episode 9. During the zoom out of this scene we get a really nice view of the bedrock and debris covering it.

Given all of this, I'm really not sure where the landscape description as shale came from. If there is historical precedence for calling the rocks on the island shale, let me know! I have read a few books but none of the primary sources from the expeditions to this region, so if it comes from that I wouldn't be surprised.

Overall though, I have to say that the filming location was well chosen given the similarities it holds to the geology of King William Island.

[sandypuggames]

in HELLPIERCERS, we represent the larger War of Infernal Liberation through a strategy phase called STRATCOM. This phase takes a ton of inspiration from map games, like A Quiet Year, as well as faction-focused TTRPGs like REIGN.

Each faction gets its own map to start with, and you will spend a lot of the game adding buildings, locations, traps, hazards, armies, convoys, and more to it in the same kind of collaborative-combative vibe as the rest of the game, with the GM trying to dominate Hell, push back your forces, and retake lost locations, and the players pushing up toward the final fortress of the enemy faction.

Each map is an abstraction, covering roughly a 800 mile stretch of territory that you'll grow into a complex visual log of The Last War.

First map is a representation of the SYNCRASIS faction's paleoproterozoic landscape, illustrated by the incredible @leafie-draws, and the second represents the industral-blasted nuclear wasteland of @leaftilde's AUTOPHYES faction, illustrated by the marquis of shadows, @jnbutlerart.

budget allowing I'd like to ship everyone two 11x17 trifolds with the maps printed, because Risk Legacy permanent changed my brain chemistry and i love the idea of physical maps covered in drawings and supply lines and armies and stuff.

How this side of the game plays out is very very much one of the more exciting elements of play, and I can't wait to see how you all engage with it. And remember, Hell is a prison. Break its bars.

[yee-qi]

Perspectives paleoart three, electric beegalee

"Filling the Hourglass" Francevillian Biota Paleoproterozoic, 2.1 billion years ago, Francevillian B formation (Gabon)

This is the Francevillian Biota! Might not be living, may or may not be eukaryotes, far too old to make sense of. If alive, they're notable for being some of the first multicellular organisms - a mysterious "precursor" branch that went extinct. Either that or they're just rock formations, but we can dream, right? They are being buried by silt from a delta.

This is part 2 of my Perspectives series! For more, check out #perspectives on my blog.

[sakuraswordly]

The Banded Iron Formation (BIF) near Gairloch, Scotland, is an ancient geological feature dating back to the Paleoproterozoic era, around 2.4 billion years ago. BIFs are distinctive sedimentary rocks consisting of alternating layers of iron-rich minerals and silica (typically in the form of chert), and they hold key clues to Earth’s early atmospheric and oceanic conditions. In Gairloch, the BIF is part of the Loch Maree Group, which is a sequence of metamorphosed volcanic and sedimentary rocks. This BIF formed during a time when the Earth’s oceans were rich in dissolved iron due to the lack of oxygen in the atmosphere. When oxygen started to be produced by photosynthetic microorganisms (such as cyanobacteria), it reacted with the iron in the oceans, precipitating out as iron oxide minerals. This process led to the formation of these alternating bands of iron and silica over millions of years. The Gairloch BIF is significant because it represents evidence of some of the earliest stages of oxygenation on Earth, known as the Great Oxidation Event (GOE). This event fundamentally changed the composition of the Earth’s atmosphere and oceans, allowing for the development of more complex life forms. The BIF also provides insights into the tectonic and volcanic activity during the early Proterozoic, as it is associated with volcanic rocks in the region. Due to its age and the tectonic activity that occurred in the area, the Gairloch BIF has undergone significant metamorphism. Despite this, the iron bands are still evident, and geologists study these formations to understand early ocean chemistry, the nature of ancient life, and the evolution of Earth’s atmosphere.

[parakaryote]

The Weird Microorganism Iceberg

I basically made this on an impulse, please don’t take it too seriously. Feel free to suggest more organisms!

Explanations under the cut.

Tardigrades: You probably all know this one. Commonly said to be polyextremophiles, but this isn’t actually true; while they can survive extreme conditions, they don’t thrive in them. Something you might not know about them is that all of their body segment genes are equivalent to arthropod head genes — meaning they are basically walking heads.

Demodex: Eyelash mites.

Diatoms: Geometric silicon shell creatures.

Nylon-eating bacteria (Paenarthrobacter ureafaciens KI72): Exactly what it says on the tin.

Myxozoa: Single-celled parasitic cnidarians. Lack digestive systems, circulatory systems, gonads, and even muscles in some species. Also may or may not be autonomous cancer cells.

Thiomargarita: The only macroscopic bacteria. Honorary microorganisms for the purposes of this image.

Wolbachia: Parasitic / mutualistic bacteria genus that has created numerous insect species through their effects on reproduction. (Infected females can become capable of parthenogenesis, while infected males are either killed, turned into females, or limited to reproducing only with females infected by the same strain.)

Deinococcus radiodurans: A bacterium which unofficially holds the title of “most extreme extremophile”. Can survive incredibly high doses of radiation, as well as high acidity and very low temperatures.

Dicyemida: Symbiotic (once mistakenly thought to be parasitic) animals that live in cephalopod kidneys. Have alternation of generations and used to be known as “Rhombozoa” (“rhombus animals”).

Facetotectans: Parasitic crustaceans with an unknown adult form. Attempts to artificially induce metamorphosis only produce another juvenile stage, as far as anyone can tell.

Metal-breathing bacteria: Bacteria which use nanowires to accept electrons from metals.

Limnognathia: One of the smallest animals, and has 15-part extensible jaws.

Disulforudis audaxviator: The only known organism to comprise a single-species ecosystem. Lives over a mile underground and feeds off the byproducts of radioactive decay.

Salinella salve: Possibly nonexistent simple animal, allegedly cultured by Johannes Frenzel in 1892 but never found by anyone else.

Warnowiids (Warnowiaceae): A family of dinoflagellates which have modified some of their organelles into an eye… which somehow works well enough for them to aim their stingers at prey, despite them having no brain (or even other cells) to process the images.

Haloquadratum walsbyi: A square that lives in salt.

Dicopomorpha echmepterygis: The smallest known insect, a parasitoid wasp smaller than a Paramecium.

Hemimastigophora: A group of organisms recently discovered to be an early-splitting branch of the eukaryotes.

Monocercomonoides: A genus of “excavate” “protists” (both terms are polyphyletic, lol) that lack mitochondria… or even the genes for them.

Parakaryon myojinensis: The only complete incertae sedis, for which not even the domain is known. Has an odd mix of eukaryote and prokaryote-like features, leading to speculation that they represent a second incidence of endosymbiosis (aka Eukaryota 2.0). Also my blog’s namesake.

Collodictyon: Considered unclassifiable for a long time. Not really that weird in and of itself, tbh.

Kamera lens: Continuing the theme, this is an alga that has proven weirdly difficult to classify despite having been known for centuries (though it’s been narrowed down to the Ochrophyta). Its funny name makes it a pain to look up.

Jeongeupia sacculi: Recently-discovered multicellular(!) bacterium. Unlike everything else on here, it doesn’t have a Wikipedia page (yet).

Meteora sporadica: “Protist” which moves by rowing with a pair of arm-like appendages. Another difficult-to-classify organism, although a study from earlier this year suggests they are related to the Hemimastigophora.

Kakabekia barghoorniana: Apparent Paleoproterozoic living fossil that looks like an umbrella.

Magosphaera planula: A sphere which splits apart into amoeba-like cells, observed by Ernst Haeckel in 1869. Also possibly nonexistent / misidentified.

[hellcatsandcars]

i don't get the "how many times do you think of the roman empire" trend because i've been hyperfixated on history since i was six. i think about it the same amount as i think about pre-colombian civilisations and the paleoproterozoic era. which is admittedly an insane amount, but it's my autism and i get to pick the music

[georgegraphys]

People are at another level of idiocy. Bringing up "George only won twice, (insert name here) won 192728373773 times"

One is in his sixth season, 5 of which spend in a non race winning car. The other has been in the sport since the paleoproterozoic precambium siderian age

This is like asking a newbie nugu country swimmer/tennis player/figure skater at their first olympic

"Why haven't you got as many medals as Michael Phelps/Serena Williams/Evgeni Plushenko/Yuzuru Hanyu?"

[jcmarchi]

Even the Oldest Eukaryote Fossils Show Dazzling Diversity and Complexity - Technology Org

New Post has been published on https://thedigitalinsider.com/even-the-oldest-eukaryote-fossils-show-dazzling-diversity-and-complexity-technology-org/

Even the Oldest Eukaryote Fossils Show Dazzling Diversity and Complexity - Technology Org

The sun has just set on a quiet mudflat in Australia’s Northern Territory; it’ll set again in another 19 hours. A young moon looms large over the desolate landscape. No animals scurry in the waning light. No leaves rustle in the breeze. No lichens encrust the exposed rock. The only hint of life is some scum in a few puddles and ponds. And among it lives a diverse microbial community of our ancient ancestors.

A soft summer evening in the Paleoproterozoic, as envisioned by DALL-E. Image credit: DALL-E, prompt by Harrison Tasoff.

In a new account of exquisitely preserved microfossils, researchers at UC Santa Barbara and McGill University revealed that eukaryotic organisms had already evolved into a diverse array of forms even 1.64 billion years ago.

The paper, published in the journal Papers in Paleontology, recounts an assemblage of eukaryotic fossils from an era early in the group’s evolutionary history. The authors describe four new taxa, as well as evidence of several advanced characteristics already present in these early eukaryotes. 

“These are among the oldest eukaryotes that have ever been discovered,” explained lead author Leigh Anne Riedman, an assistant researcher in UCSB’s Department of Earth Science. “Yet, even in these first records we’re seeing a lot of diversity.”

Eukarya forms one of the major domains of life, encompassing the plant, animal and fungi clades, as well as all other groups whose cells have a membrane-bound nucleus, like protists and seaweeds.

Many scientists had thought early eukaryotes were all fairly similar during the late Paleoproterozoic, and that diversification took place around 800 million years ago. But Riedman and her co-authors found fossils of a delightfully diverse, and complex, cast of characters in rock nearly twice as old.

Limbunyasphaera operculata is a new species that shows a small door opening into the cell. Photo Credit: Riedman et al.

Scientists knew from previous studies that eukaryotes had evolved by this time, but their diversity in this era was poorly understood. So Riedman headed to the Outback in late 2019. Within one week, she had collected about 430 samples from eight cores drilled by a prospecting company; they now reside in the library of the Northern Territory Geological Survey. The two cores used for this study spanned roughly 500 meters of stratigraphy, or 133 million years, with around 15 million years of significant deposition.

Riedman returned to the United States with shale and mudstone: remnants of an ancient coastal ecosystem that alternated between shallow, subtidal mudflats and coastal lagoons. A dip in hydrofluoric acid dissolved the matrix rock, concentrating the precious microfossils which she then analyzed under the microscope.

“We were hoping to find species with interesting and different characteristics to their cell walls,” Riedman said. She hoped that these features could shed light on what was happening within the cells during this time period. Reaching any conclusions about the cellular interior would require a great deal of sleuthing, though, since the fossils preserve only the exterior of the cells.

The researchers were surprised by the diversity and complexity preserved in these fossils. They recorded 26 taxa, including 10 previously undescribed species. The team found indirect evidence of cytoskeletons, as well as platy structures that suggest the presence of internal vesicles in which the plates were formed — perhaps ancestral to Golgi bodies, present in modern eukaryotic cells. Other microbes had cell walls made of bound fibers, similarly suggestive of the presence of a complex cytoskeleton.

The authors also found cells with a tiny trapdoor, evidence of a degree of sophistication. Some microbes can form a cyst to wait out unfavorable environmental conditions. In order to emerge, they need to be able to etch an opening in their protective shell.

Making this door is a specialized process. “If you’re going to produce an enzyme that dissolves your cell wall, you need to be really careful about how you use that enzyme,” Riedman said. “So in one of the earliest records of eukaryotes, we’re seeing some pretty impressive levels of complexity.”

Many people in the field had thought this ability emerged later, and the evidence for it in this assemblage further emphasizes how diverse and advanced eukaryotes were even at this early juncture.

“The assumption has always been that this is around the time that eukaryotes appeared. And now we think that people just haven’t explored older rocks,” said co-author Susannah Porter, an Earth science professor at UC Santa Barbara.

This paper is part of a larger project investigating early eukaryote evolution. Riedman and Porter want to know in what environments early eukaryotes were diversifying, why they were there, when they migrated to other places, and what adaptations they needed in order to fill those new niches.

A big part of this effort involves understanding when different characteristics of eukaryotes first arose. For instance, the authors are quite interested to learn whether these organisms were adapted to oxygenated or anoxic environments.

The former would suggest that they had an aerobic metabolism, and possibly mitochondria. Every modern eukaryote that’s been found descends from ancestors that possessed mitochondria. This suggests that eukaryotes acquired the organelle very early on, and that it provided a significant advantage.

Riedman and Porter are currently working on a fresh account of eukaryote diversity through time. They’ve also collected even older samples from Western Australia and Minnesota. Meanwhile, their geochemist collaborators at McGill are spearheading a study on oxygen levels and preferred eukaryote habitats, aspects that could shed light on their evolution.

“These results are a directive to go look for older material, older eukaryotes, because this is clearly not the beginning of eukaryotes on Earth,” Riedman said.

Source: UCSB

[vickysaurus]

The Prehistoric Nature mod for Minecraft had an update that greatly improves the Precambrian! Now instead of a simple two-biome world where Ediacaran critters live under Cryogenian ice, there's loads of different biomes from different parts of the Precambrian to explore. Unlike the other dimensions the mod adds, the Precambrian dimension has very few actual mobile creatures going about, and all of those seem to be in the Ediacaran biomes, so it feels suitably lonely. I'll put a bunch of screenshots below the cut in whatever order I end up encountering stuff.

Neoproterozoic Microbial Plains are covered in microbial crusts, which break when you walk over them, making them quite crunchy. The little pools that dot the landscape have both red and green algae living in them.

Hadean Volcanic Wastes are suitably fucked up.

The Cryogenian naturally has both the land and sea entirely frozen over. However, underwater there's more going on than in the biomes depicting earlier eras!

Paleoproterozoic Regolith, a quite martian-looking biome showing a time before any trace of life on land.

The Ediacaran biomes are much more lively than the others, with the seas covered in Charnia and its friends, while there's even some cretures crawling around between them and jellyfish swimming. I quite like these underwater chasms running through the biome I found.

Archaean tide pools have signs of life here and there in the form of stromatolites and microbial mats. Due to the lack of oxygen, the sky ranges from red to yellow depending on the weather. There's full Archaean sea biomes to be found as well.

Mesoproterozoic Carpet has plenty of Tawuia, Grypania, and of course stromatolites.

[aialaau]

Plants are Fucking Weird

This is a thought that has only just started to plague me, but I needed to infect others with it.

SO! We all know that plants and other photosynthesizers process oxygen, right? The thing that keeps our respirating asses alive? We've all seen the oversimplified diagrams.

And they can do that shit with only .04% of the atmosphere being CO2!

BUT! But. Plants still do cell respiration!

Meaning that they still need oxygen! Clearly less than what they produce as evidenced by the vast majority of the animal kingdom being oxygen sinks and the atmosphere still sitting comfortably at 21% oxygen.

I just think it's fucking wild that entire swatches of Earth's biosphere are dependent on the fact that plants are massive overproducers of a highly reactive and explosive gas that they need themselves to survive.

And don't even get me started on the Great Oxygen Catastrophe of the Paleoproterozoic.

[baglsasha]

Do you even know how many non air breathing organisms died in the oxidation of earth during the paleoproterozoic era??? The absolute ignorance...

reblog if you think that it is probably morally okay to breathe air

[cornehoward-blog-blog-blog]

Certainly! A research paper on the geological history of the Precambrian period, specifically focusing on the Hadean, Archean, and Proterozoic eons, will be a fascinating exploration. I'll provide an in-depth look into the major events, dates, and significant milestones that took place during this time. Let's delve into the details:

Title: "Exploring the Geological History of the Precambrian Period: A Comprehensive Analysis of the Hadean, Archean, and Proterozoic Eons"

Abstract:

The Precambrian period marks a vast expanse of time in Earth's history, encompassing nearly 4 billion years of geological evolution that shaped our planet in profound ways. This research paper delves into the geological history of the period, with a particular focus on the Hadean, Archean, and Proterozoic eons. Detailed analyses of major events such as the Great Impact Event, the Late Heavy Bombardment, the emergence of life, and other significant geological developments offer valuable insights into the Earth's early stages.

1. Introduction:

- Definition and chronology of the Precambrian period

- Importance of studying the Hadean, Archean, and Proterozoic eons

2. Hadean Eon:

- Primordial Earth's formation and differentiation

- The epoch of intense meteoritic bombardment and the Late Heavy Bombardment event

- Investigating the hostile conditions and volatile atmospheric composition

3. Archean Eon:

- Establishing early crustal formations and stabilizing continents

- Influential tectonic processes: plate tectonics and formation of Supercontinents

- The rise of stromatolites and the appearance of first microbial life forms

4. Proterozoic Eon:

- Evolution of the Earth's atmosphere: oxygenation and the Great Oxygenation Event

- Origin and diversification of eukaryotic life forms

- Notable events and fossil records: Paleoproterozoic glaciations, the Algid Belt Supercycle, Ediacaran biota

5. Geological Events and Impact:

5.1 Great Impact Event:

- Analysis of evidence and theories surrounding the origin of the Moon

- Impact Craters: identifying prominent examples and their impact on the geology

5.2 Late Heavy Bombardment (LHB):

- Investigation into the late-period heavy meteoritic activity

- Discussion around the LHB's influence on shaping the Moon and Earth's surface

6. Emergence and Evolution of Life:

- Fossil record of Cyanobacteria and other early life forms

- Proterozoic fossil occurrences: acritarchs and early multicellular organisms

- Significance of ancient stromatolite formations

7. Conclusion:

- Overview of significant geological events and accomplishments during the Precambrian period

- Key takeaways and implications of studying the Hadean, Archean, and Proterozoic eons

- Discussion of avenues for future research within Precambrian geology

By extensively researching and considering the geological, paleontological, and astronomical evidence in this academic paper, this study aims to provide a comprehensive understanding of the overarching geological history of the Precambrian period, highlighting the significance of the Hadean, Archean, and Proterozoic eons.

Now that you have the structure and overview of the paper, would you like me to proceed in writing the complete research paper focusing on the geological history of the Precambrian period? Just let me know!

[nintendont2502]

Natural nuclear fission reactor

A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions occur. The conditions under which a natural nuclear reactor could exist had been predicted in 1956 by Japanese American chemist Paul Kuroda.[1] The remnants of an extinct or fossil nuclear fission reactor, where self-sustaining nuclear reactions have occurred in the past, can be verified by analysis of isotope ratios of uranium and of the fission products (and the stable daughter nuclides of those fission products). An example of this phenomenon was discovered in 1972 in Oklo, Gabon by French physicist Francis Perrin under conditions very similar to Kuroda's predictions.

Oklo is the only location where this phenomenon is known to have occurred, and consists of 16 sites with patches of centimeter-sized ore layers. Here self-sustaining nuclear fission reactions are thought to have taken place approximately 1.7 billion years ago, during the Statherian period of the Paleoproterozoic, and continued for a few hundred thousand years, probably averaging less than 100 kW of thermal power during that time.[2][3][4]

History

In May 1972 at the Tricastin uranium enrichment site at Pierrelatte in France, routine mass spectrometry comparing UF6 samples from the Oklo Mine, located in Gabon, showed a discrepancy in the amount of the U-235

isotope. Normally the concentration is 0.72% while these samples had only 0.60%, a significant difference (some 17% less U-235 was contained in the samples than expected).[5] This discrepancy required explanation, as all civilian uranium handling facilities must meticulously account for all fissionable isotopes to ensure that none are diverted to the construction of nuclear weapons. Furthermore since fissile material is why people mine uranium, a significant amount "going missing" was also of direct economic concern.

Thus the French Commissariat à l'énergie atomique (CEA) began an investigation. A series of measurements of the relative abundances of the two most significant isotopes of the uranium mined at Oklo showed anomalous results compared to those obtained for uranium from other mines. Further investigations into this uranium deposit discovered uranium ore with a U-235 concentration as low as 0.44% (almost 40% below the normal value). Subsequent examination of isotopes of fission products such as neodymium and ruthenium also showed anomalies, as described in more detail below. However, the trace radioisotope U-234 did not deviate significantly in its concentration from other natural samples. Both depleted uranium and reprocessed uranium will usually have U-234 concentrations significantly different from the secular equilibrium of 55 ppm U-234 relative to U-238. This is due to U-234 being enriched together with U-235 and due to it being both consumed by neutron capture and produced from U-235 by fast neutron induced (n,2n) reactions in nuclear reactors. In Oklo any possible deviation of U-234 concentration present at the time the reactor was active would have long since decayed away. U-236 must have also been present in higher than usual ratios during the time the reactor was operating, but due to its half life of 2.348×107 years being almost two orders of magnitude shorter than the time elapsed since the reactor operated, it has decayed to roughly 1.4×10−22 its original value and thus basically nothing and below any abilities of current equipment to detect.

This loss in U-235 is exactly what happens in a nuclear reactor. A possible explanation was that the uranium ore had operated as a natural fission reactor in the distant geological past. Other observations led to the same conclusion, and on 25 September 1972 the CEA announced their finding that self-sustaining nuclear chain reactions had occurred on Earth about 2 billion years ago. Later, other natural nuclear fission reactors were discovered in the region.

Mechanism

The natural nuclear reactor formed when a uranium-rich mineral deposit became inundated with groundwater, which could act as a moderator for the neutrons produced by nuclear fission. A chain reaction took place, producing heat that caused the groundwater to boil away; without a moderator that could slow the neutrons, however, the reaction slowed or stopped. The reactor thus had a negative void coefficient of reactivity, something employed as a safety mechanism in human-made light water reactors. After cooling of the mineral deposit, the water returned, and the reaction restarted, completing a full cycle every 3 hours. The fission reaction cycles continued for hundreds of thousands of years and ended when the ever-decreasing fissile materials, coupled with the build-up of neutron poisons, no longer could sustain a chain reaction.

Fission of uranium normally produces five known isotopes of the fission-product gas xenon; all five have been found trapped in the remnants of the natural reactor, in varying concentrations. The concentrations of xenon isotopes, found trapped in mineral formations 2 billion years later, make it possible to calculate the specific time intervals of reactor operation: approximately 30 minutes of criticality followed by 2 hours and 30 minutes of cooling down (exponentially decreasing residual decay heat) to complete a 3-hour cycle.[6] Xenon-135 is the strongest known neutron poison. However, it is not produced directly in appreciable amounts but rather as a decay product of Iodine-135 (or one of its parent nuclides). Xenon-135 itself is unstable and decays to Caesium-135 if not allowed to absorb neutrons. While Caesium-135 is relatively long lived, all Caesium-135 produced by the Oklo reactor has since decayed further to stable Barium-135. Meanwhile Xenon-136, the product of neutron capture in Xenon-135 only decays extremely slowly via double beta decay and thus scientists were able to determine the neutronics of this reactor by calculations based on those isotope ratios almost two billion years after it stopped fissioning uranium.

A key factor that made the reaction possible was that, at the time the reactor went critical 1.7 billion years ago, the fissile isotope U-235 made up about 3.1% of the natural uranium, which is comparable to the amount used in some of today's reactors. (The remaining 96.9% was non-fissile U-238 and roughly 55 ppm U-234.) Because U-25 has a shorter half-life than U-238, and thus decays more rapidly, the current abundance of U-235 in natural uranium is only 0.72%. A natural nuclear reactor is therefore no longer possible on Earth without heavy water or graphite.[7]

The Oklo uranium ore deposits are the only known sites in which natural nuclear reactors existed. Other rich uranium ore bodies would also have had sufficient uranium to support nuclear reactions at that time, but the combination of uranium, water and physical conditions needed to support the chain reaction was unique, as far as is currently known, to the Oklo ore bodies. It is also possible, that other natural nuclear fission reactors were once operating but have since been geologically disturbed so much as to be unrecognizable, possibly even "diluting" the uranium so far that the isotope ratio would no longer serve as a "fingerprint". Only a small part of the continental crust and no part of the oceanic crust reaches the age of the deposits at Oklo or an age during which isotope ratios of natural uranium would have allowed a self sustaining chain reaction with water as a moderator.

Another factor which probably contributed to the start of the Oklo natural nuclear reactor at 2 billion years, rather than earlier, was the increasing oxygen content in the Earth's atmosphere.[4] Uranium is naturally present in the rocks of the earth, and the abundance of fissile U-235 was at least 3% or higher at all times prior to reactor startup. Uranium is soluble in water only in the presence of oxygen.[citation needed] Therefore, increasing oxygen levels during the aging of the Earth may have allowed uranium to be dissolved and transported with groundwater to places where a high enough concentration could accumulate to form rich uranium ore bodies. Without the new aerobic environment available on Earth at the time, these concentrations probably could not have taken place.

It is estimated that nuclear reactions in the uranium in centimeter- to meter-sized veins consumed about five tons of U-235 and elevated temperatures to a few hundred degrees Celsius.[4][8] Most of the non-volatile fission products and actinides have only moved centimeters in the veins during the last 2 billion years.[4] Studies have suggested this as a useful natural analogue for nuclear waste disposal.[9] The overall mass defect from the fission of five tons of U-235 is about 4.6 kilograms (10 lb). Over its lifetime the reactor produced roughly 100 megatonnes of TNT (420 PJ) in thermal energy, including neutrinos. If one ignores fission of plutonium (which makes up roughly a third of fission events over the course of normal burnup in modern humanmade light water reactors), then fission product yields amount to roughly 129 kilograms (284 lb) of Technetium-99 (since decayed to Ruthenium-99) 108 kilograms (238 lb) of Zirconium-93 (since decayed to Niobium-93), 198 kilograms (437 lb) of Caesium-135 (since decayed to Barium-135, but the real value is probably lower as its parent nuclide, Xenon-135, is a strong neutron poison and will have absorbed neutrons before decaying to Cs-135 in some cases), 28 kilograms (62 lb) of Palladium-107 (since decayed to Silver), 86 kilograms (190 lb) of Strontium-90 (long since decayed to Zirconium) and 185 kilograms (408 lb) of Caesium-137 (long since decayed to Barium).

Relation to the atomic fine-structure constant

The natural reactor of Oklo has been used to check if the atomic fine-structure constant α might have changed over the past 2 billion years. That is because α influences the rate of various nuclear reactions. For example, Sm-149 captures a neutron to become Sm-150, and since the rate of neutron capture depends on the value of α, the ratio of the two samarium isotopes in samples from Oklo can be used to calculate the value of α from 2 billion years ago.

Several studies have analysed the relative concentrations of radioactive isotopes left behind at Oklo, and most have concluded that nuclear reactions then were much the same as they are today, which implies α was the same too.[10][11][12]

Yk what I asked for unhinged - can I really complain about. Whatever this is?

Anyway thanks anon for finally pushing me to add "long post" to my filtered tags because god knows I refuse to read anything this long and educational