This is the official RU-vid channel for Virtual Seminars in Precambrian Geology (VS-PG - sign up to attend the weekly Zoom seminars on the website home page - sites.google.com/ucr.edu/vs-pg/home). Each presentation from the seminar series will be posted publicly here.
Let the record show that at a certain point about midway through this talk--as the basic point about nearshore facies control of the 13 C excursion became clear--I spontaneously yelled "life" so that would agree with the gut level referral to paleobiology! (I think something related to all this is discussed by Paul Smith here ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-blN-F8n2IAc.html -- but I'm not entirely sure)
Risun, step back a moment and think about "all the basic body plans" for modern animals exploding in the Cambrian, AREN'T THEY ALL REALLY JUST COMPLICATED WORMS? I just don't see that complexity and diversity NOT being preceded by Worm Wars, ie, enough predation to cause that development and diversity. That said, the "late Ediacaran" is a LONG period of time, the Worm Wars could have been at the very end of the Ediacaran, but dunno, macro worm tracks were possibly found back in the Cryogenian, and worms evolving, and predating, as sub and barely macro creatures likely wouldn't leave a trace. Just saying.
Ediacaran WORM WARS! The combination of population bottlenecks from extinctions PLUS intense predation amongst worms during the Ediacaran is the best explanation for the incredible variety of worm-based body plans getting macro sized in the Cambrian. Cmon guys, predation equals diversity, teeny worms eating each other during hard times in the Ediacaran microbial mat becomes the Cambrian, too many basically worm-based body plans with funky shields and appendages in the Cambrian to make sense without intense predation in the Ediacaran, Imho. The worms just got bigger, and started using the newly available minerals (calcium carbonate esp.) in the late Ediacaran and early Cambrian. Clams, lobsters, fish, lions, just worms with a lot of stuff added on, think about it, duh😆
I like the conclusions but I still feel it’s putting the effect before the cause. To me, if we’re seeing higher amounts of oxygen and low surface-area to volume (or bigger) animals in the White Sea Assemblage transitioning to lower amounts of oxygen and higher surface-area to volume (or smaller animals then we may be seeing a boom and bust cycle. I can’t remember which lecture I’d heard it from but it was pointed out that trace fossils of bacterial mat grazers started very random and aimless and became more efficient throughout the Ediacaran. At the very least that hints at population increase and population specialization during the White Sea Assemblage that collapsed into smaller more generic animals during the Nama Assemblage. I think that pushes back the driver of evolution during the Cambrian, intensive predation of animals upon other animals, into the latest Ediacaran. Thus the only real difference is that the earliest Cambrian is showing us evidence of animals reactions to the desperate conditions of the Nama Assemblage and an appearance of predation of biomineralization and bioturbation.
This is fantastic reference for programmers and developers for a serious project on ediacaran life and environments in that era for the gaming industry. We need more of these presentations ( not just as inspiration) but as a resource of examined data- turned into believable concepts / theory. Outstanding !
The most under rated time period 🎉. Thanks for the update ❤😊 And, the intense delivery…this is a very intelligent person! 🎉. I had to check to see if I left it on 1.5 speed. 😂. Just fascinating and tremendous how much the human collective has been able to reassemble the past. 🎉. I also thought only guitar players debated Germanium vs Silicon (the materials that transistors in our fuzz pedals are made from) ❤😊
I cannot believe anyone who starts out with the continents all in their present form, however mashed up, because all continents show many signs of having collided, smashed into one another, and otherwise violently assembled. The world of 10,000 years ago would be unrecognizable to overwhelming numbers of modern "experts". Dinosaurs were not built for elevation increases (ignore Jurassic Park), or for crossing wide rivers. Oceans probably did not exist that long ago (more than 5,000 years), and mountain ranges like the Big 5, the Andes, Himalayas, Rockies, Altais, and Alps, were not yet uplifted. It really doesn't matter IF one "finds" a fossil at the 20,000 foot elevation, mostly because WHEN it was encased in mud, the area it occupied WAS well "below sea level". Seas are shallow bodies, oceans are depths, and Earth had no (or at most one -- a VERY small Pacific) oceans, before less than about 5,000 years ago. It took time (centuries) for the water to "run off" (or puddle up in low-lying areas, depressing them with the sheer weight of water -- 62.4 pounds per square foot). More water arrived, a couple hundred years later, adding to the problem, and five hundred years after that, more water arrived. The Sphinx shows signs of water erosion at its base (from sitting water), and it sits more than 100 vertical feet above flood stage! That's a mega-flood, if it was a flood (it wasn't), and it isn't alone in its testimony for a different past than we're told. The ancient past, before the 8th Century BC becomes progressively murkier, the further back one goes. Modern writers refer to Moses and Solomon as "mythic", because it has been so long since their time, and humans don't do well with time. It overwhelms our senses, excites our worst fears, and threatens our stability. We avoid dealing with it in any way that doesn't minimize its power. South America specifically did not look like it does, today, much more than about 3,600 years ago, perhaps a couple centuries less. Something rolled up its "western" side, pushing up the Andes. We have a story in the Bible about an event that would have resulted in that, at the least (and a whole spectrum of other consequences), but geologists do not pay attention to the Bible, except to pay lip service. The Old Testament, the Hebrew Bible, essentially, is a collection of "survivor stories", left to us by those who lived through Earth's conflict with a Big Dumb Rock, a series of events that left the BDR "tidally-locked" with Earth for the last 2,750 years +/- 50. That condition puzzled astronomers for a long time, as they tried to figure out the body's "day", its rotational period. At one time, I recall reading it's day was longer than its year. We know, now, of its condition, one that explains the confusion, and supports my contentions. NASA is sending a mission to determine what it does, when it's on the other side of the Sun from Earth, whether it rotates on its own, or stops. The events of the past are not "myths", "legends" and "Bible stories", they are voices from long ago, telling us what happened to them. As I've aged, I've given thought to how I could pass down what I consider important, and it is a daunting task, to get more than a couple hundred years. I have a family Bible, from 1673, but the writing in it, of my family of 350 years ago, is in Old German, not easily translatable (I haven't found anyone yet), and the pages are disintegrating. Decrepitude affects everything put together. We call it "entropy", or "Everything put together falls apart". The ancient Egyptians who built the Sphinx, and the Pyramids at Giza, found a way to get the message across almost 5,000 years, but there is controversy about what they were trying to say. Similarly, the Mayans who created the Calendar, about 3,000 years ago, or more, left us wisdom burned by Spaniard "priests", highlighting the other danger, humans themselves. Not merely time, but the ignorance at the heart of our species, has done more to obfuscate the past. It was not a safe, comfortable, or enjoyable ride, much of the time!
l love your work and I love this channel. Please keep posting. Vox loco et solo clamantis est in deserto. The comparison of the Superior circular structures to those on Venus seems to imply (perhaps unintentionally) the notion of stagnant lid processes for Earth in the late Archaean. I believe we were way past stagnant lid at the time of these events (2.73 Ga). My own sense is that if we ever had stagnant lid, it was Hadean and it is ALL gone. The Acasta Gneiss might be trying to tell us any such regime ended quite early. Even Pilbara doesn't seem to fit my notion of stagnant lid. I instinctively view Stagnant Lid to imply horizontally "stagnant mantle", characterized by vertical pinpoint plume motions with attendant smaller scale lateral displacements to accommodate the rising plume material. The Venusian domes are then just igneous blobs formed at the surface by plume burps. (That's if we can conclusively rule out their origin as bolide punctures.) They erupted onto some crust about which I know nothing, but they don't appear to be foundering. Might be that crust is thick. Venus' mantle could be monominerallic for all I know. In that (unlikely) scenario, magma and source rock are the same composition; density differences arise only from temperature and pressure, not fractional melting and crystallization. That would make for a lot less action. I don't care who you are, that's funny. What we're seeing in the granite/greenstone terranes is straight up lava lamp action generated without hemispherical scale lateral motions of the mantle. Hans Ramberg had it all back in '67. The lava lamp model obviously needs to be extended to incorporate polyphasic rocks subject to repeated episodes of partial melting, melt extraction, and large scale chemical differentiation in addition to diapiric rise and cold foundering. Rocks from this era are commonly highly deformed by what appear to horizontal forces, and if not plate tectonics, then what? Tectonics done it alright, just not "plate" tectonics. Perhaps most of what we argue about could be simply settled by allowing for small plates. Early cratons might have had no connection to their adjoining oceanic slabs, instead just pushing them around and possibly forcing them under the cratons (underplating) instead of descending into the mantle slab graveyard. Oh, BTW, if anyone can tell me how the craton is attached to the plate at its edge, I'm all ears. How does slab pull drag a craton around? Bob? Kent? Watch video of slag circulation on molten metal, and see how it changes over time if the charge is allowed to cool in the crucible. Tectonics in real time, baby! I think we're looking at a phase between a presumed stagnant lid and modern Paleozoic-style tectonics. We need a name for this regime: I'll suggest we call it the "Rambergian Phase". It pretty much corresponds to the Archaean. All of the data you've presented, (which by the way is great, great work) coupled with everything else we know seem to indicate a vigourously convecting mantle, but with a stronger vertical component relative to the horizontal. All I'm getting at is that the Venus comparison is kinda tenuous. Sorry. Now for the real fun. The graphic of the plume ponding under the SCLM and then working its way upward along the upward tapered bottom of the SCLM had me jumping! If I was a plume, that's exactly what I would do. I can never figure out if the igneous rocks we see are the plume material itself or SCLM melts produced by the plume heat. Either way I believe they behave and rise in the same manner: Plume causes rifted margin; rifted margin is multiply intruded along the normal faults by gabbroic magmas. But, importantly, a rifted margin is not a simple hard break. The edge of a rifted craton is a broken mess of fault blocks often extending hundreds of kilometers across strike. There's plenty of room for complexity as to where the intrusions will emplace. Your description of the plume material rising under the cratonic edge is how I picture the anorthosites formed, particularly the Grenville series. Thus the Anorthosite line is a rough approximation of the cratonic edge location after it was rifted apart. My best guess is that most of what we see in these mafic intrusions are melts derived from the SCLM and not the rising plume material itself. I wonder if HREE depletion in OPX could inform us on that question. I also guess that at the depth of the craton here, 75 through about 25 kilometers, plagioclase floats. After it rises to shallow emplacement depths it becomes mildly negatively bouyant and sinks. What neither I nor anyone else can explain is why Anorthosites (massif-type) are confined to the late Proterozoic. Best guess is that the phenomenon of plumes rising under the edge of a craton has been going on since cratons first went into business for themselves, but the petrological manifestation has evolved over time. First it's them damn greenstones, then it's your garden variety ultramafics, and then for a very short window, Anorthosites. All corresponding to gradual earth cooling and thickening of the lithosphere. Happy.
I find it hilarious that a distinguished scientist, who searches the globe for biological truth, feels compelled to play along with the latest social psychosis de jour by feeling it necessary to announce that he's a "he/him". Too funny.
Thank you for a very interesting presentation. I am in my 70's but a beginner in Geology, so although my questions are roughly about silica and maybe 'off topic' (and seem very basic) I would value a knowledgable reply based on accepted uptodate papers etc. Questions At what time during the Hadean? would we start to see sand appearing? My understanding is that rocks need time and erosion to break down crust via weather/climate/wind? to silica forms like sand. Or is there any other reason ? e.g. is the early bombardment also depositing a water buildup and the cause or increase of erosion . I guess I am also curious about why today there's not red seas from the huge amounts of early pyrite, and not what i see today a sedimentary sand in the oceans often pale or yellow.. Sorry about my ignorance but I would value you straightening me out. Thanks
How did a lecture on ediacaran evolution evolve into a pro for Marxism. And this comment got a like. Im like 99.8% it was the person writing the comment. Communism is great on paper like in Marxs book but put it into the world and it fails.
Is there a systematic bias againat the preservation of shallow-water ecosystems of "Avalon" age? Do you think there was there a genuine absence of "White Sea"-type animals living in shallow water during that time, or do you expect that the faunas overlapped with each other?
Great data presentation and volume of data as well.......Just not really strong enough to connect the dots. Serious. Am disappointed at weakness when conclusions are attempted to be made.
I have an example from the gasconade formation in dent county Missouri. It has several types of tubes, some plated some not. There's also a silica gastropod or two. And quartz replacement of soft tissue.
Truly enjoyed this lecture. Thank you for all the work you do illuminating the Ediacaran, a particularly fascinating and underappreciated period of Earth's biological history.
I have found a few specimens of charnia in cherty flint from the thames foreshore in london,maybe they would be interesting to you.all english flint is Cambrian or is that now rong?
From an amateur eye, I think you are looking at the results of the Frankenstein progression. For billions of years there wasn't oxygen and single cell organisms could clone and prosper. The accumulation of oxygen became toxic to them, and through cloning they passed on the oxygen deformation to the clones decreasing the clones life span. Which is why sexual reproduction evolved through cells splitting only half their code and requiring a second partial code from another in order to break the oxygen deformation inheritance. Anyways there's banded iron formations from several events prior and throughout the time you are looking at. The constant fluctuating oxygen levels and the struggle for evolution to adapt in altering conditions left it grasping at every direction and likely some blue prints just didn't last. You should consider volcanism, hydrothermal vents and meteor impacts as a combination of environmental services influences and failed biological attempts to adjust. You can't have worms with no mouths or buttholes surviving through energy created by ancient bacteria inside them without major influences on a variety of magnitudes. Scientist need to broaden their time focus and understand geologic time in ancient history is all relevant to any particular time period. There wouldn't be a tsunami recorded in the early Cambrian bonneterre formation of Missouri if there wasn't geologic driving forces involved. Earth's evolution and life's evolution are hand and hand. Y'all have proven that much. There was a great struggle when oxygen formed in the water and the over oxygenated material of the ocean occured before the atmosphere. Everything had to overcome that and when it did, it had it's oxygen stripped away.. repeat that a few times while trying to recode and evolve. The answers are out there. And everything is evidence. Cold, hot, oxygen fluctuations, continental formations, ancient bacteria from asteroid impacts deep in oceanic crust mixing with evolved bacterias in the sub sedimentary ocean layers, it's endless. Great start to piling evidence and pushing for more answers ❤❤❤
Can please someone explain why Eu and Ce anomalies of seawater are recorded in carbonates and Fe-Mn BIFs? Shouldn't they be opposite? If you could redirect me to some resource it will be highly appreciated
There's a tsunami in the rock record above the great unconformity in Missouri. I think much is lost in the understanding of the Ozarks, prior to the Ouachita. Personal I think this part of the key to figuring more details. I also believe there was hydrothermal activity, ancient volcanism, shoreline rifting etc. Stories of part of Texas and Oklahoma trying to rift apart, and failing like the older rifting in the great lakes
It's likely. Aerobes were thought to have evolved in the last billion years, and would have followed the trends of oceanic and atmospheric oxygenation.
@@Denny_Boi Thank you for taking time to reply. I'm not an expert, just some random guy on the internet who is curious. If I understand correctly, recent developments in the study of prokaryotes suggest the very first eukaryotes could process oxygen. We discovered archaea are the prokaryotes most closely related to the nuclear DNA of eukaryotes. Then we found Lokiarchaeota, a group an anaerobic archaea that parasitize aerobic bacteria to gain aerobic abilities, like how our nucleus depends on mitochondria... And don't the genetic estimates for the origin of eukaryotes go back to about 2 billion years? I heard people suggest in parts of the ocean where light can reach, photosynthesizers may have produced small amounts of oxygen that was used up by aerobic bacteria & aerobic eukaryotes before it could diffuse very far. IDK if that is correct, but it's very interesting.
