We have radiometric detrital dating of 4.0 Ga for the Inukjuak Domain east of the northeast Superior craton in Canada and for the Slave craton in the Northwest Territories in Canada, zircon crystal datings of ~4.27 Ga for the Yilgarn craton in Western Australia, possibly ~4.0 Ga for the Pilgangoora Belt of the Warrawoona Group in the Pilbara craton in Western Australia, over 3.8 Ga for the Isua greenstone belt in Western Greenland, and over 3.6 Ga for the Barberton greenstone belt in the Kaapvaal craton in South Africa. Did I forget any? There has to be a connection amongst these cratons to an early ca. ~4.0 proto-supercontinent or supercontinent. It's highly unlikely that at some point in time they would not have merged.
Wow, I didn't know they had so many of these early dates. But I don't see how you arrive at the conclusion that they must have merged. I mean that far back there was a lot less continental material, right? The continents were itsy-bitsy little things. Plus the convection cells in the mantle were probably quite different from today, right? I think I've read that there were probably more of them, so that there were lots of little sialic rafts getting created, that we would be reluctant to call a continent today. So, in that scene what makes you think they would have all got together for a big party?
We had the continental material, crust evolution, back then. Similar dating is arrived at by over twenty different ways of radiometric dating comparisons, mineral ratios, latitude and longitude positions, aeromagnetics, and what they call SHRIMP analysis results. Convection cells in the mantle is the problem that I'm having because it couldn't have existed before the Earth's iron core was in place and we're not sure of the exact date of that. Somewhere around ~4 billion years ago. Before that there were probably lots of upper mantle plumes and hot spots creating continental crust. We can trace parts of the individual cratons back to 4 Ga in many locations around the world, but were they connected back then? How to piece it together that far back is the problem. But I'm finding evidence in the literature that they can infer whether or not that old of crust was formed in an aqueous environment or not, so that's a step forward. In other words, early underwater volcanic eruptions could have also led to early continental crust. There's no doubt that there were continents on Earth before 4 Ga. The problem as I see it is - and as you state - were they connected into a supercontinent earlier than the supercontinent Valbaara at ~3.3 Ga, or before that only itsy-bitsy little things, like island arcs.
Hipparchia: thanks for your comment, and you really do strike at the heart of the problem. I just came across this article relevant to early convection currents and the evolution of continental crust: "Hadean and Archean crustal processes: The processes that controlled crustal formation during the first Hadean era (pre-3.8 Ga) and the Archean (~3.8 to 2.5 Ga) remain an area of active debate. It is now generally acknowledged that the earliest Hadean was characterized by core formation and partial melting of the outer mantle [note: during the early formation of the Earth the outer layer froze over - solidified]. The terrestrial magma ocean phase (like the corresponding lunar magma ocean) was probably short-lived and frozen by ~4.44 Ga – a period we refer as the Tartarean. After the Tartarean magma ocean phase, heat flow would have remained high throughout the Hadean and much of the Archean, driving vigorous thermal convection of the mantle by heating from below and forming a large number of small crustal plates. Thermal convection driven from below physical are characterized by plume-like upwellings that bring heat to the surface. These thermal plumes are consistent with models for Archean komatiite formation that suggest oceanic plateaus. since these features are thought to represent plume volcanism in an intra-oceanic setting. If the melting that forms komatiites occurs under dry conditions, mantle potential temperatures of ≈1500º to 1700º C are implied – hotter than modern plume heads, and consistent with an Archean mantle that was hotter than today’s, thermally buoyant, and actively convecting. In contrast, these same models of thermal convection are characterized by the sinking of cooler lithospheric plates along vertical zones of convergence, with material from both sides of the convergence zone sinking back into the hot asthenosphere symmetrically. Modern, asymmetric convergence, which is driven by the sinking of cold lithospheric plates is not observed, and may not have occurred in the Hadean or early Archean. A speculative model for the formation of greenstone belts at the sites of plume-like up-wellings from the mantle, and their preservation at zones of convergence, along with TTG suite granitoids formed by partial melting of the sinking mafic crust is assumed. This model is based on the pure thermal convection model with hot plumes rising from the core-mantle boundary and melting to form a proto-oceanic crust that is thicker than modernoceanic crust, and resembles oceanic plateau crust. This is consistent sinking of this proto-oceanic crust at zones of convergence and is essentially vertical and symmetrical along convection cell walls.This model has some interesting implications. First, geometric constraints require that the thick proto-oceanic plateau formed above the rising plume must spread laterally as it moves radially away from the rising plume, in order to preserve crustal volume as the surface area increases. This spreading will be viscous in the lower crust and brittle in the uppermost crust, where normal faulting should be common. As a result, the preserved crustal thicknessshould be much thinner than the primary thickness of the plateau (<15% of the original thicknessfor spreading over two radii of the original plateau). Second, convergence at triple junctions where three cells meet will focus this radial flow back into a single descending “anti-plume”; converging proto-oceanic crust may tend to be preserved here, especially if the position of this triple-junction is unstable. This will preserve the proto-oceanic crust (possible greenstonebelts?) as small, deltoidal blocks, sitting above the triple junction and subject to compressivestress during convergence. Proto-oceanic crust that does sink (i.e., most of it) will be strongly deformed by this convergence and partially melt to form TTG suite magmas that will rise and intrude the overlying greenstone belt. The residue of this melting will be eclogite similar to that formed by subduction processes today.The implication of this thermal convection model is that even though mafic crust resembling modern oceanic crust, or oceanic plateaux, may have formed, there is no assurance that this crust was destroyed along Phanerozoic-style, asymmetrical subduction zones. Sinking of mafic and ultramafic crust along vertical convergence zones would still recycle crustal material back into the mantle, preserving the chemical and isotopic traces of this process, and preserving remnants of this mafic crust as eclogite. So evidence for the existence and recycling of oceanic-like crust does not conclusively show that modern style plate tectonics was operative.The preservation of oceanic crust at symmetrical convergence zones is likely to involve significant deformation and thrusting, forming schüppen zones of imbricate thrust slices of oceanic crust that stack older crust onto younger. These thrust complexes would not resemble modern accretionary complexes." http://72.14.203.104/search?q=cache...tone belt" superior&hl=en&gl=us&ct=clnk&cd=13 Initially earth formed from a gaseous-particle cloud and had a molten magma ocean surrounding its entire outer layer. This froze over until the molten iron core was formed to generate heat that melted it. Then the cycle of the evolution of continental crust began. There had to be a larger continent before the ~3.3 Ga supercontinent Valdaara, rather than just bits and pieces or plume mantle island arcs, because the iron core probably was well in place by ~4.0 Ga.
I would logically expect the early mantle to be hotter than today's. I don't understand the reasoning for suggesting dry conditions. Not only would the early mantle have been hotter, it would also have been wetter and more gaseous than today's mantle. So the presence of komtatiites does not seem to be evidence for a hotter mantle. Isn't the writer here being incorrect. Surely a triple junction is the junction of three plates, not the the junction of three cells. I don't understand what you are saying here. The formation of the molten iron core caused the outer crust to melt again? That doesn't make sense to me. Can you explain what you mean please. And here I don't understand the connection you are making between the formation of the core and the presence of a supercontinent. Please expand and explain. This is all very interesting.
crust movement at 15 cm per year would take 268,224,000 years to move 25,000 miles 268,224,000years = 25,000 miles 134,112,000 years = 12,500 miles 67,056,000 years =6250 miles 33,528,000 years =3125 miles 16,764,000 years =1562.500 miles 8,382,000 years =781.250 miles 4,191,000 years =390.625 miles 2,095,500 years =195.312 miles 1,047,750 years =97.656 miles 523,875 years =48.828 miles 261,938 years =24.414 miles 130,969 years =12.207 miles 65,484 years =6.103 miles 32,742 years =3.051 miles 16,371 years =1.525 miles 8,186 years =0.762 miles 4,093 years=0.381 miles 2,046 years =0.190 miles 1,023 years =0.095 miles ( 503.54 feet) 512 years =251.77 feet 256 years =125.88 feet 128 years =62.94 feet 64 years =31.47 feet 32 years =15.73 feet Your point to point distance accounts for what time frame, under physical count. DwayneD.L.Rabon
Paleomagnetic data suggests that Vaalbara (the supposed supercontinent formed by the KapVAAL and PilBARA cratons) may not have existed- these cratons show at least a 30 degree rotation relative to each other- therefore not contiguous. South African Journal of Geology; December 1998; v. 101
The subsequent drift paths of the Kaapvaal and Pilbara cratons of 30 degrees taken at ca. 2.8 Ga gives further evidence that these cratons were formely connected much earlier at around ca. 31. Ga.
The subsequent drift paths of the Kaapvaal and Pilbara cratons of 30 degrees taken at ca. 2.8 Ga gives further evidence that these cratons were formely connected much earlier at around ca. 3.1 Ga.
Yes, this is what I am saying. I'm not saying that it is the correct view, but it is the consensus. The Earth first formed from gaseous/particle accretion and had a molten outer layer that froze over at ca. 4.5 Ga. As the iron and nickel percolated out and sank to the bottom to form the core, the radioactive decay and the heat generated from accretion melted the frozen-over outer layer. Hot spots, not mantle plumes, generated the first continental crust (correction to what I stated above, sorry). The author could not mean "plates" in the conventional sense as we know it: probably margins of continent crust.
So it is the residual heat of accretion and the radioactive decay that remelt the crust. The formation of the iron core is just something that occurs at the same time. Is that correct? Excuse me if I am sounding dumb, but I'd just like to be sure I am clear on what you are saying.
Ca. early 4.6-4.5 Ga was a period of heavy bombardment from asteroids and planetisimals. This era would not allow the earth to form a solid outer layer until accretion redistributed the elements. Then when it did, the earth's outer core solidified - froze over. Then, however, still at ca. 4.5, consensus has it that another planetisemal hit the earth and caused a large amount of the impact material to eject off and form the moon (different story). This impact itself would have released enough energy to remelt the early earth's still forming outer crust. Some time later, during the ensuing accretion process and formation of the inner core, the earth's outer crust would've started to form crust. We have zircon datings at 4.2 Ga in Greenland, Northwest Territories of Canada (Slave craton) and Western Australia. The earlieat rocks that remained intact from early continental crust are over 4.0 Ga from the Acasta gneiss of the Slave craton in the Northwest territories of Canada. There is a primary and secondary layer of crust that we recognize on Earth, Mars and Venus and our Moon, and a tertiary layer on Earth. 40 years ago we thought that the ocean crust was sunken continent. Now we know different. Ocean crust sinks because it consists of denser basalt. Continental crust rises 10's of kilometers higher because it is composed more of less dense granite. This is a reseult of early crustal formation. Radioactive decay and compression keeps the earth's iron-nickel core molten today and provides the heat energy responsible for the convection currents that circulate up through the lithosphere to continue the cycles of plate tectonic activity.
Kansas is part of the North American Shield which is itself the exposed sedimentary covered portion of the North American craton that formed from a conglomeration of former cratons. The North American Shield is the continental nucleus of North America and consists mostly of granitic and metamorphic rock, and a platform of sediments deposited on the outer part of the shield. Please Register or Log in to view the hidden image! "North America’s saga began over four billion years ago - fragments coalesced into microcontinents, which later collided to assemble the craton — the heart of North America. Plate tectonics has since enlarged this craton, and sediment has blanketed much of it, obscuring its eventful origins." http://www.mnh.si.edu/earth/text/4_1_3_1.html Actually, the portion of the craton that now includes Kansas was an addition to it that occurred 1.85-1.65 Ga and includes the portion that now consists of the landmass from Arizona to Missouria. Please Register or Log in to view the hidden image! Most of Kansas is the result of a Paleozoic uplift called the Arbuckle uplift and the subsequent Central Kansas Uplift during Pennsylvanian period (ca. 300 mya) strata that now directly overlie the Arbuckle strata, the basement rocks. Please Register or Log in to view the hidden image! Source: http://www.jamestown-ri.info/prelude.htm You can see from this map that Kansas was formed from the collision with the Yavapai Mazatzal craton ~1.8-1.6 Ga as part of the assembly of the North American craton. The gradual amalgamation of cratons formed the North America craton and most came from the original supercontinent Rodina, and the continent of Laurentia that was comprised of the Superior, Rae, Slave, Wyoming, Trans-Hudson, Wopmay, Yavapai, and Mazatzal cratons. After 1.8 billion years ago, most of the growth of the North American Shield, or more properly should be called the North American craton, occurred with the addition of Yavapai-Mazatzal, and Grenville and their corresponding orogenic belts, to the south and east of the Rockies. The Yavapai-Mazatzal craton was once connected to the Gawler Craton (now the North Australian craton) and its extensions in Antartica. The orogeny belts of these cratons were amalgamated into a 1.9-1.8 Ga margins of Gondwana during the Paleozoic. Proterozoic crustal assembly of the then Mazatzal “island arcs” with the then Yavapai proto–North American continent occurred at ~1.65 Ga. "Kansas doesn't have an active volcano, but lava did flow onto the surface as recently as 90 million years ago when dinosaurs still roamed the Earth." See: http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_kansas.html
Solid Iron/Nickel Rocks in Space As usual, Dr. Valich has excellent posts of information on his topic. The geology of mergings and splittings of cratons has been extensively researched over the past several decades, and much is now known regarding the 'plate tectonics' model of formation of our islands and continents as they currently exist. Where we disagree is in the earliest history of the Earth, for the time before which there is any geological evidence on the Earth's surface today, i.e. circa 4.6 to 4.1 Ga While the 'consensus' model of the formation of the Moon involves a 'glancing blow' of a huge asteroid striking the proto-Earth, as re-articulated by Dr. Valich., such model appears to be entirely unsupportable by physics. In particular, even if the proto-Earth were to survive such a 'glancing blow' as an intact body, the spray of iron-depleted mantle-ejecta into space (from which the iron-depleted Moon supposedly coalesced) would form millions (nay, billions) of asteroidal bodies that would rapidly cool into solid rock, all of which would obtain wild elliptical orbits about the remains of proto-Earth, if not actually ejected to escape velocity. Such spray of ejecta would eventually form a cloud of solid rocks in orbit about earth, quite similar to the cloud of solid rocks in orbit about the Sun which we call the Asteroid Belt. No plausible mechanism exists to have this spray-ejecta reform into a single body (the Moon), and even if such mechanism were to be 'constructed', the resultant body would be a solid, not a liquid. However, we know the Moon was once hot liquid, just as Earth is now almost entirely hot liquid (or hot-liquid compressed into a hot-solid-phase in the inner regions). We know this because of the extensive ancient basaltic flows on the moon. As mentioned in other posts on the topic, the Earth and Moon were almost certainly formed in tandem from the hot gaseous cloud of metallically enriched Hydrogen that was the precursor to our solar system, a portion of which was the precursor to our Earth-Moon system. An extensive model for the formation of the Earth and Moon in tandem exists, which results in the Moon being in orbit about the Earth in the plane of the ecliptic, in a nearly circular orbit, which is exactly what we observe. Likewise, the model also creates an enrichment of iron in the larger body (Earth) and a depletion of iron in the smaller (Moon). What the model does not yet detail is the next stage of Earth's genesis, i.e. the formation of the earliest cratons after the surface first cooled to below the melting point of rock, circa 4.5 Ga Perhaps the early history of the cratering of the Earth by asteroids has some impact on creation of such cratons. The decay of naturally occuring radioactive materials (which were much greater circa 4.6 Ga) would have been insufficient to account for the melting of a re-coalesced moon under the 'consensus' model, and is also insufficient to account for the melting of the Earth from solid rock, as is also postulated under the 'consensus' model. Likewise, collisional kinetic energies (of colliding asteroids/planetesimals) are also insufficient to melt solid rock, even if the added energy of radioactive decay were added in. Yet, we know that our solar system is filled with chunks of solid rock in wild orbits about the Sun. About 10% of that solid rock (about the same percentage as the Iron/Nickel core of the Earth compared to the less-dense Mantle) is in the form of solid Iron/Nickel, almost as pure as if straight from the foundery. Clearly, those chunks of Iron/Nickel in wild orbits about the sun are in fact the residue of a former molten planet, with an iron/nickel core, which was shattered. Likely the shattering process was indeed an impact with another large body; either a moon or large planet that was perturbed from its orbit by a nearby large body, such as Jupiter, and sent into an orbit that brought it into contact with that former planet, shattering it to smithereens, and sending small and medium chunks in wild orbits, cratering the inner planets (and Moon) extensively in the early history of our solar system. Those asteroids/meteorites we see nowadays are not 'leftovers' from the planet formation process that did not accrete into a planet, but are the residue of an asteroidal impact on a former planet, which does NOT form a Moon, but instead millions (nay billions) of tiny pieces sent into wild orbits which we call meteors/meteorites/asteroids. Walter L. Wagner (Dr.)
Not so, Dr. wagner. The resulting body would have coalesced into or from a solid, then after it became spherical and started to develop its own core of radioactive decaying matter (percolated out melt), would have then supplied the same source of heat as beginning proto-earth's, but since it was not as large of a quantity as earth's, it did not sustain that core as a liquid, as earth did. Dr. Wagner states: "What the model does not yet detail is the next stage of Earth's genesis, i.e. the formation of the earliest cratons after the surface first cooled to below the melting point of rock, circa 4.5 Ga Perhaps the early history of the cratering of the Earth by asteroids has some impact on creation of such cratons." As the earth coalesced from the accreted particles, we know that it first had a liquid magma outer layer. This outer layer then solidified BEFORE the formation of the inner core was in place. Once the inner core was firmly in place, through the percolated out iron and nickel that sunk to the center, the combined central unity of the radioactive decay of these elements then later remelted that outer layer, recirculating that solidified layer through hot spots into newly formed micro-continental crust and later oceanic arcs that contributed to the formation of the proto-supercontinents or proto-continents that we know to have existed. Plate tectonic activity, as we know it today, did not occur until some time after ~ca. 4.0 Ga.
What the 'H' is "combined central unity of the radioactive decay"? The amount of energy that would be released from radioactive decay would be the same no matter where the radioisotopes were located - all in the core region (e.g. dense U and TH sinking to the core), or spread throughout the entire planet. You clearly have not thought this out well. However, it does touch upon another topic I've discussed over the past decade, namely the possibility that a large body of Uranium/Thorium, concentrated in the core, might undergo some fission, adding energy not otherwise accounted for. However, this presupposes that the planet is alaready molten to allow for the U/Th to sink to the center of the core (U/TH is more than twice as dense as Iron).
I like this idea of yours. And it could have moved to the core if one of the prevailing theories regarding our moon is correct. If the moon was captured due to a major impact, a large portion of the Earth's core could have been molten for quite some time, allowing the same sort of distribution you would expect of a liquid in a centrifuge.
In case you haven't noticed, we do not have an asteroid belt near Earth. Why not? How can you explain why we only have this one large moon circulated around Earth while no other planets have nothing like it in comparison. Your theory calls for an asteroid belt near Earth. Just as the asteroid belt today has a largest asteroid (Ceres) at a 1000 km diameter, and several smaller bodies in the 300-500 km diameter range, the region of Earth's orbit would have had several bodies up to about half the size of the growing Earth, but in the case of Earth (but not any other planets) the impact happened late enough, and in such a direction relative to Earth's rotation, that abundant enough middle material was thrown out to make a moon. "Why this is a good hypothesis: 1. The Earth has a large iron core, but the moon does not. This is because Earth's iron had already drained into the core by the time the giant impact happened. Therefore, the debris blown out of both Earth and the impactor came from their iron-depleted, rocky mantles. The iron core of the impactor melted on impact and merged with the iron core of Earth, according to computer models. 2. Earth has a mean density of 5.5 grams/cubic centimeter, but the moon has a density of only 3.3 g/cc. The reason is the same, that the moon lacks iron. 3. The moon has exactly the same oxygen isotope composition as the Earth, whereas Mars rocks and meteorites from other parts of the solar system have different oxygen isotope compositions. This shows that the moon formed form material formed in Earth's neighborhood. 4. If a theory about lunar origin calls for an evolutionary process, it has a hard time explaining why other planets do not have similar moons. (Only Pluto has a moon that is an appreciable fraction of its own size.) Our giant impact hypothesis had the advantage of invoking a stochastic catastrophic event that might happen only to one or two planets out of nine." Source: http://www.psi.edu/projects/moon/moon.html
Dr. Valich: None of what you write 'rules out' the alternative theory I've previously discussed. Namely, that the Earth and Moon formed from a large gaseous cloud that started out essentially as a uniform mixture (hence the same isotope ratios on Earth as for the Moon), but it became a binary cloud (and about 1 in 3 proto-star clouds also become actual binary star systems [not failed binaries like our Sun-Jupiter system]) that subsequently became preferentially enriched in Iron and other heavier elements in the larger cloud. Nor does that model in any way require an 'asteroid belt' in the orbital range of Earth. Where do you get that from? Contrarily, there are significant difficulties with the collision model that is the 'general consensus' model. For example, it does not account for how the Moon ended up in an orbit that is in exactly the same plane as the orbit of the Earth about the Sun (plane of the ecliptic), when such colliding body would have had essentially no preference of direction for impact; My model essentially would require the two bodies to be in the same orbital plane. More compelling, perhaps, is that it does not provide any kind of valid 'mechanism' for creation of a moon from the 'residue' of such collision. Yes, it is tempting to assume that only iron-poor mantle material was ejected, giving rise to the moon. But no collisional process would create a large moon, even if leaving behind its iron-core to merge with Earth's iron core. In particular, a 'glancing collision' that did not shatter the earth would instead spew out a huge cloud of millions (nay, billions) of pieces of molten Earth, in nearly every direction, all of which would attain either wild elliptical orbits about Earth, or else attain escape velocity (circa 25,000 mph) and be lost from the earth-moon system. While we do know that such elliptical orbits would eventually circularize due to gravitational perturbations over time, this would take thousands to millions of years, far more time than necessary for each of the molten blobs to solidy into asteroids. Further, it would be virtually impossible for such a debris belt orbiting earth to coalesce into a moon, even a solid moon. While it might coalesece into several larger bodies, to have it coalesce into one large moon would take literally billions of years, yet we know the moon formed at about the same time as the Earth (from moon rocks, etc.) circa 4.6 Ga. And finally, there is no mechanism for it to re-melt (and we know it was once molten), as it would have been relatively depleted not only of Iron (in the core of Earth), but also of U-Th; and even if it weren't depleted of U-Th, the amount of heat released from that radioactive decay is insufficient over time to melt rock, since the U-Th is only about 0.0001% of the Earth. If we want to see the results of such an impact, we can look to the asteroid belt, with its millions of rocks in circularized orbits in a very wide band. Many of the asteroids are still in wild orbits, but not yet 'cleansed' from those inner orbits by having crashed into the Sun, Mars, Mercury, Venus, Moon and Earth. However, shortly after such collision billions of years ago, most of the resulting fragments were in wild elliptical oribts that took them eventually to crash into the Sun and inner planets, leaving behind only a small percentage (about 5% of a typical rocky planetary mass, by best estimates for the makeup of the asteroid belt) in relatively circular orbits (or mild ellipses) that eventually circularized over time. We know the asteroids (or, at least a goodly portion of them) are from a shattered planet, because there is no other plausible mechanism for the formation of iron/nickel meteorites other than shattering of an iron/nickel planetary core. You don't get relatively pure iron/nickel meteorites by any other mechanism. And we know they were once much more abundant. Some of the impact craters on Earth are now mined for Iron ore! So, the 'general consensus' model has essentially fatal flaws, and the model I have proposed can account for the features of our Earth-Moon system.
