Explanations for Pangea

a while back i asked my college geology professor if the existence of Pangea could have been caused by a massive impact with another asteroid/planetoid, shearing one half of our planet away.

how else could all of that landmass exist on one side of a sphere?

he suggested that perhaps plate tectonics was a cyclical system. Pangea was the last time the prominent landmasses crashed together, in contrast to our present "spreading" pattern. eventually the Pacific will close and western America will crash into Asia.

can anyone shed any light on this discussion?

 

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Apart from your Professor is probably right, not much. Try googling for "Wilson Cycle". There have been a few supercontinents over the Earth's history. From wikipedia:

 

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makes sense.

 

How would Pangea been caused by an asteroid impact that broke the planet in half?

 

Well there have been vague ideas in the past that this astroid broke of a part of the world that became the moon, leaving the Pacific as a big scar, so when all the water gathered there, by default, the other side became a great continent.

But that was only an idea like millions of others.

 

We're all looking forward to the next time when the continents decide to split apart. I wonder where New Orleans will end up this next time around?

 

That makes no sense. The Pacific didn't exist when the Moon was formed. The outlines of the Pacific started forming roughly as the dinosaurs started dying out, when the continents were coming close to their present-day locations. And any scar left on the planet over four billion years ago would've "healed" due to erosion and continental shifting.

 

Our knowledge of geological formations date back hundreds of millions of years, while the age of the earth is an entire order of magnitude greater.

As Fraggle pointed out, random drift overtime and everything's bound to meet up.

 

Right and I didn't say that I endorsed the idea, did I? I just mentioned it.

Well at the end of the Mississippi, of course, which position has been accurately predicted by Mark Twain

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With the possibility that the continents will be drifting apart again in the very distant future, does that mean Topeka, Kansas will become a popular sea side tourist spot in about 100 million years?

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Well no, random drift is not exactly true because you have to start at the beginning of the accretion of chemicals that formed planets. Dust and gas particles collided that formed gravitational attractions. Planetisimal rocks collided to form proto-planets and then planets. The condensation, or accretion, of chemicals formed a molten Earth that eventually cooled to start forming a crust of solid rock. You cannot expect that this crust would instantaneously form around the entire Earth, instantanteously vanishing all molten rock, and it is much more probablistictic that it would have formed in one large clump and then split into peices, and here is where conjecture lies. A distance asteroid could have easily split a condensed solid land mass on Earth as this was a time when Earth was being bombarded with asteroids. Yet again, interior mantle circulations could have easily done the same! Hope this helps.

 

Well........I still maybe plan to buy some beach front property in Topeka, Kansas someday, regardless of the prospects. I guess I'll know if it was worth the investment in about 100 million years or so. Right?

 

To answer the question, Pangea was not caused by an asteroid/planetoid impact.

As was stated above, the Earth's mantle works by a cyclic two-layer convection system that has brought together continents and seperated them at various times throughout Earth's history (plate tectonics). The most famous supercontinent is Pangea that formed when smaller continents aggregated together about 290 million years ago and then broke apart into Laurasia an Gondwana about 200 million years ago, but their were many other supercontinents that existed before this. For example we now know that there was a very early Archaen supercontinent that formed around 3.6 billion years ago called Vaalbara made up from cratons (the Pilbara cratons) - smaller than most present-day continents. Evidence of this is in the present-day Yilgarn Craton that makes up Western Australia. There was also another supercontinent 2.42 billion years ago called Kenorland that was formed by the Kola and Karelia cratons (present-day provinces in Russia). Six or seven cratons formed the Canadian Shield 2.0-1.8 billion years ago. There were also the Columbia supercontinent (1.8-1.5 bya) and then the Rodinia supercontinent (1.1 bya - 750 mya) that formed around one billion years ago. Most of these supercontinents were relatively short-lived, so I don't think there's any need to buy real estate in Topeka.

The geology behind all this is extremely fascinating. We can assume that early Earth did not have a plate tectonic system because it was formed by the accretion of smaller planetisimals and then condensed into layers. The low-temperature melting rocks, such as iron and nickel, sank to the bottom to form the Earth's inner core leaving the lighter silicates in the upper mantle. At first the entire surface of the Earth would have had to be molten magma that eventually froze over as these heavier elements percolated downward. The entire surface of the Earth would've been a very thin solid landmass (a thin, rigid lithosphere). The core, however, remained extremely hot - and still is from radioactive decay - and this then would've started the cyclic convection system that led to plate tectonics. The Earth would then have first formed a very shallow ocean and volcanic activity would have begun to create land masses. Early crustal deposits generally all contain a high basalt magma content (igneous rock) with little sedimentary rock.

If you're interested in this, do a search on Archean supercontinents or Archean paleogeodynamics.

"The active tectonics of the Archean produced numerous, relatively small continental landmasses that were very mobile as they floated on the turbulent mantle. Toward the end of the Archean, however, these minicontinents had begun to coalesce. By about 2.5 billion years ago when the Archean eon came to an end a more tectonically stable supercontinent had formed from the accreted landmasses. About 70% of modern continents are Archean in age and were derived from this single large landmass. This supercontinent had a much thicker crust than the earlier, smaller crusts and heat flow from the mantle had begun to subside. As a result volcanic and tectonic activity within and along the margins of the supercontinent, were reduced significantly by the start of the Proterozoic." http://www.bookrags.com/sciences/earthscience/archean-woes-01.html

For a possible explanation of the breakup of the Archean supercontinents by magma plumes see: http://www.lithosphere.info/Drag-2002.html

On the earliest Archean supercontinent Vaalbara see: Tanja Zegers et al., "Vaalbara, Earth’s oldest assembled continent? A combined structural, geochronological and paleomagnetic test." Terra Nova 10, 250-259

On the 3.475 billion year old Komatii Formation and the above cited Paleomagnetic Archean Supercontinent Project, and the Greenstone Belts of Vaalbara, Gondwana and Laurasia, with excellents maps and diagrams: http://web.uct.ac.za/depts/cigces/gsbelts.htm

 

Valich:

As usual, you have excellent references.

Alas, I believe your earliest presumption is likely in error. If you check my other posts, you will see that many (or, at least a few) theorists now believe that Earth was formed by the condensation of a large, hot Hydrgogen cloud, with a miniscule (circa 0.1%) admixture of heavier elements isotopically thoroughly mixed throughout the gas (as it was separated from an even larger cloud that was also isotopically thoroughly mixed, which gave rise to the Sun and the other planets).

As the gas cloud (proto-Earth) slowly collapsed and released radiant energy, eventually the pressure produced the boiling point of elements and compounds, and a rain-out of those materials commenced, with iron, nickel, oxides, etc. forming a rain towards the center of the cloud, according to their relative boiling points, with gravitational stratification causing the denser materials to sink towards the center.

Later, nearby OB stars in the stellar nursery that gave rise to our Sun and numerous other stars (much like we see taking place in other parts of our Galaxy), with their high UV output, volatilized away the Hydrogen blanket, driven away by the solar wind, leaving behind the molten inner core (and also true for Mercury, Venus, the Moon, Mars, and the moons of the 'gas giants' that still remained), which then solidifed a crust, leading to the stages that you thereafter describe. Even the 'gas giants' (Jupiter, etc.) lost much of their Hydrogen under this theory, but not all, likely because they were larger and/or far enough away from the solar wind to not lose all of their Hydrogen blankets.

The collisions of planetisimals, the leading other theory now being attacked by numerous theorists, does not allow for sufficient heat to melt the planetismals (a recent Scientific American article shows only a tiny amount of melt with each collision, and then it radiates away and solidifies between collisions), and likewise radioactive decay of presumed elements to be then existent also does not adequately account for the necessary heat to melt Earth, even if combined with collisional energies. That has been the big stumbling block of the prevalent theory, as well as many other factors (such as why the moon orbits in the same plane as the Earth's orbit about the sun, etc.).

Anyway, check some of my recent posts and you'll learn more about this newer theory of Earth's earliest history.

Regards,


Walter

 

Hey Walter!

Glad to hear from you again. I thought you might have been engulfed by one of those Hawaiian volcanoes?

I do admit that my first post was in error on the second half, but I don't think that proto-Earth was a "gas cloud": it was an an accretrion of planetisimals that then condensed. gas clouds could not contain the heavier elements of iron, nickel, and sulfur? The subsequent condensation then produced the iron core as we know it.

This is your first posting on this thread so what other postings are you referring to? Please site your sources as they benefit us all, right?

 

Valich:

It took me a while to figure it out, too. The old planetisimals colliding theory was well-ingrained. Here's how to visualize it:

One or more supernovae in the vicinity of a very large cold cloud of primordial Hydrogen (and Helium, which I'll ignore hereafter) in our galaxy shot a very hot 'jet' of gas at that cloud.

We know that supernovae produce a whole range of isotopes/elements (peaking at Iron, but by rapid neutron capture, going up to Plutonium and beyond, and these are injected into nearby Hydrogen clouds. Astrophysicists routinely talk about the "metallicity" of gas clouds and proto-stars, to determine how many supernovae might have been going off in that region, enriching the clouds.

The supernova ejecta are all monatomic elements, very hot (high speed) and would be circa 1,000,000 degrees C relative to a nearby cold cloud.

If such jet(s) were to strike a nearby cold cloud off-center, two things would happen:

1. If the 'jet' (perhaps nearly half of the total supernova, the other half going away from the cloud) had a total mass of Iron, Aluminum, Oxygen, Carbon, Uranium, etc. monatomic atoms in it that was roughly 0.1% the mass of the cold Hydrogen cloud it struck and got mixed into, the overall temperature of the resulting mixture would be roughly 1,000 fold lower than the original hot jet, and hence the original cold cloud of Hydrogen would now be a warm cloud of Hydrogen, with an admixture of gaseous Iron, etc. (the 0.1% admixture of other elements), warmed to about 1,000 degrees C by the ejecta;

2. The cloud, being struck off-center by such a large mass, would begin slowly spinning as the hot jet got thoroughly mixed, and eventually all of the admixture elements would have all of their respective isotopes thoroughly mixed in the Hydrogen (over the course of millions of years) which would create a slowly spinning Hydrogen cloud now ripe for solar system formation along the lines of our solar system.

Most of the cloud would slowly contract and form a central mass (proto-star), but a significant percentage would form bands of gas in orbit about the proto-star. We routinely see similar things in nearby stellar formation in stellar nurseries, in which the protostars are surrounded by a disc of gas.

Eventually, the bands of gas in orbit about the central proto-star would coalesce/condense into separate balls of gas going in orbit about the proto-star, and thereafter, the rain-out would commence in each respective ball as it gravitationally collapsed, forming molten central bodies such as believed to exist in Jupiter, etc. [If the ball of gas was small enough, there might well be a snow-out instead of a rain-out, forming carbonaceous-chondritic type materials, rather than molten materials such as basaltic/magmatic or iron-nickel type materials.]

This is actually what one would naturally expect for virtually any solar system formation from Hydrogen clouds, and what I predicted in 1996, before we began discovering large gas-giant planets in Earth-orbit ranges a few years later, which discoveries were contrary to then-existing theory, but exactly in agreement with my predictions.

We also see in nearby stellar nurseries that many stars form essentially nearly simulatneously (relative to the life-times of the stars) in very large gaseous clouds, and they are obscured initially by the large amounts of gas and 'dust' in the clouds, but eventually they 'push away' or erode the obscuring features of the clouds, revealing the newly formed stars in the 'stellar nursery'

Simply using that same type of process of many nearby young stars in the Earth's early history 'eroding' the gas remnants of the original cloud, as well as the much more loosely gravitationally bound Hydrogen around the protoplanets would leave many such gas-giants being eroded to their bare cores, including Earth, etc. That is a process that is believed to take only a few tens of millions of years.

Eventually, once all of the remnants of the original gas cloud was blown away by the stars' solar winds, they would be able to 'drift' away from each other by their owh inherent motions, no longer gravitationally bound by the mass of the original super cloud in which they were born.

These gas clouds are everywhere in our Milky Way. Astrophysicists measure their speeds in terms of mach, and they typically are moving at around Mach 5 to Mach 15, relative to other nearby clouds. If they collide, they can and do form stars.

We really see these collisions a lot when galaxies collide. They routinely produce lots of stars at their regions of intersections, and by training telescopes to the tell-tale frequences of new-star light, many such colliding galaxies have been detected.

This theory also works well to explain the Earth-Moon system, and its different Iron ratios. As you know, the Earth is much richer in Iron than is the Moon. A large body striking the Earth, and ejecting the mantle material to form the moon, is a poor explanation, particularly with how the Moon just happened to be ejected almost exactly into the same plane as the orbit of the Earth. Quite a coincidence.

Alternatively, if the Earth-Moon system started as a large band of gas that coalesced into a spherical cloud that happened to have two gravitational centers (which is quite plausible, considering how many binary stars we see), initially the Iron atoms would have spent more time around the larger gravitational center, and would preferentially enrich that region, compared to the smaller gravitational center. Eventually, the cloud would continue to condense until it became two separate clouds in orbit about each other, and the gaseous components (Hydrogen, Iron, etc.) would no longer be in communication, and two separate rain-outs would thereafter take place, with the moon having very much smaller a percentage of iron in its rain-out material, thus producing mostly mantle material and only a very tiny iron core, compared to the Earth.

Anyway, I hope you were able to follow this.

Remember, because the cloud is warm, all of the elements are monatomic, including the Iron, Gold, Uranium, etc., and in gaseous form, even the iron, etc., and the clouds would simply follow the laws for gasses.

Regards,



Walter

 

You'll have to check my posts by clicking on all of the posts I've made. Sorry. They've been in many threads over the past two months. I'm only at 100+ posts, so it would not be too difficult

 

It's a tantalizing theory that I have to think about, and it does go beyond my realm. Can you PLEASE post some sources that support this view? In no way am I disclaiming it, but scientific sources normally start off with an abstract or summary, then review the peer-reviewed artiles to date, then go into their study or experiment, then their results and conclusion. This would be a tremendous help for me as an introduction to your hypothesis, as I alluded to above. Why are you not cited any sources???

 

Lets take the analogy of waterdroplets. They seem to cling together. Drifting on magma, bigger pieces of landmass sticked together.