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Tokyodreamer
SFN Regular
USA
1447 Posts |
 Posted - 06/05/2001 : 11:26:52
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This is something I've always wondered about, but can't seem to find an explanation after a cursory search.
Apparently, it is widely held that at one time, all the continents were connected in one big mass called Pangea. My question is, what on earth caused all the land to be together in one mass, instead of just randomly dotting the surface? Take a ball of clay, and squeeze up one lump in one section, and you'll visualize what I mean (I hope). Is there a geological reason for this?
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Gambatte kudasai!
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@tomic
Administrator
USA
4607 Posts |
 Posted - 06/05/2001 : 11:43:11 [Permalink]
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I have wondered the same thing myself.
@tomic
Gravity, not just a good idea...it's the law! |
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Lisa
SFN Regular
USA
1223 Posts |
Posted - 06/05/2001 : 12:04:00 [Permalink]
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Dang, when I took geology, I can't recall that one ever being answered. I wonder if Pangea was really the first? Or if the continents have been slamming into one another since this mudball was formed. BTW, did you know that in the last century, we've move 1/4 inch further away from Europe? Guess that explains air fare.
I wish I still had my "Reunite Pangea!" T-shirt.
Lisa
Chaos...Confusion...Destruction...My Work Here Is Done |
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Tokyodreamer
SFN Regular
USA
1447 Posts |
Posted - 06/05/2001 : 13:00:12 [Permalink]
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yes, I was wondering if the continents that happened to be above the sea level maybe started out at a random placement, and some force caused them to drift together. But if that were the case, they shouldn't have broken apart since! I need to find a geologist's email address...
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Gambatte kudasai! |
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Tokyodreamer
SFN Regular
USA
1447 Posts |
Posted - 06/05/2001 : 13:01:08 [Permalink]
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Oh wait, I just thought of the answer!!!
God made it that way! 
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Gambatte kudasai! |
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Bozola
Skeptic Friend
USA
166 Posts |
Posted - 06/05/2001 : 13:38:09 [Permalink]
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1. Plate Tectonics. Summary: The continents are drifting around on the mantle of the Earth.
2. Pangea is thought to exists by the application of the theory of continental drift to the findings of similar mineral and fossils in different places. Think of it as an enormous jigsaw puzzle with a lot of pieces missing.
No, Pangea was not the first continent. It really wasn't that long ago that it existed in the Earth's history, just a scant 250 million years. It's just about as far back as we can reasonablely see the overall tectonic history of the planet. The further you go back in time, the more that pieces get lost in your jigsaw puzzle, and the resolution gets really bad.
Bozola
- Practicing skeet for the Rapture.
Edited by - Bozola on 06/05/2001 13:44:32 |
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Tokyodreamer
SFN Regular
USA
1447 Posts |
Posted - 06/05/2001 : 15:09:47 [Permalink]
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I know about continental drift, but I thought it was relatively random. What I meant was some force directing the drift so that the land masses merged together.
From what I remember from middle school science class, Pangea was one big continent, all by itself, and the rest of the world was ocean. My question was, what caused that one big mass to be above sea level, and/or what kept other land masses from being above sea level at that time?
Are you saying that when Pangea was around, there were other continents around also? That would make sense. And the other continents just aren't related to our current geographic makeup.
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Gambatte kudasai! |
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Bozola
Skeptic Friend
USA
166 Posts |
Posted - 06/05/2001 : 16:05:01 [Permalink]
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Random? Chaotic and complex, I think is closer to reality. I like to think of continents akin to scum on the surface of a slow cooking soup. There's some mighty strong convection currents dictating the motions.
We like to think of granites (the building stuff of cratons) as heavy stuff, but really you should think of them as icebergs floating on the Mantle. 40km deep icebergs.
Cratons (the stable cores of the continents)
don't relly ever 'merge'. Nor do they subduct. They just sort of bump into each other then eventually move on (a gross oversimplification, I know). Pangea was made up of a bunch of these craton; think of it as a quilt.
The motion that brought all of the continents together to form Pangea eventually broke it apart. This motion is still happening, and it is still readily visible in the Rift valley in Africa, Southern California, and the Indian subcontinent.
quote:
My question was, what caused that one big mass to be above sea level, and/or what kept other land masses from being above sea level at that time?
Parts of it probably did have shallow seas at various points in time. That the illustrations show no seas, I think reflects more on the sparcity of data than anything else. The middle of North America was an ocean bottom back in the Cretaceous, after all (But, you've got to remember that the edges of the continents are generally the lowest spots, and water always flows downhill).
Bozola
- Practicing skeet for the Rapture.
(i cannot spell)
Edited by - Bozola on 06/05/2001 16:07:14 |
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Rift
Skeptic Friend
USA
333 Posts |
Posted - 06/05/2001 : 16:50:01 [Permalink]
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The other thing is Pangea might not have been the only contient at the time, Just the only one that has had pieces survive to today.
Like Boz said, the further back you go the less and less we can reliably be certain.
And again like Boz said, it's not totally random.
There's still a lot we don't know... I remember seing a show about the san fransisco area where they thought that there are remenants of about 7 or 8 plates in the area, slowly being sucked under the north american plate...
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James
SFN Regular
USA
754 Posts |
Posted - 06/05/2001 : 20:32:37 [Permalink]
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Well, actually, it's called subduction and it's more like the plates are being pushed down, down into the mantel, really being turned into a liquid form(magma) due to the great pressures and temperatures at that depth.
For an example of how this works, try this:
Take your two hands and lay them out flat, with the middle fingers touching. Now, have one hand gently slide over the other. The one that is one top is, let's say, the North American Plate on the West Coast. The hand(plate) that is going under can be either the Juan de Fuca Plate in the Northwest, the Pacific Plate or a couple other plates that I forget the names of right now. In fact, this same process is happening all over the world and a very good example of this would be over around Japan. Japan literally sits on like, I think, five plates.
On Pangea:
Way back when everything was all together, there probably were many continents everywhere. But, as we all know, everything moved around to today's positions about in the Cretaceous period. When Pangea began to break up, the Atlantic was formed. And it grew into the Atlantic we all know and love today. Eventually, we will no longer have a Pacific Ocean. Probably take a few million to a few hundred million years, but it will happen. And the mountains that will form will make Mount Everest(formed by India smashing into Asia) seem like an anthill. At least, that's just a guess. Oh, and Asia and North America will join up again up at Alaska and the Chukchi Penninsula.
Edited by - James on 06/05/2001 20:45:01 |
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Bozola
Skeptic Friend
USA
166 Posts |
Posted - 06/05/2001 : 21:29:56 [Permalink]
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quote:
Well, actually, it's called subduction and it's more like the plates are being pushed down, down into the mantel, really being turned into a liquid form(magma) due to the great pressures and temperatures at that depth.
Yep, but it's important to note that these plates are composed of heavier seafloor basalts that are shoved down as they abut up against the continents. When they get deep enough, the basalt melts which then slowly begins to rise. This is what powers the coastal volcanos of the "Ring of Fire". This basalt material, being oceanic in origin, is also high in water content. This make these volcanos much more explosive than other volcanos. All of the super-heated steam. Compare Mt. St. Helens to Kilauea.
of other note:
As the plate subducts, seafloor sediments are scraped off and build up at the edge of the subduction zone. In Washington, these scaped-off sediments are called the Olympic Mountains. Much of the sedimentry rock has been miked soo much, looks like a dark, striped taffy. Remnants of these formations can be found in the Kootenay valley (where the Okanagon microplate meets the North American) and the Okanogan valley (where the North Cascades microplate meets the Okanogon).
When the Juan de Fuca plate finally finishes subducting, the Cascades volcanos will cease their growth.
Bozola
- Practicing skeet for the Rapture. |
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Trish
SFN Addict
USA
2102 Posts |
Posted - 06/05/2001 : 22:16:25 [Permalink]
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Let's see if I can remember my geology classes from college, LOL! Also, in addition to the subduction on the pacific rim, the atlantic rift valley is a line of volcanoes acting to push the N & S American plates and the European plates farther apart. Hence, assisting the subduction on the Pacific Rim. Oh well, the kid took my geology book again...They actually have a better explanation of this process in there. I'll find it tomorrow!
He's YOUR god, they're YOUR rules, YOU burn in hell! |
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Zandermann
Skeptic Friend
USA
431 Posts |
Posted - 06/05/2001 : 22:25:34 [Permalink]
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quote:
... Oh well, the kid took my geology book again...They actually have a better explanation of this process in there. I'll find it tomorrow!
ahhhh...I hope tomorrow's not too late!! Those plates are moving at a terrific rate!
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James
SFN Regular
USA
754 Posts |
Posted - 06/05/2001 : 23:03:33 [Permalink]
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quote:
Also, in addition to the subduction on the pacific rim, the atlantic rift valley is a line of volcanoes acting to push the N & S American plates and the European plates farther apart.
Don't forget the African Plate. Why do you think the eastern coast of South America and the southwestern coast of Africa look like they do?
"Try not. Do or do not. There is no try." -Master Yoda |
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Trish
SFN Addict
USA
2102 Posts |
Posted - 06/05/2001 : 23:24:09 [Permalink]
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quote:
Don't forget the African Plate. Why do you think the eastern coast of South America and the southwestern coast of Africa look like they do?
Yes I know...but this is stuff I haven't covered in six years! The book names all the plates and discusses their individual movements based on current understanding (from six maybe seven years ago). It also covers how an individual plate movements affects the other plates.
He's YOUR god, they're YOUR rules, YOU burn in hell! |
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Tokyodreamer
SFN Regular
USA
1447 Posts |
Posted - 06/06/2001 : 08:40:51 [Permalink]
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quote:
Random? Chaotic and complex, I think is closer to reality.
Thus the 'relatively' qualifier. I was trying to avoid all the unnecessary detail about drift, tectonics, etc. (not that I don't appreciate your info, I just already know about it  ) I was just wondering about the way Pangea was taught in school. The world is covered completely with water, except for this one big lone landmass. So either the model they teach is wrong, or some weird cosmic coincidence caused all the land above sea level to join in one lone mass, or some force acted on all the plates, and pushed them together, leaving none of them on their own.
Imagine a bunch of boats floating on the water. Left on their own, for some reason they all drift together and bump into one another, with no boat left on it's own. Some force (current, wind, magnetism, gravity, pressure, you know what I mean) caused the boats to come together in one big mass, instead of floating off seperately, or forming multiple smaller masses of boats. Why did they all come together in one big mass?
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Gambatte kudasai!
Edited by - tokyodreamer on 06/06/2001 08:42:13 |
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