we all know that the natural tendancy of gravity is to spread mass equally over the face of a sphere. barring the existence of another super continent that has been completely subducted, what could account for such a large mass of land occupying only one half of the globe?

not to move this toward the realm of the pseudoscience section, but couldn't an explanation be a massive impact with another planet(oid) that obliterated one side of Earth? this event closely shadows the Sumerian creation story, metaphorically of course.

does anyone know of another, or for that matter the actual way Pangea came about?

well i believe plate tectonics would explain a lot. and actually there was a massive impact (or at least evidence of one) with another planetoid. That planetoid that smashed into the side of the earth is now the moon.

So, the oceans have no mass?

No, we do not know that "that the natural tendancy of gravity is to spread mass equally over the face of a sphere." Resistance? Equal mass? Counter forces? Coriolis effect? Centrifigul force? Magnetic resistance in rocks? Our magnetosphere?

Pangaea formed during the Permian about 300 mya.

Before that Pannotia formed about 600 mya and divided 50 million years after: Gondwana later then formed part of Pangaea.

Rodinia formed about 1,100 mya and divided about 750 mya.

Before this, I don't believe we know, but I may be wrong.

The Earth formed about 4.5 billion years ago, we have radioisotope evidence of rocks 4.3 bya, and fossil evidence of bacteria 3.83 bya in Northwest Australia.

well i believe plate tectonics would explain a lot. and actually there was a massive impact (or at least evidence of one) with another planetoid. That planetoid that smashed into the side of the earth is now the moon.Actually, the current theory is, as determined by minerals brought back from the moon, that the moon was created from outburst earth particles from the planetoid that impacted the earth: most of the moon consists of mass that came from the earth. It is thought that this caused the Earth's rotational tilt, and thus the seasons we have today.

So, the oceans have no mass?Spidergoat: Your being extremely facetious and senile. "Massive" means "large or widespread." "Mass" in physics means "a body of matter: a property of matter equal proportional to its weight."

I find it hard to believe that you didn't know what he meant.

Join the club.

Supercontinents may come and go in cycles:

http://gsa.confex.com/gsa/2004AM/finalprogram/abstract_75435.htm

That would have little relationship with the moon.

most of the moon consists of mass that came from the earth. It is thought that this caused the Earth's rotational tilt, and thus the seasons we have today.

I wonder who is thinking this, probably somebody with limited understanding of conservation laws.

I already posted above, the moon is made up of mostly the Earth's mantle mass because we know this from the minerals that have been retrieved from the moon. You can easily research this yourself on the internet but if you persist in denying it and demand further proof, I will supply it. But please take the time to act like a scientist and research it yourself first.

Supercontinents did not come and go in cycles in the beginning because they depended on too many variable and unknown factors when the earth was forming. The short "abstract" of the article you cited was very interesting but if you notice it only referrs to Pangaea 300 mya and on: no reference to their supposed h hypothetical "three billion years, in a process known as the supercontinent cycle." I think this is pure spectulation - no proof, no evidence. In any case, as I stated above, we have evidence of rocks - possibly a land mass - dating back to 4.3 bya.

All of this has absolutely nothing to do with "conservation laws," or whatever you are referring to? What do you mean by this? What Law?

Valich you are a hundred times more stubborn than your knowledge would allow you.

The short abstract of the article you cited only deals with continents formed after Pangaea 300 million years ago.

We are talking about the entire history of the Earth. That is 4.5 BILLION years.

This is a difference of 4.2 billion years that this article is not even considering, That's a 1500 times fold increase. Do you realize the astronomical difference involved here???

Explain yourself or do the research. This is a scientific forum community.

This is a scientific forum community.

Well it could have been if a certain somebody would stick to the rules a bit. It looks more like "I know everything and everybody has to listen".

Care to reread the first sentence of my link:

The Earth has witnessed the formation and breakup of five supercontinents over the past three billion years, in a process known as the supercontinent cycle

Your patronizing style without any patronizng capacities has caused considerable damage here in these forums as I can see.

Now, if you are so good, why not explain that the conservation of (angular and lateral) momentum could not have caused the tilt of the Earth axis during any collision with any celestial body.

I think we should just say God did it and go back to arguing about how many angels can fit on the head of my peni... pin. On the head of a pin.

:cool:

I have come across some studies that "suggest" that supercontinents are formed at approximately 250 million year intervals, but this is highly dubious and it is not supported by the facts:

Earth was formed about 4.57 billion years ago.
First known rocks were formed about 4.15 billion years ago.
First cratons were formed and mantle overturned about 2.8 billion years ago.

This mantle overturn is important because the circulation of the Earth's outer core is what drives the convection currents to overturn the mantle. This in turn is what causes tectonic plate movements in the upper lithosphere that cause continents to form. Before this time the Earth's surface was very unstable and consisted of a lot of volcanic activity.

Now here is where the facts do not support the 250 million year cycle:

The first known supercontinent "Columbia" existed between 1.8-1.5 bya. That's 300 million years.

The next known supercontinent, "Rodinia," (1bya-750mya) formed 500 million years later and existed about 300 million years.

However, the next known supercontinent, "Pannotia," (600-550mya) formed 150 million years later and only existed for 50 million years.

Finally Pangaea formed 150 million years later but only existed for about 20 to 30 million years before dividing up into Laurasia to the North and Gondwana to the South.

With the above facts in mind, I see no 250 million year cycle and think it is pure scientific hype with unsupported data. This is similar to the theory that glaciatian periods occur in 100,000 year cycles, yet this too is not supported by the facts:

Known periods of glaciations:
Huronian (2400 mya - 2100 mya)
Sturtian-Varangian (950 mya - 570 mya)
Andean-Saharan (450 mya - 420 mya)
Karoo (360 mya - 260 mya)
Cenozoic (30 mya - Present)

Source: http://en.wikipedia.org/wiki/Glaciation

Do you see a 100 my cycle here?
.................................................. .................................................. .
Also, Earth's continents are formed by plate tectonics, but the reason that we have a difference between land mass and ocean floor crust is because of the differences between the density of the rock (isostasy). Continental crust is less dense (mafic content) than ocean crust, therefore it stays above the ocean level.

Also, glaciers determine the weight pressing down on the continents. Solid ice above a continent will force it to sink below sea level. We are now in a warming trend since the last glaciation period and some of Earth's land masses are still rebounding upward, and will continue to rebound upward as more glaciers melt around the poles.

Also, as stated, plate tectonics that move the continents together or farther apart are caused by the molten outer core circulation. This circulation is caused by the Coriolis effect from the Earth's rotation. However, it is also influenced by the Earth's 23.5 degree axial tilt, the orbital change in that tilt (precession of the equinoxes - about every 25,000 years), the elliptical change in the Earth's orbit around the sun (eccentricity, or Milankovitch cycles), the Sun's different rotation patterns (magnetohydrodynamics), and the gravitational binding energy of the Earth that holds are entire atmosphere together.

"When there were large amounts of continental crust near the poles, the rock record shows unusually low sea levels during ice ages, because there was lots of polar land mass upon which snow and ice could accumulate. During times when the land masses clustered around the equator, ice ages had much less effect on sea level. However, over most of geologic time, long-term sea level has been higher than today....Sea level has varied by somewhat more than a hundred metres. This is primarily due to the growth and decay of ice sheets (mostly in the northern hemisphere) with water evaporated from the sea. The melting of the Greenland and Antarctica ice sheets would result in a sea level rise of approximately 80 meters."
Source: Wikipedia

"How did Pangaea come about?" Okay. I'm going to be brave and have a go at this, but I realize that I am opening myself up to criticism, and the criticism is very welcome and understandable. Also, I do not know how the diagrams will turn out when I post this, so even have to say to myself: "good luck."

In the beginning, you have to start with the formation of the first supercontinent Rodinia. Rodinia formed about 1 billion years ago and is thought to have embodied most or all of Earth's existing continental crust. It is thought to have broken up into eight continents around 750 million years ago, including the massive supercontinent called Gondwanaland (570-510 mya). The eight continents that made up Rodinia later re-assembled into another supercontinent called Pannotia and, after that, Pangaea.

Gondwanaland included what is now present day Africa, South America, India, Antarctica, Australia, New Guinea, New Zealand, the Gulf Coast of the United States, North America east of the Appalachians, the Marathon Mountains of West Texas, the Ozark and Smoky Mountains, and islands of the Caribbean). At this time Gondwanaland lay over the South Pole during a period of massive glaciation (sea levels dropped 50 meters – 160 feet). As it moved northward, it scraped clean the bottom of what is now the Pacific Ocean.

The continental cratons (large stable rock crusts of a continental plate) that formed Rodinia clustered around a central continent called Laurentia (the core of present day North America, and Ireland, Scotland, Greenland, and pieces of Norway and Russia). Laurentia then lay along the equator. To the east of Laurentia lay the smaller continent called Baltica (named for the Baltic Sea. It included present day Britain, Scandinavia, Eastern Russia, and Central Europe). Laurentia and Baltica collided about 416 mya and formed the continent called Laurussia (sometimes called Euramerica). Euramerica later became part of the major supercontinent Pangaea about 100 million year later.

http://www-sdt.univ-brest.fr/~jacdev/ens/images/pal04.gif
In this diagram you can see how Gondwanaland is over the South Pole, and how the Laurentia arc (here pointed out as Greenland) merged with the smaller continent called Baltica.
http://www-sdt.univ-brest.fr/~jacdev/ens/pal_brit05.htm

Gondwana then continued to move northward and collided with Euroamerica to form Pangaea between 340-275 mya.

http://www-sdt.univ-brest.fr/~jacdev/ens/images/pal08.gif

http://www.jamestown-ri.info/Pangaea.gif
Yellow = North America
Green = South America
Light blue = Africa
Red = Eurasia
Dark blue = Australia
Fuchsia = Antarctica
http://www.jamestown-ri.info/alleghenian.htm

Pangaea started to breakup about 40-50 million years later (~275 mya) into the continents we have today. Pangaea first rifted (split apart) into two continents: Gondwana and Laurasia (Euramerica was part of Laurasia). Laurasia later rifted into the two continents we know today as North America and Eurasia (Europe and Asia).

What was once called the continent Baltica, is now forming a new minor supercontinent Eurafrasia (Europe and Africa). About 250 million years from now, all continents will crash together forming a new supercontinent called Pangaea Ultima. About 400 million years from now, Pangaea Ultima will disintegrate, and no one knows what will happen from there.

Most of this information was compiled from: http://webspinners.com/dlblanc/tectonic/pangea.php http://en.wikipedia.org/wiki/Laurentia http://en.wikipedia.org/wiki/Baltica http://en.wikipedia.org/wiki/Devonian
http://www-sdt.univ-brest.fr/~jacdev/ens/pal_brit05.htm
http://www.jamestown-ri.info/Pangaea
http://www.devoniantimes.org/who/pages/euramerica.html

To the east of Laurentia lay the smaller continent called Baltica (named for the Baltic Sea. It included present day Britain, Scandinavia, Eastern Russia, and Central Europe). Laurentia and Baltica collided about 416 mya and formed the continent called Laurussia (sometimes called Euramerica).


Excellent summary, valich. One error: Baltica didn't include Scotland; just England, Wales and bits of Ireland. Scotland was part of Laurentia. The join between England and Scotland is the Iapetus Suture.

Jon

Spidergoat: Your being extremely facetious and senile. "Massive" means "large or widespread." "Mass" in physics means "a body of matter: a property of matter equal proportional to its weight."

I find it hard to believe that you didn't know what he meant.

Join the club.
I know what mass means. I was trying to point out the fallacy of thinking only land has mass. Actually, the oceans are very heavy. They press down on the crust underneath them with a tremendous force.

Vallich said:
First known rocks were formed about 4.15 billion years ago.

Would you mind 4.4 billion years?

http://science.nasa.gov/headlines/y2001/ast17jan_1.htm

Oldest known mineral: 4.4 billion years ago.
Oldest known rock: 4.15 billiion years ago.
http://en.wikipedia.org/wiki/Geologic_time_scale

Depends on how you want to define a rock?

In my post above, I did say that Scotland was part of Laurentia? Laurentia (the core of present day North America, and Ireland, Scotland, Greenland, and pieces of Norway and Russia). Laurentia then lay along the equator. To the east of Laurentia lay the smaller continent called Baltica (named for the Baltic Sea. It included present day United Kingdom, Scandinavia, Eastern Russia, and Central Europe).

Ocean crust is denser than coninental crust: that's why the ocean floor sinks down and continental crust rises above (mafic content). Water is not what exerts the tremendous downward pressure, but ice does. The continents on Earth are still rebounding from the last ice age and are expected to do so for the next 10,000 years. When Gondwanaland covered the South Pole, ocean levels dropped 50 meters and were covered with massive glaciers. You would thenk that if an entire continent covered an entire pole that the glaciers would melt and cause sea levels to rise, not drop. But since the land mass displaced the ice and underlying water in the South Pole, oceans levels dropped instead.