Would Pangea cause an unstable wobble?

[Magnetic]

I was looking at an internet page which was describing the Pangea supercontinent and as I looked at it, I began to wonder if an unstable wobble would be present when all the land masses were on one side of the planet?

[nickolay1]

It would seem that the mass of the raised portion of the crust is rather insignificant.

[Sriad]

Yes, the portion of the Earth's crust which is higher than the center of mass of the crust as a whole would only be about 1/3, and the crust itself only represents about 2% of Earth's total mass.

Also, Earth has an unstable wobble now. We call it "seasons".

[Edi]

Also, Earth has an unstable wobble now. We call it "seasons".

That's not wobble. That's the axis of rotation staying constant as the earth moves around the sun. By wobble, I assume Magnetic is talking about changes in the planet's axial tilt due to an imbalance, which, as demonstrated, is not an issue.

Edi

[Gil Hamilton]

I've got a question, Magnetic? Do you post on another board where these questions come up and use this board as a resource to answer their points for you? Just curious.

[Lord of the Abyss]

I seem to remember an article years ago, that claimed that Mars was believed to have changed it's tilt due to a large buildup of solidified lava. The mass caused that region of the crust to be pulled to the equater.

The same article pointed out that Earth's Moon prevented anything like that here.

[GrandMasterTerwynn]

I seem to remember an article years ago, that claimed that Mars was believed to have changed it's tilt due to a large buildup of solidified lava. The mass caused that region of the crust to be pulled to the equater.

The same article pointed out that Earth's Moon prevented anything like that here.

It's more plate tectonics that saved Earth from a similar fate than anything else. The large buildup of solidified lava you're referring to is called the Tharsis bulge, and it plays host to the largest volcanoes in the solar system, i.e. Olympus Mons and its ilk. They formed over a hot spot in the Martian mantle, and never, ever meaningfully moved from that point. Compare this to Earth, whose very thin crust (The thickest continental crust is a mere 80 kilometers thick. The average thickness probably sits closer to around 20 to 30 kilometers) drifts over the mantle like so much arctic pack-ice. The movement is such that a volcano or complex of volcanoes couldn't sit on top of a hot spot long enough to form anything as remotely impressive as the Tharsis bulge.

[Magnetic]

I've got a question, Magnetic? Do you post on another board where these questions come up and use this board as a resource to answer their points for you? Just curious.

Sometimes this happens, but not in this case. However, IF I am on another board and matters of the scientific come up, I know that THIS board has many "overachievers" in that area of study, so to NOT come here for another view point would mean that I wasn't getting all the information that I can find. I hope that helps.

[Surlethe]

Magnetic, do a bit of your own research. Find out what an unstable wobble is; find out what causes unstable wobbles in spheres; find out the difference in crust depth between continental crust and oceanic crust; from that, discover how much "extra" mass would be lumped together in Pangaea; and finally, to tie it in with the first thing you found, figure out how much Pangaea would move the Earth's center of mass. That shouldn't be too terribly hard, now should it?

[CaptainChewbacca]

Pangaea may have caused a slight unstable wobble, but our planet has a large moon which greatly moderates the wobble. Mars has a severe wobble because it doesn't have a moon. An imbalance of mass wouldn't cause what happens to Mars, because over time it would "even out".

[Stark]

Chewie, what?

[CaptainChewbacca]

Chewie, what?

Sorry, I was tired when I wrote that, and it doesn't make sense. ANY planet which isn't a perfect sphere is going to have a wobble. Earth has two different "wobble" mechanisms, the first of which is the Chandler Wobble. This wobble is caused by deep-sea changes of salinity and temperature (I believe) and is something like .7 arc-seconds per year.

The second wobble of earth's is just called the precession of the earth's axis. That is a larger wobble of about 50 arc-seconds per year, which gives it a total of 360 degrees every 25,700 years. THAT wobble is caused by the gravitational forces of the sun and moon acting on the earth.

What I was trying to say is that Mars has a rather severe precession because it has no large moon to act as a second gravitational force on it. Continental/crustal mass distribution on a planet does not affect its precession in the long term because they happen over too long of a period to suddenly (geologically) affect the planet. Only in sea currents do you have sufficient mass and temperature changes happening quickly enough to affect change, and that is negligible compared to the natural gravitational influence of the sun and moon.

So, the answer to the OP is: No.

[Spin Echo]

It looks likes that Pangea may acutally cause the whole planet to tilt. I'm rather skeptical; I'm going to want to more evidence before I believe it.

link

North pole was once in Tahiti, geologists claim
Friday, 1 September 2006
Astrobiology Magazine

North pole was once in Tahiti, geologists claim
This graphic shows the tilting of the Earth that might occur if a dramatic imbalance in the planet's mass distribution ever developed in the Arctic. According to the theory of true polar wander, a heavy spot in the Arctic - caused by a very large upwelling of magma, for instance - would reorient the planet over 5 to 20 million years so that the heavy spot would lie at the equator.
Image: Maloof Laboratory

WASHINGTON, 1 September 2006: Imagine a shift in the Earth so profound that it could force our entire planet to spin on its side after a few million years, tilting so far that Antarctica would sit at the equator. U.S. researchers have provided the first compelling evidence that this kind of major shift may have happened in our world's distant past.

By analysing the magnetic composition of ancient sediments found in the remote Norwegian archipelago of Svalbard, Princeton University geoscientist Adam Maloof and his team have lent credence to a 140-year-old theory regarding the way the Earth might restore its own balance if an unequal distribution of weight ever developed in its interior or on its surface.

The theory, known as true polar wander, postulates that if an object of sufficient weight - such as a supersized volcano - ever formed far from the equator, the force of the planet's rotation would gradually pull the heavy object away from the axis the Earth spins around. If the volcanoes, land and other masses that exist within the spinning Earth ever became sufficiently imbalanced, the planet would tilt and rotate itself until this extra weight was relocated to a point along the equator.

"The sediments we have recovered from Norway offer the first good evidence that a true polar wander event happened about 800 million years ago," said Maloof. "If we can find good corroborating evidence from other parts of the world as well, we will have a very good idea that our planet is capable of this sort of dramatic change."

True polar wander is different from the more familiar idea of "continental drift," which is the gradual movement of individual continents relative to one another across the Earth's surface. Polar wander can tip the entire planet on its side at a rate of perhaps several metres per year, about 10 to 100 times as fast as the continents drift due to plate tectonics. Though the poles themselves would still point in the same direction with respect to the solar system, the process could conceivably shift entire continents from the tropics to the Arctic, or vice versa, within a relatively brief geological time span.

While the idea that the continents are slowly moving in relation to one another is a well-known concept, the less familiar theory of true polar wander has been around since the mid-19th century, several decades before continental drift was ever proposed. But when the continents were proven to be moving under the influence of plate tectonics in the 1960s, it explained so many dynamic processes in the Earth's surface that true polar wander became an obscure subject.

"Planetary scientists still talk about polar wander for other worlds, such as Mars, where a massive buildup of volcanic rock called Tharsis sits at the Martian equator," Maloof said. "But because Earth's surface is constantly changing as the continents move and ocean crustal plates slide over and under one another, it's more difficult to find evidence of our planet twisting hundreds of millions of years ago, as Mars likely did while it was still geologically active."

However, the sediments that the team studied in Svalbard may have provided just such long-sought evidence. It is well known that when rock particles are sinking to the ocean floor to form layers of new sediment, tiny magnetic grains within the particles align themselves with the magnetic lines of the Earth. Once this rock hardens, it becomes a reliable record of the direction the Earth's magnetic field was pointing at the time of the rock's formation. So, if a rock has been spun around by a dramatic geological event, its magnetic field will have an apparently anomalous orientation that geophysicists like those on Maloof's team seek to explain.

"We found just such anomalies in the Svalbard sediments," Maloof said. "We made every effort to find another reason for the anomalies, such as a rapid rotation of the individual crustal plate the islands rest upon, but none of the alternatives makes as much sense as a true polar wander event when taken in the context of geochemical and sea level data from the same rocks."

These findings, which are published in the U.S. journal theGeological Society of America Bulletin, could possibly explain odd changes in ocean chemistry that occurred about 800 million years ago. Other similar changes in the ocean have cropped up in ancient times, Maloof said, but at these other times scientists know that an ice age was to blame.

"Scientists have found no evidence for an ice age occurring 800 million years ago, and the change in the ocean at this juncture remains one of the great mysteries in the ancient history of our planet," he said. "But if all the continents were suddenly flipped around and their rivers began carrying water and nutrients into the tropics instead of the Arctic, for example, it could produce the mysterious geochemical changes science has been trying to explain."

Because the team obtained all its data from the islands of Svalbard, Maloof said their next priority would be to seek corroborating evidence within sediments of similar age from elsewhere on the planet. This is difficult, Maloof said, because most 800-million-year-old rocks have long since disappeared. Because the Earth's crustal plates slide under one another over time, they take most of geological history back into the planet's deep interior. However, Maloof said, a site his team has located in Australia looks promising.

"We cannot be certain of these findings until we find similar patterns in rock chemistry and magnetics on other continents," Maloof said. "Rocks of the same age are preserved in the Australian interior, so we'll be visiting the site over the next two years to look for additional evidence. If we find some, we'll be far more confident about this theory's validity."

Maloof said that true polar wander was most likely to occur when the Earth's landmasses were fused together to form a single supercontinent, something that has happened at least twice in the distant past. But he said we should not worry about the planet going through a major shift again any time soon.

"If a true polar wander event has occurred in our planet's history, it's likely been when the continents formed a single mass on one side of the Earth," he said. "We don't expect there to be another event in the foreseeable future, though. The Earth's surface is pretty well balanced today."