Gondwana supercontinent underwent massive shift during Cambrian explosion

Aug 10, 2010
The paleomagnetic record from the Amadeus Basin in Australia (marked by the star) indicate a large shift in some parts of the Gondwana supercontinent relative to the South Pole. Credit: Ross Mitchell/Yale University

The Gondwana supercontinent underwent a 60-degree rotation across Earth's surface during the Early Cambrian period, according to new evidence uncovered by a team of Yale University geologists. Gondwana made up the southern half of Pangaea, the giant supercontinent that constituted the Earth's landmass before it broke up into the separate continents we see today. The study, which appears in the August issue of the journal Geology, has implications for the environmental conditions that existed at a crucial period in Earth's evolutionary history called the Cambrian explosion, when most of the major groups of complex animals rapidly appeared.

The team studied the paleomagnetic record of the Amadeus Basin in central Australia, which was part of the Gondwana precursor supercontinent. Based on the directions of the ancient rock's magnetization, they discovered that the entire Gondwana landmass underwent a rapid 60-degree rotational shift, with some regions attaining a speed of at least 16 (+12/-8) cm/year, about 525 million years ago. By comparison, the fastest shifts we see today are at speeds of about four cm/year.

This was the first large-scale rotation that Gondwana underwent after forming, said Ross Mitchell, a Yale graduate student and author of the study. The shift could either be the result of plate tectonics (the individual motion of with respect to one another) or "true polar wander," in which the Earth's solid land mass (down to the liquid outer core almost 3,000 km deep) rotates together with respect to the planet's rotational axis, changing the location of the geographic poles, Mitchell said.

The debate about the role of true polar wander versus plate tectonics in defining the motions of Earth's continents has been going on in the scientific community for decades, as more and more evidence is gathered, Mitchell said.

In this case, Mitchell and his team suggest that the rates of Gondwana's motion exceed those of "normal" plate tectonics as derived from the record of the past few hundred million years. "If true polar wander caused the shift, that makes sense. If the shift was due to plate tectonics, we'd have to come up with some pretty novel explanations."

Whatever the cause, the massive shift had some major consequences. As a result of the rotation, the area that is now Brazil would have rapidly moved from close to the southern pole toward the tropics. Such large movements of landmass would have affected environmental factors such as carbon concentrations and ocean levels, Mitchell said.

"There were dramatic environmental changes taking place during the Early Cambrian, right at the same time as Gondwana was undergoing this massive shift," he said. "Apart from our understanding of and true polar wander, this could have had huge implications for the of animal life at that time."

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More information: DOI: 10.1130/G30910.1

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User comments : 14

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LariAnn
1.4 / 5 (10) Aug 10, 2010
Science fiction at it's best!
JeffJohnson17
1 / 5 (4) Aug 10, 2010
Well I guess the Government research Grantee's know best!
I found a dog bone in my back yard proving Aliens hate Bigfoot's 3 billion year old blanket.
malapropism
4.4 / 5 (7) Aug 10, 2010
Science fiction at it's best!

Why do you say that? You don't believe in (paleo)magnetism and geological science? Or are you perhaps a "young-earth creationist"?
thales
3 / 5 (6) Aug 10, 2010
Science fiction at it's best!


Not grammar at its best, though.
LariAnn
1.8 / 5 (5) Aug 10, 2010
I believe that science should consist of observed and observable facts, not speculation. Speculation is just that, speculation. Observations of paleomagnetism are facts, but jumping from 21st century observations to assertions that you now know what happened 525 million years ago is as much science fiction as Star Wars, maybe even more (IMHO). By the way, facts don't need to be believed in, they are to be known. Speculation is what requires belief. The word "science" is derived from the Latin word, "scientia", meaning knowledge. I rest my case.
malapropism
3.7 / 5 (3) Aug 10, 2010
Hmmm. Interesting reply. I'm not saying that you are necessarily wrong but until the invention of a time machine it seems to me that any conceptualisation of what may have happened in the past to cause some effect we see now, is likely to contain some speculative (or, perhaps more appropriately put, theoretical) element. On re-reading the article (I haven't gone back to the Journal) I don't think there was any "assertion" made by the researcher that doesn't seem fairly valid, at a cursory look at least, from empirical data (mean rate of plate movement, for example, current geomagnetic orientation in the rocks studied vs. earth's known magnetic field orientation at that point in the globe, etc).

BTW, Star Wars is fantasy really, not science fiction, and unfortunately it's not even terribly good fantasy. (I might get flamed over that one!) I take your point however.
malapropism
3.5 / 5 (2) Aug 10, 2010
Also, just to clarify, "science should consist of observed and observable facts, not speculation" - absolutely! (And theory based on them.) Not in any way suggesting otherwise... just taking some exception to your use of "science fiction" in describing the science of this article.
DamienS
4.4 / 5 (5) Aug 11, 2010
Also, just to clarify, "science should consist of observed and observable facts, not speculation" - absolutely!

Speculation is a very important part of the scientific process but it must be backed up with observational evidence if it's to be widely accepted. Even 'facts' are provisional.
Scott221
5 / 5 (2) Aug 11, 2010
I don't see any reason to call this researcher's work "speculation" rather than a genuine "hypothesis" (as at least one commenter has done). Granted, he seems to have found evidence of an unusually large shift in a continental land-mass that, so far as we know, cannot be explained very well by the well-established theory of plate tectonics. However, he does seem to be putting forth (what might very well be) the simplest possible explanation of this observed continental displacement - i.e. it may, in fact, be a "true polar wander" scenario that best fits the data. To dismiss that as speculation is inappropriate.
fmfbrestel
not rated yet Aug 11, 2010
Science fiction at it's best!


I thought the same thing until i read past the first paragraph. At first it seems like they are going to say that plate tectonics was the only explanation. But then, if you keep reading, you see that they offer the alternate explanation of polar wander.

It really is good practice to read the whole article and take everything in context.
Ronan
1 / 5 (2) Aug 11, 2010
Hm. I wonder, could a movement of the location of the magnetic north and south poles have some effect on this? I mean, rather than the entire surface of the Earth sliding over the inner portions of the planet en masse, might this have more to do with a shift of the magnetic field away from its previous orientation? I'm not saying that's more likely, mind, just wondering if the possibility (and IS it possible, by the way, for the orientation of the magnetic field to change that much?) has been considered.
Loodt
1 / 5 (1) Aug 11, 2010
Counter rotation anybody?

The plates moving in one direction and the centre core in another?

In the last 525 million years there must have been some cooling and the mantle thickened?

LariAnn, this field of study - paleomagnetics - is one of the most exciting in Geology today. It is a pity you that you dismissed it out of hand as new discoveries are made quite frequently.
fmfbrestel
not rated yet Aug 11, 2010
@Ronan -- Yes, and had you read more then the first paragraph, you would have realized that this possibility is discussed in the article.
Ronan
not rated yet Aug 11, 2010
@Ronan -- Yes, and had you read more then the first paragraph, you would have realized that this possibility is discussed in the article.

I think you may have misunderstood my post. I was talking about a change in the orientation of Earth's magnetic field. In the article, however, as far as I can tell that detail isn't touched on, but rather the question is whether Gondwana itself moved very rapidly while other plates stuck to a more staid velocity, or "...the Earth's solid land mass (down to the liquid outer core almost 3,000 km deep) (rotated) together with respect to the planet's rotational axis, changing the location of the geographic poles" Nowhere there is a mention made of a shift of Earth's magnetic poles, which is what I was speculating about. It's possible that I've missed something obvious in the article, but don't do me the injustice of thinking I didn't read it.