Talk:Supercontinent cycle

Why oscillation instead of steady-state equilibrium ?

That is, why doesn't rifting happen concurrently with collisions to keep the number of continents relatively stable ? Instead it seems like rifting must stop, or at least reduce dramatically, during the collision process and vice-versa to get the oscillation between a single super-continent and many separate continents. Why would this be ? StuRat 21:00, 13 May 2006 (UTC)

Attempt to amplify the above

Which is cause and which effect? If you consider the continents to be at any given time floating like pucks on an air-hockey table - in extreme slow motion - then once they move they keep on going until stopped. This presupposes a lateral acceleration to get them moving, the build-up of sufficient momentum to keep them going against resistance from tectonic activity, and a purely mechanical consideration of energy absorption during collisions. These collisions may therefore spark one of absorption of the crust (subduction), folding (collision), or "bouncing" (the continents may strike a glancing blow and further motion may be reversed or rotation may take over, like two air hockey pucks hitting each other).

If you keep on going in this reasoning there seems to be little reason why a supercontinent would split in the first place. Although it seems that the continental crust may be weakened by thermal effects, if it splits in the middle of the continent you would need an enormous push to get things moving as the supercontinent must be well anchored and have maximum inertia. One might expect that a volcanic ridge would form and "overflow" rather than actually create tectonic plates, or that volcanic action would be confined in perpetuity to the plate edges. Once in motion, however, the parts of that supercontinent would, in the absence of other forces, move around the globe and then meet up again in a different configuration. The "other forces" are what complicates matters.

The original energy available in the original rifting is not known; nor are the stiffnesses of the rocks around where it occurred (we always work backwards in time, stating that rifting seems to have occurred here and there). It also seems to be directional, discontinuous and unstable (look at what seems to have happened to Africa, Antarctica and Australia during their split from Pangaea - India hurries north, Australia flies west, Antarctica shuffles south, and Africa moves a little north, while Madagascar moves in the opposite direction (or possibly stays where it was, but that is a private opinion). In addition, one cannot assume that these events are not counteracted elsewhere - the passage of a continent must cause ructions along all its edges, and this around the globe, so one rifting may influence another. If a plate moves say east, will it produce rifting along its western edge, and will this act as an "outboard motor" to keep it accelerating? Furthermore, the whole earth is in motion, spinning on its axis, with gravitational forces involved that can also influence the dispersion of crustal plates. It is a many-body problem with far too many factors involved for more than top-level analysis by myself as a layman.

Jeremynicholas 13:39, 22 August 2006 (UTC)

I'm really a layman too, but I can imagine a possible reason why a supercontinent, once formed, would split up again. It may have to do with the fact that continental crust is much higher and less dense than oceanic crust, leading to a higher degree of insulation. So, once a large portion of the earth's continental crust is collected in one hemisphere, I would expect the build-up of an ever so minute differential in temperature in the lower layers.

This differential would over long periods of time cause a restructuring of currents in the mantle, leading to increased activity with its epicentre in the most landlocked parts of the supercontinent. And I mean "long periods" in geological time - somewhere in the order of 10^8 years. These mantle-internal processes must indeed be much slower than the continental drift itself, else we would not expect continents to ever collide and form new supercontinents, as the temperature differential starts to build up as soon as the plates only approach each other. If we look at present-day active rifts, the predictions seem to be largely correct: Africa is in the process of splitting up at the Mbéré Rift Valley and the Great Rift Valley - and it was the most continental part of Pangea, though not extraordinary in this respect nowadays. So, that would give us an approximate time-scale: The major tendencies in the mantle Pangea caused are still active today.

To make an analogue: Imagine a water basin with a heat source at the ground, just about to weak to keep the water boiling. Now put in a some boards of foamed polystyrene close to each other. The water will start boiling underneath them, and only there, driving them apart.

I don't know whether something along the lines of what I suggested is part of geological theory, and if not, what are the counterarguments - but it seems to work. A layman, 213.47.123.225 16:18, 2 April 2007 (UTC)

According to The Rough Guide to Climate Change (p.211), average plate speeds today are two-thirds of what they were 100Ma. According to the Open University textbook Mountain Building (p.11), the subcontinent India today is moving at about one-third of what it was 50Ma (15cm/year → 5cm/year). Ipso facto, when continents collide, and uplift mountains (Orogeny), collision coincides with deceleration of tectonic plates. Inexpertly, slower plate speeds imply less geo-volcanic activity, at spreading ridges, and subduction zones. So, geo-genic Carbon Dioxide would plausibly track average plate speed — Carbon Dioxide levels would tend to be high, when plates were moving geologically quickly, et vice versa. And so, the assembly of supercontinents, associated with massive mountain making, would plausibly tend to co-occur, with reduced atmospheric CO₂ levels, and global ice-house conditions, even Snowball Earth periods. 600Ma, a supercontinent existed, as earth underwent global glaciation; 300Ma, Pangea existed, as did polar icecaps and colder climates. Average plate speeds, atmospheric CO₂, global temperature, and supercontinents, all seem related.66.235.38.214 (talk) 19:14, 27 October 2012 (UTC)

4000 million years

I'm assuming that the author is using "4000 million years" to mean 4,000,000,000 years out of respect to the old British usage of million and billion. Most English speakers, including in the British Isles, now understand 4,000,000,000 to mean 4 billion, so I'm going to make that change. If there are a large number of people out there who feel that this would be confusing, we'll have to figure out another solution.

Farside268 00:11, 26 November 2006 (UTC)

Why change it as in that form it is unambiguous? No-one can be confused by 4000 million. Also, it has some consistancy as the article otherwise deals in hundreds of millions of years, and therefore the relationship between hundreds of millions and thousands of millions of years may be clearer than between hundreds of millions and billions. —Preceding unsigned comment added by 82.32.72.129 (talk) 23:09, 2 April 2010 (UTC)

There is a far bigger problem than this one number. There is a section in 100s of millions, a section in billions and a sections in Ga. This makes the article more difficult to read. Given that this is for general public reading I would suggest that Ga is not helpful, but one of the other two conventions should be adopted throughout. GSAckerman (talk) 10:41, 26 September 2014 (UTC)

Supercontinental climate

Continental climates are characterized by extremes of hot and cold - would these extremes be increased within a supercontinent? Pendragon39 07:17, 20 September 2007 (UTC)

"Relation to evolution" section

This section is more than a tad unencyclopedic, not least because of its grammatically improper title... What may be sound paleobiology by some people's judgment, reads like unrepentant Darwinian pontification. If this theory is so sound, its merit could be better evidenced by citation of reliable sources. As it stands, the entire section appears to be of equal merit with speechificatory knowitallism. Tomer^talk 09:00, 18 June 2008 (UTC)

Three stages

I seem to recall reading somewhere that the earth has passed through 3 stages. in the first stage all the continental and oceanic plates floated on an ocean of lava. in the second stage the deepest roots of the continents became grounded. we are living in the third stage where the earth is entirely solid down to the iron core. As I recall, this was presented as being important to understanding the continental cycles. just-emery (talk) 06:43, 2 July 2009 (UTC)

Graph contradicts article wrt age of Rodinia

The text of the article states: “The previous supercontinent, Pannotia, formed about 600 million years ago, […] the supercontinent before Pannotia, Rodinia, existed ~1.1 billion to ~750 million years ago.” But this contradicts the illustration, which places Rodinia as the immediate predecessor of Pangea. --Gro-Tsen (talk) 13:55, 16 February 2010 (UTC)

Seems that image ignores Pannotia, maybe remove the image? due to conflict with text. Vsmith (talk) 14:20, 16 February 2010 (UTC)

Moved Note

I have copy and pasted these three article into my user page: "Supercontinent (section)", "List of supercontinents" and "Supercontinent cycle". The new-and-improved lol article will be name "Supercontinent". When I am finished, I will move the new "Supercontinent" article to Wikipedia. This process takes me a month or two. Bettymnz4 (talk) 22:35, 5 April 2010 (UTC)

I edited the article on supercontinents a little bit, but don't worry we'll see when you are ready. Jpvandijk (talk)

Genetic Drift

According to Genetic drift, which I checked when this section conflicted with my vague recollection of Origin, and appears to be a fairly clear and well-sourced explanation, genetic drift *decreases* diversity, not increases it. (Darwin predates genetic drift as a concept, but he did sort of attack this from the opposite direction: larger populations support greater diversity due to an increase in opportunity and competition, and therefore selection, effects.)

There is a more subtle point here: when a small sub-population is isolated from its parent population, genetic drift effects become more important causing diversity *within* that sub-population to decrease, that is individuals become more similar to each other over time than is the case for the larger parent population. They will also tend, as a whole, to diverge faster from the average of their parent population. So multiple small isolated populations as a result of continental rifting will end up at different points - which one might call "diversity" - but the term typically applies to variation within a population, not between populations. 86.26.14.250 (talk) 01:32, 25 April 2012 (UTC)

"Simplified sketch of the western part of Pangaea"

This sketch seems to be just a little bit _too_ simplified, being just a collage of modern shorelines of both Americas, Africa, Greenland and Europe positioned to (very roughly) resemble the shoreline of Western Pangaea. The use of modern European shoreline is especially dubious because it has formed relatively recently (no more than 50 MYA, and the modern-looking shoreline formed no more than 20 MYA, roughly the time of the collision with Indian plate) - before that Europe had used to be an archipelago of islands in the Tethys ocean. This image is not informative at all (more like confusing) and I suggest it being removed from the article. There are better depiction of Pangaea on the WikiCommons, too (e.g.). 85.140.2.15 (talk) 23:20, 18 March 2016 (UTC)

I agree, not great. I think the lead image at Pangaea is better. Maybe just use that one? Isambard Kingdom (talk) 23:27, 18 March 2016 (UTC)

I changed the image. See what you think. Isambard Kingdom (talk) 23:39, 18 March 2016 (UTC)

Space impact & tidal locking

Has the breakup of a supercontinent ever been tied to an asteroid or other Space impact? SharkD  Talk  10:43, 13 November 2016 (UTC)

Also, what about tidal locking with the Sun or Moon? SharkD  Talk  05:02, 15 November 2016 (UTC)

Ur and Vaalbara: Incompatible reconstructions?

This page gives the impression that vaalbara is a predecessor to ur and that both are compatible, but the page on ur claims that only one of them could have existed in the proposed manner. Could someone fix this discrepancy? — Preceding unsigned comment added by 2601:247:C780:2630:78C8:6588:39E6:CD9B (talk) 04:31, 23 March 2019 (UTC)