Talk:Supercontinent cycle
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[edit] 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)
[edit] 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)
[edit] 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)
