When did plate tectonics start? http://en.wikipedia.org/wiki/Plate_tectonics
That's a bit of an open question; but it seems there are indications that it began very early; as much as 4 billion years ago. This is associated with new ideas about the "Hadean" (Hellish) era; it may not have been as diabolical as previously thought.
Here's an article from the NYT which discusses these ideas: A New Picture of the Early Earth. The relevant science article is
Hopkins, M. et. al. (2008) "Low heat flow inferred from >4 Gyr zircons suggests Hadean plate boundary interactions" in Nature 456, 493-496 (27 November 2008) doi:10.1038/nature07465
Cheers -- sylas
Perhaps a little at a time. Might south Pacific, with any example of colliding oceanic crust, with subducting, be suggestive? That is for 2 Archean brittle pieces colliding, with one somewhat cooler, and hence denser, might subduction occur? Might such localized process be occurring planet wide? Of course one could have ongoing mantle differentiating.
Is perhaps Mars an example wherein plate tectonics never started? Might any uniformity (i.e. no layering) to Vallis Marineris walls be consistent with no plate tectonics there? Is Mar's major volcano Olympus Mons consistent with no plate motion on Mars? Might uniqueness of 1 major volcano on Mars relate to uniqueness of Hawaiian plume? That is, might respective persistence suggest an ancient impact, and ongoing active deep conduit system? http://en.wikipedia.org/wiki/Mars
Actually, Mars likely did have plate tectonics when it was young with a significantly molten interior. However, since Mars is so much smaller than earth, it has cooled off and there is no longer the convection necessary to move the plates.
If one thinks of earth and Mars as heat engines, then the work they try to do is force x distance. In other words, resulting in plate motion. However the Mars heat engine (.3 earth mass) would not seem sufficient to result in plate motion. The very large size of Olympus Mons would seem consistent with no plate motion.
... it would need to be correct or.. no cigar.
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