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RLarsen
2007-Apr-08, 01:13 AM
I've been catching up on old podcasts and just finished the episode on the origins of the moon. A remark was made, that the Big Impactor put Earth on re-set. Could this re-set have also been the cause of the plate tectonics on Earth? It seems to me that such an impact could well have fractured up the crust, sort of like the shell of an egg cracking when thrown.

(I understand from other sources, that it is thought that Mercury also suffered a big impactor, giving rise to the Caloris Basin and the "Weird Terrain" at its antipode. Here though, the whole crust was blown off, hence no tectonics.)

alex.blakes
2008-Aug-02, 12:43 AM
I've been catching up on old podcasts and just finished the episode on the origins of the moon. A remark was made, that the Big Impactor put Earth on re-set. Could this re-set have also been the cause of the plate tectonics on Earth? It seems to me that such an impact could well have fractured up the crust, sort of like the shell of an egg cracking when thrown.

(I understand from other sources, that it is thought that Mercury also suffered a big impactor, giving rise to the Caloris Basin and the "Weird Terrain" at its antipode. Here though, the whole crust was blown off, hence no tectonics.)

Well, it seems to me a good idea, but then again there's a pretty big flaw. This big impactor would either have skimmed one side of earth or have had a direct impact, but in either case would have no doubt have shattered the crust at and around the place of impact, but have left the crust on the other side of the earth more intact. If indeed this was the cause of plate tectonics, then it seems logical that one side of the earth would be littered with very small plates. As it is techtonic plates of different shapes and sizes are evenly distributed across the earth.

On the other hand there are a couple of reasons why i would suspect that plate tectonics started in a different way. What seems most likely to me is that the earth's molten core was a direct cause of plate tectonics. Because the earth's mantle is molten there are convection currents in the mantle, where hot magma rises near to the earth's crust, and when the magma cools it sinks back down to the core. This is a continuous cycle. This movement of the magma generates friction against the crust, and causes plates to move. I suspect that if the earth crust was intact, the friction from the moving magma would actually cause tears in the crust, eventually breaking it up into all the plates we now know today. Having said all that, it's suspected that this big impact gave the earth it's moulten core in the first place... so indirectly the impact may have caused plate tectonics