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Could Mars' ancient tectonic activity have ceased due to its oceans having been composed of sulphuric acid, which warmed up and evaporated due to the Theia event as ice chunks landed on its surface? Strongly conductive liquid sulphuric acid on early Mars' surface could have been responsible for generating its core spin causing tectonic action which then all died off as a result of its oceans evaporating and thus removing the conductivity responsible for the core spin, whereas Earth's oceans didn't evaporate (because they are water) so can phase to ice ages to prevent overheating.

Why else would Mars have evidence of ancient alternately polarised extrusion from now ceased tectonic activity?

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    $\begingroup$ It doesn't sound very likely to me $\endgroup$
    – Slarty
    Mar 13 at 15:20
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    $\begingroup$ The hypothesized Theia impact resulted in a cloud of vaporized and molten rock, not flying chunks of ice, and the early solar system was regularly bombarded with ice in the form of comets. And of course the impact heating would dwarf anything from mixing of sulfuric acid and water. Apart from that, why would you expect ancient Mars to form sulfuric acid oceans in the first place? How would a conductive ocean generate core spin? How would core spin result in tectonic action? Where would that sulfuric acid have gone? This is just a long string of unconnected ideas and unsupported assumptions. $\endgroup$ Mar 13 at 15:39
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    $\begingroup$ @puffin there is also earth science that has the geophysics tag earthscience.stackexchange.com/questions/tagged/geophysics. Would suspect to be suitable there it would need a fair bit more detail on the proposed mechanisms collecting the sulpher, generating core spin and then evaporating. $\endgroup$
    – GremlinWranger
    Mar 13 at 23:19
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    $\begingroup$ The problems with the basic assumptions remain: the proposed explanation is a chain of non sequiturs. Apart from the implausibility of such sulfuric acid oceans or the problems with the ice idea, conductivity of oceans is unrelated to core spin and core spin is unrelated to plate tectonics. It seems they really are trying to ask why plate tectonics on Mars stopped and/or its magnetic field faded, and I suggest focusing on that. The answer almost certainly does not involve sulfuric acid oceans or Theia impact ice bombs. $\endgroup$ Mar 15 at 1:00
  • $\begingroup$ See Wikipedia. Surely it's worth comparing. Plate tectonics don't just happen; otherwise they'd be happening on lots of planets. There has to be a mechanism behind them. $\endgroup$ Mar 18 at 19:10
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First, tectonic activity have not ceased on Mars, although the planet is in a "stagnant lid" stage, which represents the last stage before a body becomes tectonically dead. See the answer to Is there convection in Mars' mantle?

Second, tectonic activity is caused by internal heat. As a planet gradually loses its internal heat, tectonic activity slows down, until it eventually stops. There is no need for more convoluted explanations.

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