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The movement of the tectonic plates in the Earth's crust is quite a small amount, at only a few centimetres a year. How fast could the movements of a tectonic plate get up to if an earth-like planet:

  • Had an inner core made of a substance that emitted more heat (about twice the amount of Earth?)

  • Had a mantle considerably thinner, allowing magma to move faster along the convection currents

  • Had a smaller distance between the core and the crust

Please note that these are all criteria for the same planet, but feel free to explain if they cannot fit together to create a feasible one.

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    $\begingroup$ Ummm, if you hold on for a few months, I will have finished the book that covers all of your questions. $\endgroup$
    – Justin Thyme the Second
    Feb 3, 2021 at 19:18
  • $\begingroup$ Welcome to worldbuilding. Please consider narrowing down your post to a single question instead of the 7 I count now. And make sure that you comply with the criteria listed in our help center. $\endgroup$
    – L.Dutch ♦
    Feb 3, 2021 at 19:26
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    $\begingroup$ Are these points meant to be considered separately or as a list of criteria? "Smaller distance between core and crust" and "smaller than Earth" are redundant, as are "thinner mantle" and "lighter tectonic plates". But you've also got some inherent conflicts: "smaller than earth" and "emit more heat" are tricky to fit together and imply a shorter geological lifespan (smaller things cool more quickly) and a younger planet, which is less likely to harbor life $\endgroup$
    – Punintended
    Feb 3, 2021 at 19:37
  • $\begingroup$ Thanks for the feedback on my question. First, yes, they are all criteria for the planet (the same planet, not just different scenarios) but I can see how it can be interpreted as many questions. I guess that "smaller distance between core and crust" and "smaller than Earth" are basically the same - I will amend that - and, yes, I am willing to accept that the planet may not be able to sustain life with a shorter lifespan. $\endgroup$
    – P C I A
    Feb 3, 2021 at 21:04
  • $\begingroup$ Actually, I take it back - there could theoretically be a proportionally larger core and smaller mantle. And though I phrased it poorly above, the shorter geological lifespan / younger planet aren't as conducive to sustaining new life. Those aren't necessarily issues for humans trying to colonize it $\endgroup$
    – Punintended
    Feb 3, 2021 at 21:57

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Geologist here!

The internal heat of Earth's mantle and core comes from the radioactive decay of various elements. To give an Earth-like planet a hotter mantle, you'd need to have more of those elements present when the local solar system formed.

A less viscous mantle would mean that the process of convection moved faster, and it would also likely make volcanic eruptions more common and more dangerous. In real life, lava doesn't normally move too fast- you can outrun it on foot. The real danger is pyroclastic flows and toxic gases.

To have a smaller distance between the core and the crust, you'd need to have either a larger core or a smaller planet. Most of the Earth's volume is the mantle, so making it thinner would require some major changes. A larger core would make gravity much stronger, since it's the densest part of the planet, being an iron/nickel alloy. This would also speed up convection, since the "hotter magma rising/cooler magma sinking" cycle wouldn't take as long.

The changes you proposed would lead to tectonic movement being faster, but they might also lead to your hypothetical planet being uninhabitable for humans.

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