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I want to use Earth for my setting, but also want to alter its continents and tectonic plates to look more fantastical than before. If an ancient alien terraforming fleet arrived and was able to affect one or more significant variable to planet Earth (gravity, time, etc.) temporarily, what would best enable the altering and reshaping of Earth's tectonics and continents within a mega-year (1 million years)?

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  • $\begingroup$ "affect one or more significant variable to planet Earth (gravity, time, etc.) temporarily" - would it be like in 1 million years 100 million years of geological history has passed? $\endgroup$
    – Alexander
    Sep 18, 2020 at 16:23
  • $\begingroup$ @Alexander Yes. $\endgroup$ Sep 18, 2020 at 16:27

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Heat up the Mantle

Specifically, heat up the mantle as unevenly as possible.

The exact mechanics behind plate tectonics is still being studied, but a prevailing theory is that it has to do with convection currents in the mantle. If the alien's goal is just to speed up plate tectonics they might want to just heat up the core of the earth. This will cause the mantle to heat up faster and cause convection currents to move faster. The mantle will then push around tectonic plates faster, accelerating normal tectonic motion. Cooling down the crust could also help to prevent the mantle from reaching a new (higher) stable temperature.

What if this isn't enough for the aliens? Then they might want to start heating (and cooling) the mantle directly. Heating a certain area deep below where they want to break a tectonic plate will cause a large upwelling of magma. Once the magma gets to the surface volcanoes will form, and with any luck, the tectonic plate will crack apart. At this point the aliens may want to cool the heated magma back down and heat the magma that sank to the bottom of the mantle, essentially accelerating the usual convection process.

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  • $\begingroup$ How hot, necessarily? Could it be done by detonating several high-yield nuclear explosives in the core, for example, or by harnessing the power of the Sun and inserting said power into the core? $\endgroup$ Sep 18, 2020 at 15:14
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    $\begingroup$ I'm not an expert on this but here are my estimations: According to Wikipedia the earth's internal heat flow is about 47 TW, and the energy in an atomic bomb is about 80 TJ. That means to double the heat of the core you'd have to detonate an atomic bomb every two seconds. The sun on the other hand, produces about 380 YW, which is more than enough energy to significantly increase the heat of the core. The tricky part would be getting the heat to the core without heating up the crust, though your aliens might actually want to do that. $\endgroup$ Sep 18, 2020 at 15:22
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Your aliens could possibly make this work by increasing the acidity/salinity of ocean water to increase erosion on the continents. This would cause the total landmass to shift, over time, into the sea. Once there would be enough soil deposits from the erosion, new continents would be formed by the buildup of said deposits.

To make this even more drastic, your terraformers could increase or decrease the solvency of the ocean water, depending on whether they want a wetter or drier land. Increasing the solvency would cause the water to absorb more quickly into the soil, perhaps causing plants to grow more and an overall wetter climate. Decreasing the solvency would cause the soil to not absorb the water, causing more lakes to appear but drier soil. This water could be distributed by means of hurricanes or could be deposited directly into rainfall.

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  • $\begingroup$ That's not how new continents are formed. $\endgroup$ Sep 18, 2020 at 21:45
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Since you're not worried about life, and they can manipulate time (as mentioned above), that's all you need to do. Simply accelerate or decelerate the relative passage of time on Earth.

If they arrived, say, 200 million years ago and slowed down Earth's relative time so that, basically, Earth "now" would look like it did, say 100 million years ago, it would look like this:

enter image description here

If they, on the other hand, sped up relative time so that Earth "now" would look like with an extra 150 million years under the belt, it would look like this:

enter image description here

The actual layout would be a bit different because these reconstructions show overall layout, and thus keep things somewhat familiar.

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  • $\begingroup$ Note this is only one projection there are quite a few. There is a big question about what will happen to the pacific plate, it is possible that without a spreading center it may end up closing very quickly. there is also the possibility of a north American rift valley forming. $\endgroup$
    – John
    Sep 19, 2020 at 13:49

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