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Locedamius t1_jba821m wrote

How the continents look like is mostly determined by what is going on underneath the surface. Earth looks the way it does because of plate tectonics. We have several major continents with major landforms clearly linked to tectonic plates like mid-ocean ridges or mountain ranges often existing in one long line along plate boundaries. Other planets do not have plate tectonics. The topography on Mars or Venus was built primarily by shield volcanoes and erosion. I do not know why Earth has plate tectonics while Mars and Venus don't and I don't think anyone knows. It could be that the impact that created the Moon had an effect. It could be that tidal heating from the Moon's gravity helped (especially early on when the Moon was much closer). It could be that other factors were much more important and the Moon has barely any impact.

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Regarding your fictional world, how exactly did that cataclysm happen?

There are theories that Venus underwent a global resurfacing event some 300-500 million years ago, which covered the entire surface in lava and essentially erased the previous topography. Since then, Venus' surface was mostly shaped by volcanoes and wind erosion forming more or less randomly distributed highlands, which would be continents if Venus had water. If that sounds fitting for your world, you can look up Venus' topography for inspiration.

Mars has an interesting topography with the southern hemisphere being several kilometers higher than the northern hemisphere. With enough water, that would mean one supercontinent covering half the planet and one big ocean covering the other half. Why it looks that way is still an open question afaik, I have seen a theory that a big impact may have caused it. Anyway, if your god grabbed the material for the new moon exclusively from one side of the planet (quite likely, I assume the whole population that angered him lived on that Pangea-like continent), that side could become the new mega-ocean. In that case, the land and ocean in your world may have simply switched places and without plate tectonics or other major resurfacing events, they will mostly stay where they are.

If you want your world to have plate tectonics, you could look at models of Earth in the past and future to get an idea of which landforms are possible and how they could have developed over time.

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Aubin_kun OP t1_jbacodz wrote

Yeah I thought of this mega-ocean in the middle of everything. I just thought that this new moon could impact geography because of its presence.

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Locedamius t1_jbai7i6 wrote

It certainly has an impact on geography on a smaller scale if it is big enough. A moon the size of Mars would create huge tides that would impact the shores all over the planet. Large mudflats that stretch for many kilometers, connect islands to the mainland for a few hours twice per day while flooded during high tides could be very common features on your planet. Coastal cities would have to deal with tides several meters high and build accordingly etc. Of course, the smaller the moon and the further away from the planet it is, the less it impacts your planet.

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KnoWanUKnow2 t1_jbawirm wrote

Assuming that the planet is bigger than the moon, then the planet would have a much larger impact on the moon than the moon would have on the planet.

Look at the moons of Jupiter and Saturn. They are squeezed and compressed by the planet's gravity, which causes volcanism. Io is the extreme example, as it is closest to Jupiter. But Ganymede has a liquid ocean under it's ice largely because the gravity of the nearby planet is squeezing it and the friction is warming up the interior.

Also tidal locking is a thing. That's good for your story. A moon that is tidally locked to it's planet (like ours is) will always face the planet. From our perspective the moon doesn't rotate, it's always showing us the same face. That's why the moon has a dark side. Not because it's literally dark, but because before we invented spacecraft no one had ever seen it, it was unknown.

So your theoretical moon would have the city always facing the planet, to remind the planet's inhabitants of what happened (although it would likely be much to far away to make out the city). It could also be a sulphurous volcanic wasteland, much like the surface of Io due to tidal effects.

As for the moon's effect on the planet, that depends on the size of the moon and how close it is to the planet. Too close and too large and tidal effect will break the moon apart. You seem to have settled on a small, close moon which likely would have very little effect on the larger planet. As an example the 2 small moons of Mars have almost no effect on the planet at all.

Our moon causes ocean tides on Earth. It may also have an effect on plate tectonics, not so much with moving them, but may be at least part of what's keeping them apart and not allowing them to bind together (The jury is still out on that one, the oceans being subducted and releasing water seems to play a much larger role). On the other hand, the Earth caused the moon to become tidally locked and also causes a regular pattern of moonquakes.

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austinmiles t1_jbdapl4 wrote

There are also moons that have such a strong reaction to their planet that they have geological activity. Enceladus and Europa both have liquid oceans because of the heat generated by tidal flexing.

If your moon was large enough it could cause enough upheaval that over a long period of time it could change the landscape either through much more active tectonics or from things like volcanos which could look very different.

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Josephdirte t1_jbad0eb wrote

It's been a long while since I studied this stuff, but I believe the heat generated through the natural decay of uranium, with the insulation of earth's rocks, causes differential heating to the interior of the earth, creating convection cycles within the mantle. This drives plate tectonics

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Locedamius t1_jbafrmh wrote

Kinda true (slab-pull also has an effect but it sort of needs plate tectonics to already exist to drive plate tectonics) but that's happening in all planets, so what is special about Earth that it developed plate tectonics while Venus or Mars didn't?

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toastar-phone t1_jbby0mf wrote

I don't think I've read anything on it but in theory it doesn't seem out of place to imagine there are tidal effects of the moon on the mantle which could cause 2nd order effects on plate movement.

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xenona22 t1_jbcvngp wrote

Hold up a sec because Europa is contorted by the gravity of Jupiter and causes it to shoot giant plumes of water into space

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