[Jan Martense]

I have a background in geology myself and I'm super glad you brought the subject up. So much that it prompted me to register an account.

My main argument is that the only theory that matches the criteria is plate tectonic theory. The theory that the Earth is made up of several segments, varying in oceanic and continental crust, that are all moving due to forces in the mantle at various directions and speed and are responsible for the formation and destruction of the crust. My issue is that plate tectonic theory can't work on a two-dimensional plane. With the known positions of plate boundaries and their movement speeds, the shape of the Earth would never be able to maintain a circular disc like structure. Instead it would constantly change shape, literal gaps would form in the crust based on the popular flat earth model, the Antarctic wall would be moving. If you believe in an edge, plates would be falling off it.

I am interested to hear what you believe is happening with the Earth's tectonics. What is causing all of the the observable phenomena listed above? Do you believe in plate tectonic theory? Or is there another theory that would allow for this to all occur on a flat plane.

Here's what I would say: firstly, I totally agree that the evidence for plate tectonics is overwhelming. As you mentioned, we can literally see the plates moving apart over the span of of few years in some places. The movement of hotspots is another compelling proof that laymen can easily understand. And structural geology offers visual evidence of the incredible forces which move and deform rock; forces which in some cases are so immense that they would require movements on the scale of a continent to create.

But that being said, I do NOT think the existence of plate tectonics necessarily disproves Flat Earth theory, at least not in the ways you mention. The "literal gaps" you claim would form are inconsistent with mainstream geology, where new crust which would "fill in" those gaps is formed constantly. Moreover, the fact that all plate movements can be accounted for on a round Earth suggests they could be accounted for in a disklike flat Earth as well. If we imagine the Antarctic wall and the plate underlying it as "stationary," then all faults bordering the Antarctic plate would either be transform, divergent, or convergent (obviously) and in no case would they "change shape"; the convergent plates would merely form a subduction zone and be forced under the more massive Antarctic plate. If said plate is truly disk-like, then it is not only possible, but necessary that it remain stationary relative to the smaller plates it encircles.

The force behind plate movements is not dependent on a round Earth either. They are caused by convection currents in the Earth's interior, which are themselves primarily created by radioactive decay.

So basic plate tectonics works equally well under both flat and round Earth theories, although there are certainly many details and mathematical models which would need to be adjusted.

[Iceman]

Agree the idea of plate tectonics working on a flat earth is not a problem in itself.

The issue(s) come up whe  you consider all the other factors around plate tectonics... if the earth has an edge(s), then where do the subducting oceanic plates along the Antarctic ice wall end up? What is the source of heat to melt significant thicknesses of rock in the mantle? How thick is the mantle/crust/earth's disk/puck/cylinder?

The wiki addresses some of the major geologic processes, but leaves a great deal out. It theorizes a subduction margin along the Antarctic continent/ice wall...but we actually know where that margin lies and how it interacts with other plates. The trans Antarctic mountains, fossil groupings, and bedrock stratigraphy in antarctica all combine to suggest that it hasn't always been a single plate, nor has it always been at the south pole. When it wasnt there, what was keeping the oceans up?

It's not that plate tectonics definitively couldnt work on a flat earth, it's that the accumulation of all the observations and our understanding of geologic processes all fit perfectly within a round earth.

I grant the common argument from flat earth proponents that the shape of celestial bodies doesnt bear any significance in discussing the shape of the earth. But if you ascribe to that belief, then there should be much greater weight on using our understanding of what happens here on earth to building our understanding.

There's my 2 cents...