Love the topic. Not my field, but a little research provides what I think are fairly clear explanations for the earth's lack of sphericity. The most general answer is that our planetary mass is unevenly distributed, creating areas (such as the Hudson's Bay) with proportionally different masses compared to other parts of the globe. In Hudson's Bay the lowered mass is probably caused by a combination of convection pulling the continental plates below the mantle, and by the Laurentide Ice Sheet, which was bigger than your momma's butt and squished the surrounding area down and to the side, redistributing the area's mass. Because, as you noted, gravity is proportional to mass, the gravity of the Bay area is 4% less than the average gravity of the planet. The greater influence is convection, and I don't think you need much more than that to explain the planet's lack of sphericity, although anything that changes the mass/gravity of a geographic area will have an effect - including meteor impacts, and if there was a Great Impact from which the moon was created you'd think it would have to be factored in...although I have yet to see that mentioned. The "normalization" you're talking about is called "true polar wander" - the planet's attempt to redistribute its mass along the equator. I'm imagining it as a centrifugal effect, but could be talking out of my ass.

I think that accounts for the small irregularities. But i don't think those factors alone can account for why there is far more landmass on one side than the other. And then there is the common understanding that this was at one point even more lopsided with Pangaea being on one side with nearly the rest of the globe being ocean (as i understand it) 

I certainly need to research the topic more myself. I know i'm not the first to propose the moon as a product of an impacted earth. But i have not seen any suggestion that the effects of the impact could also be the cause of the planets current shape. 

Plate tectonics is the single most powerful force in nature. A lot of people don't know that but its a facf! That is a fine observation!

Yes, I'd love to see an expert calculate how many irregularities tectonics/volcanic activity can account for. 

That's just mass above the surface of the water though, plus the earth isnt spherical its more pear shaped or egg shaped with the moons gravity taken into it. Also, the above sea level land is literally nothing compared to the rest of the earth as a whole

the moon moves around the planet. As far as i know there are no gravitational effects that give a permanently altered shape to the planet.

The earth is roughly round.... but the shape that it is, is secondary. What shape does it was to be. As far as i can tell, it should be trying to revert to an even sphere as best it can. A process that no doubt would take millenia...But one that should occur.

Two aspects i didn't account for. the magnetic field and its varying strnegth. The convection currents of magma. Both could have an impact on the planets shape. Though i still feel that neither could amount to the difference between the continents and the oceans.

My understanding of it is...

The structure of the planet is based upon density. The deepest point in the earth is commonly referred to as the Iron Core however it is not pure. Denser materials than iron (including gold) would make a core within a core. Above the core is a mass of molten rock being the next lightest. This is followed by the tectonic plates of the crust, the ocean and finally the atmosphere.

The forces acting on the planet and its polar nature are due to the movement of magma in an overall pattern that involves it sinking at the north pole and rising at the south pole. The pattern is like the copper coils on a magneto or motor. The movement of the magma over the iron core generates a magnetic field which gives us our north and south poles.

Tectonic plates are big solid pieces of the earths crust floating on this slow moving stream of molten rock. The plates act as insulators trapping the heat inside the earth. The continental plates are very good insulators because relative to oceanic plates they hold quite a bit of air. Having oceans above them any heat that does pass through the oceanic plates is quickly radiated into the ocean, then atmosphere then space. So the Magma beneath a continental plate is hotter.

The continental plates are also lighter (due to lower density) than the oceanic plates and so float higher and are more prone to be shifted by the current.

At the moment the flow of the magma is northwards and so all of the continental plates are slowly being dragged northward. Eventually the Northern super continent (Laurasia) will form centered on the north pole. When this occurs the greater amount of insulation covering the north pole will cause the heat at that point to increase relative to the now oceanic south pole. The northward flowing stream of magma will slow, stop and then reverse. The magma will now rise at the northpole flow south before sinking at the south pole and moving northwards at depth. A compass at this point would point to what is now the south pole. 

Or at least that's my understanding of it.

That all sounds accurate to my understanding.

My proposed ideas are the results of those factors over say 1-2 billion years. The cyclic nature of the convection currents in the molten parts, the movement of the tectonic plates and recycling/reforming of the crust..... should in theory (afaik) lead to even layers of even density.

We don't have even layers of even density, and i can't think of any aspects of the processes that would lead to it being uneven, except of course impacts... which obviously have occurred.

We can safely say that there have been very large impacts, but never any large enough to completely destroy the planet.. lol... Now... if my theory is right and the lopsided nature of the planet is due to a very large impact, I am quite sure it would have to have been larger and earlier than the one that took out the dinosaurs, If indeed that is how that happened. 

Propose we removed half of the planet, just clean cut and removed. The remaining half would be subject to half the forces previously present, but due to them being completely out of balance, the planet would very quickly attempt to get back to a spherical shape. The same can be said for removing a quarter, an eighth etc etc. The smaller the removed portion, the less uneven the remaining forces and the slower its 're-normalising' process would be.

What would that process look like say, 1 billion years after say 5% was removed. If it hadn't yet returned to an even sphere... you would have a slightly lopsided sphere, that is now far more even than it was immediately after the removal of the 5%.....

-----------------------

Side note.... A lopsided planet in the gravitational field of a larger body (the sun) would attempt to get into a tidal locked position, This would be due to the side of the planet with more mass having a greater pull than the side with less mass. The moon for example is tidal locked.

I believe this is the process that is slowing the rotation of the earth. What caused that rotation.... Impacts.... OR it is rotational speed left over from the planet forming. If you take the current decreasing speed of rotation... and assume it has been decreasing at the same rate since forming.... It would (i believe) be spinning WAY too fast back when it formed.... So we have to assume that the current spin (or at least the factors slowing it) occurred between formation and now.....

Blah blah blah.... I might be wrong, i often am.... But if i am not mistaken.... given enough time, we would end up being tidally locked with the moon and with the sun (not sure which first, moon is my guess)  For that to not happen, we would either need forces to go against the decreasing speed of our planetary spin. OR we would have to lose the lopsided shape :) 

All of those occurrences... i believe... have had plenty of time to take place since the planet solidified... leaving the only remaining thing.... A huge impact. One so large it made the planet misshaped, Gave us a lot of rotational speed.... and based on no calculations.... it would also likely be enough to dislodge more than 1% of the planets mass.... my guess would be 5%+ 

Where is the debris? 

The moon seems to be very similar in composition and is roughly 1.2% of the earths mass... we also have lots of meteors that have regular and predictable orbits that often come close. Of course... with an impact of that size, you'd also expect a lot of mass to achieve escape velocity and end up in orbit of the sun. Not sure if it would have the force required to eject stuff from the solar system entirely... my guess there is doubtful... lol....

Ok essay over now... :)