Aha! Now we're getting somewhere! When the particles started clumping together why did some form round planets and stars but some a flat earth?
It is likely that in the past, Dark Energy was a much more rigid flux, and so the Earth formed as layer upon layer of molten rock was compacted onto itself with nowhere to go due to the inertia of the rock in front of it. It would have accelerated at a phenomenal rate during this early formation; perhaps millions of metres per second per second. As the rigid Dark Energy struck the flat underside of this large cooling disk, a large region in front of it, extending for millions of kilometres, was shielded from the Dark Energy, allowing for spherical bodies to form, most of which plummeted straight into the surface of the Earth. As the initial rigidity of Dark Energy subsided for reasons not fully understood, the acceleration of the Earth slowed and the region that was shielded from Dark Energy began to shrink, until finally the heavens as we know them today were struck by the force of Dark Energy and caused to remain where they were.
Dark Energy is still becoming less rigid and less powerful, so in a few billion years we will likely be accelerating much more slowly, and more of the upper atmoplane will have stopped being shielded from Dark Energy and will escape into space, causing much lower air pressure at the surface. The oceans will eventually evaporate due to low pressure, creating an uncontrollable greenhouse effect and the Earth will overheat before Dark Energy spills over the ice wall and acceleration stops altogether, at which point the Earth will be left to slowly cool and eventually collapse into a sphere.