The sequence you are referring to ("the earth splitting into two planets"), is actually a huge asteroid hitting earth, because the whole sequence is reversed.Lucy is going further back in time, observing how the earth was formed, and before that, how the galaxies were scattered across the universe and ultimately culminating (backwards) to the origin of the universe, the Big Bang, the explosion of a singularity or single point which contained all the energy in the universe (not sure about the physics here). She performed all of this with 99% of her brain's power. Once she reaches the big bang the screen shows 100%.
Then, the shot goes back to the room Lucy was in with the scientists, but her physical body disappears right before Jang fires his weapon. Then Jang gets shot, and the "moving computer" (Lucy?) produces a pen drive with a space-like (starry) texture, which I think represents all the knowledge Lucy gathered in that sequence, and which she made available to mankind.
Finally, Del Rio asks the scientists: "Where is she", and Lucy displays the answer on the man's own cell phone:"I am everywhere", which indicates she became an omnipotent, god-like being.
I believe, based on this last scene, that the director's opinion is that no human will ever reach 100% usage of his/her brain, because that would mean becoming a god. Is god a being that can use the full potential of their intellect? Interesting ending for this movie.