Recently I downloaded the newest version of Google Earth. By default it was in 3D because my video card supported it. I didn't want it that way and I wanted it turned off. Here is how I did it.
You are looking for an option called Stereoscopic 3D. It is in the Nvidia Control Panel. If this is enabled, uncheck it and save it. Now close and reopen Google Earth. It should now be fixed.
I also had a bigger issue. If you can't find the Stereoscopic 3D option, here is how to enable it.
Stereoscopic 3D Missing in Nvidia Control Panel
OS: Windows 8.1
Video Card: Nvidia Quadro NVS 295