The statement implies that by "Earth's center" the authors mean the center of mass, that being the point about which the body as a whole rotates. The oceans ho

The statement implies that by "Earth's center" the authors mean the center of mass, that being the point about which the body as a whole rotates. The oceans however are part of Earth's mass, and kept in motion relative to the crust by tidal forces from the moon. This too, the piece neglects. Calculation of the magnitude of tidal effect might be a fun exercise for someone whose calculus skills are less atrophied than my own ...