Recently, it has come to light that the relative rotational speed of Earth's core seems to have a decades long cycle of leading and lagging the surface.
Internal dynamics are weeeeird.
Wonder if the moon affects this.
If both Mars and Venus have liquid cores and not much in the way of a magnetic field, it seems like there must be more to it, and it's likely to be one (or a combination) of factors that makes Earth unique in the solar system.