Clocks tell us that a day on Earth lasts for 24 hours, or 86,400 seconds. But that number is not precise and unchanging.
The exact length of a day on Earth depends on how long our planet takes to complete one rotation, and that often changes ever so slightly, thanks to dramatic events like earthquakes and volcanic eruptions, as well as more subtle shifts caused by the liquid metal in Earth's outer core sloshing around its solid inner core.
