Enlarge (credit: Roman Studio) Because most things about Earth change so slowly, it's difficult to imagine them being any different in the past. But Earth's rotation has been slowing due to tidal interactions with the Moon, meaning that days were considerably shorter in the past. It's easy to think that a 22-hour day wouldn't be all that different, but that turns out not to be entirely true. For example, some modeling has indicated that certain day lengths will be in resonance with other effects caused by the planet's rotation, which can potentially offset the drag caused by the tides.