https://www.seeker.com/ice-age-clues-help-explain-mysterious... is one of many.

Note that if the day slows by 5.5 ms from 24 hours, then we need an average of more than one leap second per 6 months to keep up. Per https://en.wikipedia.org/wiki/Earth%27s_rotation the Earth's rotation changed by 1.7 ms in the last century, an average of 2.3 ms in last thousand, and it is being affected by a variety of causes right now.

Our moon is slowing down Earth's rotation by tidal friction (angular momentum is transferred from the Earth to the Moon). The effect is rather small with the period only slowing down by around 2ms per 100 years currently (depends on the configuration of the oceans and the orbit of the moon).

But internal changes in the Earth can also cause changes in the rotation period. For instance the 2011 Tohoku earthquake shortened the day by 1.8 us [1].

[1] https://www.earthobservatory.sg/blog/how-did-2011-tohoku-ear...