It has long been known (I was introduced to the idea in the 70's) - that the Earth's rotation is slowing slowly. Growth in corals for example is laid down when symbiotic algae are getting light during the day, on top of which you get other patterns imposed by water depth (phases of the moon); seasons and the year.
Cool to see geological time getting some news

Récupérer autant de précision, juste grâce à une palourde, c'est pas mal du tout.