20 things you didn't know about time

Interesting:

7 -- One second used to be defined as 1/86,400 the length of a day. However, Earth’s rotation isn’t perfectly reliable. Tidal friction from the sun and moon slows our planet and increases the length of a day by 3 milli­seconds per century.

8 -- This means that in the time of the dinosaurs, the day was just 23 hours long.