All of them from the Indo-European root dyau which explains the similarity with Latin dies though the word is known to come from the Germanic branch.As of October 17, 2015 This makes the SI-based day last exactly 794 243 384 928 000 of those periods.
(See tidal acceleration for details.) The length of a day circa 620 million years ago has been estimated from rhythmites (alternating layers in sandstone) as having been about 21.9 hours.
The length of day for the Earth before the moon was created is still unknown.
Several definitions of this universal human concept are used according to context, need and convenience.
In 1960, the second was redefined in terms of the orbital motion of the Earth, and was designated the SI base unit of time.
In recent decades the average length of a solar day on Earth has been about 86 400.002 seconds (24.000 000 6 hours) and there are about 365.242 2 solar days in one mean tropical year.