The insertion of an extra second in our lives has caused a lot of hilarity on the internet. The days are getting longer and the Time Lords have sneaked in an extra second to keep up the pretence that there are 3600 seconds in an hour and 24 hours in a day.
The main culprit is the moon. It causes tides and a lot of energy is lost as tidal waters slosh around. The loss of energy causes the earth to spin more slowly and the days get longer.
Clever people have done sums and come to the conclusion that the days are shortening by about 20 seconds every million years. That amounts to just a few seconds over the short time that our species (Homo sapiens) has been around. but think of the corals … they date back to 500 million years ago.
If the clever people got it right the days would have been a couple of hours shorter then. So where’s the evidence? Where’s the smoking gun that will tell us what was really going on?
If this was a police matter the forensic experts would be sent in. They would dig around for clues. Some sort of clock is needed and, by good luck, corals have one.
Like other living creatures, they have biological clocks and their ticking is recorded in the fossil record. Cross-sections of fossilized coral show growth rings. Put them under a microscope and you will see a yearly pattern, as in trees.
Now, increase the magnification and a daily pattern comes into view. By counting the number of day-rings to every year-ring, the number of days in a year can be found. It checks out. The days were a couple of hours shorter when the first corals appeared on Earth.