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Actually we only gain 1.3 milliseconds every 96-100 years, not 1 second every 1.5 years! :) the shortest known Earth day was 6 hours and the longest is 24 hours & 2.5 milliseconds (today's current day), in 1820 the day was exactly 24 hours, but since it's been nearly 200 years we've gained 2.5 milliseconds to our day.
Let's suppose we have a spaceship with the exact speed of light. If a traveller takes this spaceship to go to proxima centauri (approximately 4 years light away from Earth) and come back, we (as observers on Earth) will see the ship coming back after approximately 8 years. But how much time would have passed for the traveller on the ship?
Moon orbits Earth in same direction as Earth spins as result we have tides. Tides are experience a drag, so as an outcome speed of earth is being reduces. To sustain angular momentum Moons gains energy and increases distance to Earth (at the beginning of Earth and Moon history day was 4 hours long and Moon was much closer).
For example, the average value of (0,0,0,4) is 1, not 2. Earth's orbit eccentricity is not 0, nor the Moon's one, so your distribution of day duration is probably slightly asymetric, hence the 4 seconds discrepancy. Sum all day duration of a year, divide by the number of days, you will get a better value.
$\begingroup$ Can you elaborate on how precession changes how long it takes the Earth to complete an orbit around the sun? I am having a hard time seeing how a wobbly axis could either change the length of a day or the speed at which the Earth orbits the sun - and 20+ minutes/year seems like a big difference. $\endgroup$ –
The Inverse Square Law dictates that if the Moon were half the distance from the Earth, its gravitational pull on our tides would be quadrupled. 1/3 the distance, 9 times the pull. Everything would drown twice a day. Approximately 1.2 billion years ago, the Moon would have been touching the Earth. Drowning would be the least of our concerns!
The dinosaurs would have flown off the earth. If the deceleration rate is inaccurate by 95% (assume it is slowing more slowly), then 250 million years ago, it would be spinning at 213,000 miles per hour. Also, given the fact that the moon is receding from the Earth, the effect the moon has on the Earth would have been greater in the past.
Mountains will disappear. Friction between the atmosphere and the Earth will be much reduced. The other factor, Earth tides, is also very small. That range of a 25.5 to 31.7 hour long day might grow a bit in the four billion years between the end of the oceans and the five billion year figure cited in the question, but not by much.
That the Earth has an equatorial bulge is a consequence of the second law of thermodynamics. The Earth's surface is an equipotential surface where potential energy is computed from the perspective an Earth-fixed frame (a frame rotating with the Earth). Anything but this would violate the principle of minimum energy.
The answer is given graphically by this figure, where you can see that the summer variations of the length of day are completely symetrical with respect to the winter variations. If you average the length of day over one year, whatever is the value of the latitude $\phi$, the mean length of day is exactly 12 hours. That is true everywhere on Earth.