Q. Isn’t the suggestion of an ancient Earth spinning more rapidly a more plausible explanation for a reduction in gravity?
A. We can calculate the reduced gravity on the ancient Earth from the relative size of ancient life compared to present day life. These calculations indicate that gravity was about 0.3 the present gravity 300 million years ago, increasing to 0.5g during the dinosaurs’ time with gravity gradually increasing over time to its present day value.
The gravity reduction due to the Earth’s present rotation is only 0.003g. The Earth would have to spin very fast to reduce gravity to 0.5g. Evidence from Devonian corals indicates that there were 400 days per year about 388 million years ago which would speed up the Earth’s rotation so there were only 22 hours in a day if the Earth was in the same orbit around the Sun. If the Earth was spinning 1.1 times faster than now the force due to this faster rotation would still only be 0.004g - this is nowhere near enough to affect the scale of life.
On the other hand, on an Increasing Mass Expanding Earth the calculated gravity would be very similar to gravity predicted from ancient life. This is why I think the most probable cause for a Reduced Gravity Earth is an Increasing Mass Expanding Earth.