Under the oceans, often in their centers, are ridges -- called mid-oceanic ridges.
Graphic of worlds oceans depicting mid-oceanic ridges
These ridges are typically tectonically active. They can have flowing lava, earthquakes, venting of steam and other phenomenon. Studies of mid-oceanic ridges seem to indicate that the rate of activity varies in a cyclic fashion.
For example, it is known that the earth's magnetic orientation flip-flops in a cyclic fashion. What is now the north pole -- magnetically north -- becomes magnetically south. The south pole's magnetic field becomes magnetically north.
Graphic of earth North pole and south pole normal and flip flopped.
As the earth's magnetic polarity reverses, this recorded in the solidifying rock coming out of the mid-oceanic ridges.
Graphic profile of ridge with arrows pointing down the slopes and arrows indicating zones of flip flopping magnetic polarity.
If this occurred in a perfectly cyclic fashion, then the flip flops would be aligned like this,
Graphic of perfect periodicity in the changes.
However, apparently there are indications that the flip flops occur in cyclic fashion that speeds up and slows down and that may be gradually diminishing. Graphically, it might look like this,
Graphic of changing periodicity with sine wave and dampening characteristics.
This would correspond to a sine wave that is dampening,
Graphic of sine wave that is dampening.
By taking core samples from the rock flowing away from the mid-oceanic ridges and dating them, it is possible to estimate the number of years it takes for changes such as this to occur.
In analyzing the rock flowing away from the mid-oceanic ridges it is tempting for simplicity sake to assume that the rate of flow has always remained the same. Unfortunately, this assumption is not logical and greatly complicates the analysis of the ridges.
If the earth goes through cycles of increasing and decreasing gravitational force, then this variation of squeezing the earth with greater and lesser force could cause them to flow at greater and lesser rates.
Graphic compressing and decompressing earth zoomed ridge
An increase in gravity would compress the earth's crust, pushing up the ridges, possibly making them more active and having a greater flow rate. A decrease in gravity would decompress the ridges and reduce their activity.
Graphic of compressed ridge with faster flow
Graphic of decompressed ridge with slower flow