Sinking mantle

Some years back Stripe recommended the video series by Calvary Chapel on earthquakes. 2 sermons about an hour each in 6 or 7 parts. Part 2 is more interesting. Kevin Lea defends Walt Brown's Hydroplate Theory.

The theory as it applies to the Flood is that the earth had significant water below the crust which was released through the crust along the midatlantic ridge (and around the earth) causing flooding and a contra-spherical depression which became the pacific basin. Importantly the model specifies that the continents moved over the mantle due to gravity until they struck opposition which led to upfaulting (mountains) and downfaulting (trenches). The model does not claim that some plates are subducting over or under other plates, though these regions represent real faults. Thus the Hydroplate Theory is distinct from Baumgardner's Catastrophic Plate Tectonic Model.

The relationship to earthquakes is the theory's claim that the inside of the earth consisted of a solid mantle but no core prior to the flood. As a result of stresses within the mantle, rock melts then rises or sinks depending on the surrounding pressure and resultant density. Lower pressure shallow mantle expands and decreases density when it melts therefore rises; high pressure deep mantle shrinks and increases density when it melts therefore sinks. The depth at which mantle changes from expanding to shrinking is called the transition zone. These changes in density and volume mean that other mantle surrounding it moves and the transmitted movement is felt as an earthquake. Rising melted mantle also surfaces in volcanic eruptions.

There is more detail than this; I have not read Brown's book, this is what I gleaned from the video.

Of interest is that because mantle melts and shrinks at certain depths, it must sink and cannot rise. So it will form a core. A liquid core with (the relatively) lower pressures and resolidifying to form a solid core with higher pressures. This results in an inner solid core and outer liquid core which can only grow as mantle continues to melt, shrink, and then sink to the core. Because it has shrunk (increased density) the volume of the earth must decrease. This seems to be the case concerning the mantle regardless of whether the hydroplate model is correct: every time mantle rock melts below the transition zone it sinks to the core never to rise again.

On hearing this my first thought was if the volume of the earth shrinks then its spin will increase (assuming no change in mass) due to conservation of angular momentum. The speaker subsequently discussed this same issue.

If there were significant changes at the time of the Flood this could alter the measured duration of the year and month. More on this to come.