Gonnerman must have a very narrow knowledge of earth science
There are rocks discovered in Western Australia that have been dated between 3.8 and 4.5 billion years old.
That has to be bloody close to the formation of this planet
So what is Gonnerson's waffle all about?
It is clear that all materials on the planet have not been recycled otherwise these specimens found in Western Australia would not exist
Therefor Gonnerson's discovery that not all material has been recycled isn't telling us anything we didn't already know. Unless Gonnerson is going to tell us that this particular area in Western Australia is unique in the whole planet being the only piece of the planet that at some time has not been recycled
I suspect that at some time in the future other similarly ancient rocks will be found in other parts of the planet
With respect to the mantle it's convection currents move exceedingly slowly and whatever melting occurs would only melt the portion in actual contact with the magma. That would leave most of the mantle unmelted and it would be reasonable to expect that as this process continued that further parts of the mantle would be melted as they having been exposed by an earlier contact with magma would also be melted.
What Gunnerson needs to do is to calculate how long it is likely to take for all parts of the mantle to have at some time had sufficient contact with magma to have been melted.
It may transpire that this will never happen because the currents may operate in such a fashion that some parts of the mantle will never be exposed to magma