Dear Andrew.Nowicki.00:

wrote in message
oups.com...
The Earth's crust is made of two layers called sima
and sial. Sima is the lower and denser layer. It is
made mostly of basalt. Sima is 5 to 10 km thick and
covers the entire surface of the Earth. Sial is 20-70
km thick and covers only 30% of the Earth's surface;
this is the elevated part of the Earth's surface called
continents. The remaining 70% of the Earth's surface
is covered with oceans. Sial is sometimes called
granitic layer of the crust, because it is made mostly
of granite, which is made mostly of silica
(SiO2 content = 72%).
....
It is very difficult to imagine any geological or
astronomical event that could selectively scoop up
sial from 70% of the Earth's surface.

I can imagine such a thing. Impact Earth "off-center" with a
massive object of composition similar to what we have now. The
differential rotation imparted to the combined object starts a
wave, that ends up being a single lobe. The lobe is elevated
above the "nominal" surface of the Earth, which will selectively
"sort" lighter materials from denser materials. As the lighter
materials are collected in the lobe, the amplitude gets higher,
until it ultimately it pinches off. The Moon is born.

David A. Smith