staionary air next to the surface. On a flying surface this is just
a few millimeters thick.

Even the boundary layer on an a/c isn't completely motionless. That's
only true very near the surface. The boundary layer ends when the
speed of the flow is 99% of the freestream velocity.

The boundary layer on an a/c thickens the further it goes; the wind on
the planet Earth flows for hundreds of miles, not just a few feet.
Seems like the difference between the Earth's boundary layer and that
of an a/c is a matter of degree, rather than kind. But I'm only
guessing. ;-)