A big rock from space could split the crust, or at least punch a
hole in it. (And this has happened! And on several occasions.)
We've had some really, really big hits, including one that is
thought to have resulted in the capture and formation of the moon.
A hit that massive didn't simply split the crust, but nearly ripped
the earth apart. There is also the action of tectonic plates, as
the plates respond to gigantic pressures from below. The actions of
the tectonic plates had a hand shaping life on earth, and they
continue to affect us today. I very big ways, too. Earthquakes
arise when plates shift, as you know, but the divergent rifts on
some plate boundaries could actually be considered a "functioning
split" because the plates are continuing to move apart, continuing
to split. Remember that the crust of the earth is an evolving
megastructure. The massive dynamics that shaped it in the past
continue to shape it now, even though billions of years of have
passed since the crust formed.
