"If there is no way it could ever crystalize when the whole is not at
saturation levels, maybe the oceans have not been receiving salt for very
long."
This is a problem only for your precipitation scenario. In the real world
there are places in the Pacific and the Middle East where ocean water can
become sequestered in lagoons or bays (I'm sure Glenn could explain the
mechanism better) where evaporation would then quickly raise the saturation
level of the remaining water up to, then beyond, that needed for the
various salt species to crystallize out. It's just like what happens when
you dissolve table salt in a glass of water, then let the water evaporate
away. The salt will be left behind as crystals even if the water was not
saturated to begin with.
Kevin L. O'Brien
"Good God, consider yourselves fortunate that you have John Adams to abuse,
for no sane man would tolerate it!" William Daniels, _1776_