What was the evolution of a fluid-filled space separating the digestive tract from the body' s outer layer?

i can't answer your question in very sad situation.

but if your situation is very bad, then you can find happiness by thinking about your past that has full of happiness.

or you should do meditation for some time to get rid off from that bad situation.

the plates spread at mid-ocean ridges (they are divergent plate boundaries) which allows magma to rise through the weakness between the plates. the magma then emerges as lava from the boundary and cools, creating a new crust.