How was the ocean formed?

Answer 1

God created the ocean.

Some of it would have come from the ice in meteorites.____________________________________When the earth was very young (~4.5 billion years ago), the surface and proto-atmosphere were still very hot, hence no liquid water could form. At some point the proto-atmosphere cooled down enough that liquid water began to condense (from atmospheric water vapor) into clouds, then rain, then accumulations on the surface. This accumulation onto a formerly dry planet became what we now think of as "the ocean."

Now, where did all that water VAPOR come from, you ask? Probably from the interaction of (a) oxygen (or oxide minerals) with (b) hydrogen gas escaping from the solid earth into the proto-atmosphere. But at least a little of the water vapor probably came directly from water ice contained in the space rocks that had long ago congealed into planet earth.